Focus On Science Workbook Grade 8

5. There are three classes of levers based on the locations of the fulcrum, load and effort. Draw a simple model for each class of levers. Then, give two examples of tools for each. (a) First-class lever Effort Fulcrum Load Examples: Pliers, scissors (b) Second-class lever Effort Fulcrum Load Examples: Wheelbarrows, nutcrackers (c) Third-class lever Effort Fulcrum Load Examples: Fishing rods, tweezers 6. Joko is lifting the 30 N box with a force of 5 N using a lever as shown below. 48 ©Praxis Publishing_Focus On Science

(a) What is the mechanical advantage of the lever? Mechanical advantage = Output force Input force = 30 5 = 6 (b) What is the distance between the fulcrum and the box if the distance between the effort and the fulcrum is 3 m? Mechanical advantage = Input distance Output distance 6 = 3 Output distance Output distance = 3 6 = 1 2 m (c) A rock weighing 50 N is placed on top of the box. Find the effort needed to lift them. Mechanical advantage = Output force Input force 6 = 30 + 50 Input force Input force = 80 6 = 13.33 N (d) What is the advantage of using this simple machine? A small effort is needed to lift the large load. (e) Which type of lever always has a mechanical advantage greater than 1? Explain. Second-class lever. Its output distance is always smaller than its input distance. Chapter 3 Work, Energy and Simple Machines 49 ©Praxis Publishing_Focus On Science

7. Akhim built a ramp to move a box from the ground to the elevated floor as shown below. 2 m Box 14 m (a) What type of simple machine is this ramp? Inclined plane (b) How does it help with the work? It reduces the force needed to move the box from a lower level to a higher level. (c) What is the mechanical advantage of the ramp? Mechanical advantage = Input distance Output distance = 14 2 = 7 (d) How much effort is needed to move a 100 N box from the ground to the elevated floor using the ramp? Mechanical advantage = Output force Input force 7 = 100 Input force Input force = 100 7 = 14.3 N (e) What should Akhim do if he wants to further reduce the effort required to move the box? He should use a longer ramp. (f) In reality, will the work done by moving the box without the ramp and using the ramp be the same? Explain. Not the same. The work done with the ramp is greater than the work done without the ramp as extra work is done to overcome the frictional force on the ramp. 50 ©Praxis Publishing_Focus On Science

8. The figure shows an axe that is used to split wood. (a) What type of simple machine is the axe? Wedge (b) Briefly describe this type of simple machine. It consists of one or two inclined planes, giving it a thin end and a thick end. (c) Give another three examples of tools that work based on the same simple machine as the axe. Knives, needles, peelers (d) The figure below shows two axes from their front views. Axe P Axe Q (i) Which axe do you think would require less force to split a piece of wood? Axe Q (ii) Explain your reason. The input distance of axe Q is greater than that of axe P. So, axe Q would do the same amount of work with less input force. 9. (a) Describe a screw as a type of simple machine. A simple machine that has an inclined plane wrapped around a cylinder (b) The figure below shows two types of screws. Screw A Screw B Which of the screws shown above would be easier to drive into a piece of wood? Why? Screw A. The spacing between threads in screw A is smaller, thus its input distance is greater and its input force will be smaller. (c) Why is the mechanical advantage of a screw always greater than 1? The length of the thread of the screw is always greater than the length of the screw. Chapter 3 Work, Energy and Simple Machines 51 ©Praxis Publishing_Focus On Science

10. The figure shows a doorknob. It is an example of a simple machine. Fill in the blanks with the words below to explain how this simple machine works. turned shaft output latch greater easier knob force Shaft Knob A doorknob is an example of a wheel and axle, in which the knob acts as the wheel and the shaft of the doorknob acts as an axle. When the knob is turned, the shaft is turned too, retracting the latch to open the door. A doorknob is a force multiplier. As the knob is larger than the shaft, the knob rotates at a greater distance than the shaft. Therefore, an input force on the knob creates a greater output force on the shaft, making it easier to open the door. 11. The figure shows a system of pulleys. (a) What are pulleys? They are a type of simple machine that consists of a rope and a grooved wheel. (b) What are usually pulleys used for? They are usually used to lift objects. (c) The system of pulleys in the figure is used to lift a block weighing 500 N to a height of 10 m. (i) How much work needs to be done to lift the block? Work = force × distance = 500 × 10 = 5000 J (ii) How far does the cable need to be pulled to lift the block 10 m high if its mechanical advantage is 2? Mechanical advantage = Input distance Output distance 2 = Input distance 10 Input distance = 2 × 10 = 20 m 500 N 52 ©Praxis Publishing_Focus On Science

12. The action of nodding our head uses a lever. (a) What class of lever does this action of nodding the head fall under? First-class lever (b) Label the components of the lever system in the nodding action of the head. Load Effort Fulcrum (c) Fill in the blanks. The point where our skull meets the top of our spine acts as the fulcrum . The weight of the head acts as the load . When the neck muscle at the back of our skull contracts , it acts as the effort to lift our head against the weight of the head. When the neck muscles relax, our head moves downwards . 13.We can lift things in our hands by using our arms as a lever. (a) What type of lever is our arm? Third-class lever (b) Label the parts of the lever in the arm when we lift things. Load Fulcrum Effort Chapter 3 Work, Energy and Simple Machines 53 ©Praxis Publishing_Focus On Science

1. Which of the following is true about work? A Work is a pull or a push upon an object. B Work is done when a force moves an object. C Work is the rate at which a force is applied. D The unit of work is Newtons. 2. In which situation is work said to be done? A A book on a table B A ball rolling at a constant velocity on a frictionless surface C A car making an emergency stop D A house being pushed by a boy 3. The factors affecting the amount of work done on an object include I the mass of the object II the force exerted on the object III the distance moved by the object A I and II only C II and III only B I and III only D I, II and III Question 4 is based on the article below. A simple machine is any device that has very few or almost no moving parts. The term machine is attributed to the Greek playwright Aeschylus (523–426 BC) in reference to theatrical machines such as the “deus ex machina” or “god from a machine.” There are six types of simple machines and when these machines are combined, they can create an even greater mechanical advantage like that of a bicycle. Objective Questions A B C D Choose the best answer. 4. Which is not true about simple machines? A They do not change the amount of work done. B They make our work easier by increasing the output force. C A lorry is an example of a simple machine. D A knife is a simple machine used to cut things. Questions 5 and 6 are based on the figure below. A wooden plank with a length of 2 m is used to lift a box weighing 200 N to a height of 1.5 m. 1.5 m 2 m F 5. What is the work done on the box to move it up the ramp? A 30 J C 300 J B 40 J D 400 J 6. What is the magnitude of F? A 40 N C 100 N B 50 N D 150 N 7. Which is true about renewable energy sources? A These sources can be reused. B Wind and radioactive substances are examples of renewable energy sources. C Renewable energy sources can be used to generate electricity. D They cause water and air pollution. 54 ©Praxis Publishing_Focus On Science

8. A boy weighing 400 N takes 5 s to walk up a flight of stairs as shown below. 5 m 3 m Which of the following statements is/are correct? I The force exerted by the boy is 400 N. II The work done by the boy is 2000 J. III The power output by the boy is 240 W. A I only C I and III only B I and II only D I, II and III 9. Which of the following pairs is matched correctly? Form of energy Situation A Chemical energy Stored in batteries and coal B Kinetic energy In a stretched rubber band C Sound energy In hot things D Potential energy In moving things 10. The information below describes a type of energy source. It is our primary energy source. It gives out heat and light energy. We can convert its energy directly into electrical energy. What energy source is described above? A Sun B Wind C Radioactive energy D Heat inside the Earth 11.A diver is at the top of a 10 m diving platform. She has a mass of 50 kg. What is her potential energy? [1 kg = 10 N] A 5000 J C 1000 J B 2500 J D 500 J 12.Which forms of energy are involved when a car is moving at night? I Electrical energy II Light energy III Chemical energy IV Mechanical energy A I and III only C I, II and III only B II and IV only D I, II, III and IV 13.Which is the correct ratio of the mechanical advantage of a machine? A Output force Input force B Output distance Input distance C Output force Output distance D Output distance Input force 14.Which is not true about a wheelbarrow? A It is a type of lever. B Its load is located between its fulcrum and its effort. C Its effort and load act in the same direction. D A smaller effort is needed to carry a load. 15.What is the mechanical advantage of a machine if a force of 100 N is needed to lift a car weighing 10 000 N? A 100 C 0.1 B 10 D 0.01 16.Which of the following show the correct types of simple machines in our body? I Nodding of the head – First-class lever II Bending of the arm – Second-class lever III Standing on tiptoes – Third-class lever IV Biting an apple with teeth – Wedges A I and II only C II and III only B I and IV only D II, III and IV only Chapter 3 Work, Energy and Simple Machines 55 ©Praxis Publishing_Focus On Science

Complete the concept map below about work, energy and simple machines. Concept Map ability to do work First-class Second-class Third-class Coal Wind Natural gas Sun Petroleum Moving water Nuclear energy Biomass Waves Heat from inside the Earth Gravitational potential energy Elastic potential energy Mechanical energy Power Energy transformation In human body Non-renewable sources Renewable sources Chemical energy Light energy Thermal energy Sound energy Electrical energy Potential energy Kinetic energy Screw Wedge Inclined plane Lever Wheel and axle Pulley Mechanical advantage Work Time Work Simple machines Energy classes types forms source types types types types 56 ©Praxis Publishing_Focus On Science

HOTS Daily Application Amir is trying to lift the lid of a can of paint with a screwdriver as shown below. The screwdriver acts as a simple machine to make the work easier. Explain how this machine works. Would it be easier for him if he uses a long screwdriver instead of a short one? Explain using the mechanical advantage of the simple machine. The screwdriver acts as a lever. The fulcrum is where the screwdriver touches the edge of the can. The load is the lid and the effort is the force applied to the screwdriver. When a force is applied on one end of the screwdriver, the other end goes up and lifts the lid. Mechanical advantage = output force input force = input distance output distance . So, it would be easier to use a long screwdriver. When a long screwdriver is used, the input distance increases. Thus, this increases its mechanical advantage. Therefore, Amir can use a smaller effort to produce a larger output force to lift the lid. Online Quick Quiz Chapter 3 Work, Energy and Simple Machines 57 ©Praxis Publishing_Focus On Science

Vibrations, Waves and Light CHAPTER 4 4.1 Vibrations 1. Tick (✓) the situations that show periodic motion. (a) A hot-air balloon rising in the air (b) A mass moving up and down while suspended on a spring (c) A ball is hit with a racquet (d) A girl swinging on a swing (e) A girl running in a random direction (f) A rotating ceiling fan (g) The Earth orbiting the Sun (h) A horse jumping over the fence ✓ ✓ ✓ ✓ 58 ©Praxis Publishing_Focus On Science

2. What is vibration? A periodic motion in which an object moves back and forth repeatedly about an equilibrium position. 3. Draw the direction of the vibrating object in each situation below once it is released. (a) A load suspended on a spring on a ceiling is pulled downwards (b) A bob of a pendulum is pulled to a side (c) A load attached to a spring on a wall is pulled to a side (d) One end of a ruler is clamped at the edge of a table and the other end is pushed down 4. A boat is idling in the middle of the sea. (a) How does it move? It moves up and down due to the sea waves. (b) Is this motion a periodic motion? Why? It is a periodic motion. The motion repeats itself after a certain period. Chapter 4 Vibrations, Waves and Light 59 ©Praxis Publishing_Focus On Science

5. The figure below shows a loaded spring moving up and down repeatedly. 4 cm 4 cm Spring Load Position P Position R Position Q Position Q Position Q (a) Why is the motion of this loaded spring considered a vibration? The load moves up and down repeatedly about the equilibrium position, Q. (b) Describe a complete cycle of the motion of the loaded spring. Q to R to Q to P to Q (c) (i) What does the amplitude of a vibration mean? The maximum displacement of the object from its equilibrium position (ii) What is the amplitude of the loaded spring? 4 cm (d) (i) What does the period of a vibration mean? What is its unit? The time taken for an object to make a complete cycle. Seconds. (ii) If the loaded spring completes 8 cycles in 12 s, what is its period? 1.5 s (e) (i) What does the frequency of a vibration mean? What is its unit? The number of complete cycles by the vibrating object in a second. Its unit is Hertz. (ii) If the loaded spring completes 8 cycles in 12 s, what is its frequency? 0.667 Hz 6. (a) How is the frequency, f of a vibration related to its period, T? Show its equation. f = 1 T or T = 1 f (b) What is the period of a vibrating object if its frequency is 2 Hz? T = 1 f = 1 2 s 60 ©Praxis Publishing_Focus On Science

4.2 Waves 1. (a) What is a wave? A wave is a disturbance that travels from a vibrating or oscillating source. (b) What do waves carry? Energy (c) Do waves transfer matter as they travel? No (d) State three examples of waves. Water waves, electromagnetic waves and sound waves (e) There are two types of waves based on the direction of movement of particles in the medium relative to the direction of the waves. Name them. Transverse and longitudinal waves 2. Fill in the blanks to describe two types of waves. longitudinal light sound transverse perpendicular parallel water Wave direction Direction of vibrations (a) A transverse wave is a wave that has vibrations in the direction perpendicular to the direction the wave travels. Examples of this type of wave are water waves and light waves. Direction Wave direction of vibrations (b) A longitudinal wave is a wave that has vibrations in the direction parallel to the direction the wave travels. An example of this type of wave is sound waves. Extra Info Longitudinal and transverse waves i Chapter 4 Vibrations, Waves and Light 61 ©Praxis Publishing_Focus On Science

3. Match the descriptions of waves to the correct terms. (b) The part of a transverse wave in which it rises to the highest point Rarefaction (c) The part of a transverse wave in which it sinks to the lowest point Trough (d) The part of a longitudinal wave in which the particles are further apart Crest (a) The part of a longitudinal wave in which the particles are closer Compression 4. (a) What does the wavelength of a wave mean? The distance covered by a full cycle of the wave (b) Mark the wavelength, λ for each of the following waves. Describe it. (i) A longitudinal wave λ λ λ λ λ The distance between two consecutive rarefactions or compressions (ii) A transverse wave λ λ λ λ λ λ The distance between two consecutive troughs or crests Extra Info Wavelengths i 62 ©Praxis Publishing_Focus On Science

5. The figure below shows a wave. Its frequency is 0.2 Hz. 80 cm 16 cm (a) How many complete waves are shown? 4 (b) What is the amplitude of the wave? 8 cm (c) What is its wavelength? 20 cm (d) What is its period? T = 1 f = 1 0.2 = 5 s (e) What is the speed of the wave? v = λ T = 20 5 = 4 cm s–1 6. We can categorise waves into mechanical waves and electromagnetic waves. (a) What is the difference between these two types of waves? Mechanical waves: Need a medium to travel Electromagnetic waves: Do not need a medium to travel (b) Give two examples for each type of wave. Mechanical waves: Sound waves, water waves Electromagnetic waves: Radio waves, X-rays (any other correct answers) (c) State two other properties of electromagnetic waves. Electromagnetic waves travel at the speed of light in a vacuum (3 × 108 m s−1 ). Electromagnetic waves contain an electric field and a magnetic field. Chapter 4 Vibrations, Waves and Light 63 ©Praxis Publishing_Focus On Science

7. How is the sound produced in each of the following situations? (a) A buzzing sound from a honey bee From the vibrations of the wings when the bee flies (b) A guitar is strummed From the vibrations of the strings of the guitar when they are strummed (c) A drum is hit From the vibrations of the drum skin when it is hit (d) A pair of maracas is shaken From the vibrations of the beans in the maracas when they hit against the wall and between themselves 8. Fill in the blanks with the given words. gases fast longer closely different far solids liquids mediums Sound travels at different speeds through different mediums . Sound travels more quickly through solids than through liquids and gases. The molecules of a solid are closely packed together and this allows the vibrations to be passed from one molecule to the next very fast . In a gas, the molecules are very far apart. Thus, it takes a longer time for the vibrations to be passed from one molecule to the next one in gases. Therefore, sound travels the fastest in solids and the slowest in gases . 64 ©Praxis Publishing_Focus On Science

9. Tom and Jim are playing with a set of paper cup telephone. When Jim whispers into his cup, Tom can hear clearly through his cup even though they are far apart. Tom Jim (a) Explain briefly how Tom can hear clearly. The vibration of Jim’s voice travels to his cup and then along the string to Tom’s cup. As the sound travels through solid mediums (the cups and the string), it travels more effectively than through gas (air). (b) In what ways can they improve the effectiveness of the paper cup telephone? List two ways. Keep the string taut. Prevent the string from coming into contact with any other objects. (c) Can they play with this set of telephone cups if they were living on the Moon? Explain your answer. No. There is no air on the Moon for the vibrations to reach the cups and their ears. 10. Fill in the blanks to show how sound travels from a drum to our ears. sound repeatedly outwards spread eardrums compressed compression rarefaction vibrates When we beat a drum, the tight skin of the drum vibrates very fast up and down. As the drum skin moves up, the air molecules above it are pushed and compressed , forming a region of high pressure known as compression . When the drum skin moves down, the air molecules are spread out, forming a region of low pressure known as rarefaction . Extra Info How sound travels i Chapter 4 Vibrations, Waves and Light 65 ©Praxis Publishing_Focus On Science

The air molecules above the drum skin are compressed and spread out repeatedly as the drum skin vibrates. This causes the neighbouring air molecules to be compressed and spread out too, making the vibrations move outwards . This series of rarefactions and compressions of air molecules are detected by our eardrums . Our eardrums vibrate accordingly and our brain interprets them as sound . 11. Number the steps to show the sequence of how we hear sound. The tiny hairs respond to the movement of the fluid by producing tiny electrical signals. 5 The vibrations of a sound travels through the ear canal and hit the eardrum. 1 The vibrations reach the cochlea which is filled with fluid and tiny hairs. 4 The eardrum vibrates. 2 The sound vibrations make their way through the ossicles, which amplify them. 3 The electrical signals travel along the auditory nerve to the brain where they are then translated into recognisable and meaningful sounds. 6 12. (a) What does the pitch of a sound mean? How high or low a sound is (b) How does the pitch of a sound relate to the frequency of the sound? A sound with a higher frequency has a higher pitch. (c) How does the loudness of a sound relate to the amplitude of the sound waves? A loud sound has a greater amplitude. (d) The figures below show four sound waves. Describe the amplitude and frequency of each wave. (i) Time Amplitude High amplitude, high frequency (ii) Time Amplitude Low amplitude, low frequency 66 ©Praxis Publishing_Focus On Science

(iii) Time Amplitude Low amplitude, high frequency (iv) Time Amplitude High amplitude, low frequency 13. Dian has six similar empty bottles. She fills them with different amounts of water as shown below. (a) When she blows across the tops of the bottles, she realises that they produce different sounds. (i) Why do the bottles produce sound when they are blown across their tops? The air in the bottles vibrates, producing sound waves that we can hear. (ii) Which bottle produces a sound with the highest pitch when it is blown? Why? The bottle with the most water. The column of air is shorter and the air vibrates faster, producing a high-pitched sound. (b) Instead of blowing across the tops of the bottles, now Dian taps the bottles with a spoon. (i) Why do the bottles produce sound when they are tapped? When the bottles are tapped, the water molecules vibrate, creating sound waves that we hear. (ii) Which bottle produces a sound with the highest pitch when it is tapped? Why? The bottle with the least water. When there is less water in the bottle, the water molecules vibrate faster which produces a high-pitched sound. Chapter 4 Vibrations, Waves and Light 67 ©Praxis Publishing_Focus On Science

(iii) One of the bottles is tapped softly and then harder. Describe the difference in the sounds produced. When it is tapped softly, a softer sound is produced. When it is tapped harder, a louder sound is produced. 14. You are given a model of a guitar made from a shoe box and some rubber bands as shown below. State two modifications you can make to the model to produce sounds with a different pitch when the rubber bands are plucked. Use rubber bands with different thickness. Stretch the rubber band across the shorter width of the box. 15.An experiment was carried out to investigate the changes in the frequency of sound produced by a moving source detected by a stationary observer. The sound source produces a sound with a constant frequency. Experiment I II Velocity of the sound source (m s–1) 0 10 Frequency of the sound detected by the stationary observer (Hz) 900 874 (a) What were the responding and manipulated variables in that experiment. Responding variable: Frequency of the sound detected by the stationary observer Manipulated variable: Velocity of the sound source (b) Was the sound source moving towards or away from the observer in Experiment II? Explain. Moving away from the observer. The frequency of the detected sound was decreasing. (c) Name this phenomenon. Doppler effect 68 ©Praxis Publishing_Focus On Science

(d) How does the pitch of a sound heard by an observer differ when the sound source is approaching and moving away from the observer? Approaching the observer: The pitch is higher. Moving away from the observer: The pitch is lower. 16. The underlined words are incorrect. Replace them with the correct words. (a) Like light, sound can refract when it hits a hard surface. reflect (b) An echolocation is the reflection of a sound wave from a surface back to the listener. echo (c) An auditorium usually has large curtains and carpeted floors to enhance the production of echoes. reduce (d) Echo is the technique used by some animals to determine the locations of distant objects using the reflection of sound. Echolocation (e) We can hear sounds with frequencies between 200 Hz and 20 000 Hz. 20 (f) Ultrasound is sounds with frequencies below 20 Hz. Infrasound (g) Infrasound is sounds with frequencies above 20 000 Hz. Ultrasound (h) The loudness of a sound is measured with a sound meter in lux. decibels (i) Long exposure to loud sound can cause permanent damage to the brain. ears 4.3 Light and Optical Instruments 1. Tick (✓) the correct statements about light. (a) Light travels in straight lines. ✓ (b) The speed of light is about 3 × 108 m s–1. ✓ (c) Light is a form of energy. ✓ (d) Non-luminous objects give out light. (e) White light is made up of seven colours. ✓ (f) The sequence of the colours in a rainbow is orange, red, yellow, green, blue, indigo and violet. (g) Transparent objects allow light to pass through them. ✓ (h) Shadows are cast when light cannot pass through opaque objects. ✓ Chapter 4 Vibrations, Waves and Light 69 ©Praxis Publishing_Focus On Science

2. What is the bouncing of light off a surface known as? Reflection of light 3. The figure below shows a light ray hitting a mirror. Angle of incidence Angle of Incident ray reflection Reflected ray Mirror Normal (a) Draw the light ray after it hits the mirror in the figure above. (b) Name all the light rays in the figure above. (c) (i) What does normal mean in the reflection of light? The imaginary line drawn perpendicular to the surface of the mirror (ii) Indicate the normal in the figure above. (d) (i) What does the angle of incidence mean? The angle between the incident ray and the normal (ii) Indicate the angle of incidence in the figure above. (e) (i) What does the angle of reflection mean? The angle between the reflected ray and the normal (ii) Indicate the angle of reflection in the figure above. (f) What does the law of reflection state? The incident ray, normal and reflected ray lie in the same plane. The angle of incidence and the angle of reflection are the same. 4. A light ray is incident on a mirror, making an angle of 20° with that surface as shown below. Mirror 20° (a) What is the angle of incidence? Angle of incidence = 90° – 20° = 70° Extra Info Law of reflection i 70 ©Praxis Publishing_Focus On Science

(b) What is the angle of reflection? Angle of reflection = angle of incidence = 70° 5. State the characteristics of an image formed by a plane mirror. The image is virtual, upright, laterally inverted and of the same size as the object. The distance of the image from the mirror is the same as the distance of the object from the mirror. 6. The figure below shows an object in front of a plane mirror. Draw the ray diagram to show how the image is formed when seen by the observer. Observer Plane mirror 7. What is the refraction of light? Refraction of light is the bending of light at the boundary when it travels through different mediums with different densities. 8. Draw how the three light rays refract when entering and leaving the glass block below. Glass block Chapter 4 Vibrations, Waves and Light 71 ©Praxis Publishing_Focus On Science

9. (a) What happens when a light ray travels from a dense medium to a less dense medium? It will refract away from the normal. (b) What happens when a light ray travels from a less dense medium to a denser medium? It will refract towards the normal. 10. Fill in the blanks based on the figures below. bent away higher refracted Air Water Image (a) The pencil submerged partially in the water appears to be bent . This is because the light rays coming from the pencil are refracted at the water-air boundary and bend away from the normal before entering our eyes. The pencil appears to be higher and farther than it is. refracted temperatures dense mirage refraction Light ray from sky Cool air Mirage Hot air (b) On a hot day, we sometimes see a puddle of water in front of us and when we approach it, it disappears. This phenomenon is known as a mirage . It is caused by light refraction . This happens when the light rays pass through the layers of air with different temperatures . The hotter layer nearer the ground is less dense compared to the cooler layers in the upper region. As the light rays from the sky travel through the layers of air, they are refracted before entering our eyes. We see the image of the sky on the ground. Extra Info Mirage i 72 ©Praxis Publishing_Focus On Science

11. There are two types of lenses. Describe their physical properties. (a) Convex lenses: The centre is thicker than the edges. (b) Concave lenses: The edges are thicker than the centre. 12. Complete the ray diagrams below to show how the images are formed by a convex lens. State the characteristics of the images formed. (a) (b) 2F F O F 2F 2F F O F 2F The image is virtual, upright and magnified. The image is real, inverted and magnified. (c) (d) 2F F O F 2F 2F F O F 2F The image is real, inverted and the same size. The image is real, inverted and diminished. 13. Complete the ray diagram below to show how the image is formed by a concave lens. State the characteristics of the image formed. The image is virtual, upright and diminished. Object F Image F Chapter 4 Vibrations, Waves and Light 73 ©Praxis Publishing_Focus On Science

14. The figure below shows the cross-section of a human eye. Label the parts of the eye. Lens Retina Iris Pupil Ciliary body Optic nerve Cornea 15. Number the steps to show the correct sequence of the mechanism of vision in humans. The photoreceptors on the retina turn the light into electrical signals. 5 The light enters our eye through the cornea. 1 Then, the light passes through the lens behind the pupil and is refracted. 3 It then passes through the pupil, an opening at the centre of the iris. 2 The light rays are focused on the retina to form a real, inverted and diminished image. 4 The electrical signals travel from the retina through the optic nerve to the brain for interpretation. 6 16.Write TRUE for each correct statement. Write FALSE for each incorrect statement. (a) The cornea is the curved transparent layer in front of the eye. TRUE (b) The lens focuses the light to form a sharp image on the retina. TRUE (c) The iris controls the size of the pupil, thus controlling the quality of light entering the eye. (d) The lens thickens to focus light from distant objects. FALSE (e) The retina has three types of photoreceptors to produce nerve impulses. FALSE FALSE 74 ©Praxis Publishing_Focus On Science

(f) The pupil becomes smaller in dark places. FALSE (g) The images that fall on the blind spot will not be detected. TRUE (h) The cone cells on the retina are responsible for the detection of colours. TRUE 17. Fill in the blanks to describe how a magnifying glass works. F O F Object Image focal point same virtual magnified convex The magnifying glass consists of a single convex lens. The object needs to be placed between the focal point of the lens and the lens. The image is formed on the same side of the object. The image is virtual , upright and magnified . 18. The figures below show how light rays from distant objects are focused on the retinas of two students. Student M Student N (a) Can student M see distant objects clearly? Why? Yes. Sharp images are formed on the retina. (b) Can student N see distant objects clearly? Why? No. Blurred images are formed on the retina. (c) (i) Name the visual defect student N has. Short-sightedness (ii) Suggest one cause for this defect. The eye lenses are too thick. (iii) State the type of lenses in spectacles that can be used to correct this defect. Concave lens Extra Info Short sightedness i Chapter 4 Vibrations, Waves and Light 75 ©Praxis Publishing_Focus On Science

1. Which is not correct about vibration? A A vibrating object moves back and forth repeatedly about its equilibrium position. B Periodic motion is a type of vibration. C An example of vibration is a swinging pendulum bob. D Two properties of a vibration are its frequency and amplitude. 2. One end of a plastic ruler is pressed on the edge of a table. The other end is pushed down and released. It vibrates as shown below. Q P R Which shows a complete cycle of the motion of the vibrating end of the ruler? A P-Q-R C Q-P-Q-R-Q B P-Q-R-Q D R-Q-P-Q-P 3. A swinging pendulum bob makes 25 complete cycles in 10 seconds. Which shows its correct period and frequency? Period (s) Frequency (Hz) A 2.5 0.4 B 0.4 2.5 C 250 2.5 D 0.4 250 4. Which of the following is not correct about waves? A A wave is a travelling disturbance from a vibrating source. Objective Questions A B C D Choose the best answer. B Transverse and longitudinal waves are two types of waves. C Light and sound are examples of waves. D Air molecules can travel with the waves to other places. Read the text below and answer questions 5 and 6 based on it. Rudy lives by the sea. He notices that the waves never fail to splash on the beach. So far, he has never seen the beach completely submerged nor the sea being emptied. 5. What creates constant sea waves? A The Sun B Aquatic animals C Earthquakes D Wind 6. Which of the following best explains Rudy’s observation? A Sea waves carry only energy to the shore, not water molecules. B The sea water on the beach seeps back to the sea through the sand. C Sea waves break once they hit the beach. D Waves are a type of disturbance in the sea. 7. A type of wave is transporting energy from right to left. The particles of the medium are moving back and forth in a leftward and rightward direction. This type of wave is known as A a mechanical wave B an electromagnetic wave C a transverse wave D a longitudinal wave 76 ©Praxis Publishing_Focus On Science

8. The figure below shows a displacementtime graph of a wave. Displacement (m) Time (s) T V U S Which represent the period and the amplitude? Period Amplitude A V S B U T C S V D T U 9. The displacement-distance graph below shows the motion of a wave. The source of the wave gives out 20 complete cycles in one second. Displacement (cm) 6 25 0 -6 Distance (cm) Calculate the speed of the wave. A 500 cm s–1 C 250 cm s–1 B 400 cm s–1 D 100 cm s–1 10.When someone knocks on your door, you can hear it because sound travels through to reach you. I solid III gas II liquid A I only C II and III only B I and III only D I, II and III 11. The frequency of a sound gives the sound its A loudness C tone B pitch D quality 12.Which shows the function of the human ear part correctly in the hearing process? A The pinna vibrates when the sound waves hit on it. B The ossicles amplify the vibrations. C The cochlea helps to direct the sound waves into the inner ear. D The auditory nerve changes the vibrations into electrical signals. Read the text below and answer questions 13 and 14 based on it. Contrary to popular belief, bats are not blind. They just do not see as well as they hear. By emitting a high frequency pulse of sound and listening to where the sound bounces back, they can identify objects and navigate in the dark. 13.What is the technique used by bats as described? A Sonar B Sound navigation C Echolocation D Doppler effect 14.What are other animals that use the same technique to hunt or navigate? I Dolphins II Whales III Bears A I only C II and III only B I and II only D I, II and III 15. The figure below shows a light ray reflected from a plane mirror at 30°. 30° What is the angle of incidence? A 30° C 60° B 45° D 90° Chapter 4 Vibrations, Waves and Light 77 ©Praxis Publishing_Focus On Science

16. The figure below shows a boy standing 2 m in front of a plane mirror. Then, the mirror is moved 1 m further away from the boy. Plane mirror Boy 2 m What is the distance between the boy and his new image now? A 2 m C 4 m B 3 m D 6 m 17.Which statement is true about a light ray travelling through a glass block from the air? A The incidence angle is the same as the reflected angle. B The light ray travels slower in the glass block. C The light ray bends away from the normal. D The light ray disperses into seven colours in the glass block. 18. If we observe a pebble in a pond, the pebble would appear to be A deeper in the water than it really is B of same depth in the water as it is C nearer to the surface than it really is D invisible 19.K to O are parts of the human eye. J – Brain K – Pupil L – Lens M – Cornea N – Optic nerve O – Retina Which is the correct pathway of light in the human eye? A M, L, K, N, O, J B M, K, L, O, N, J C M, K, L N, O, J D M, L, N, O K, J 20.Which of the following shows the correct ray diagram for the image formed by a convex lens where F is the focal point? A 2 F F F F Image Object B 2 F F F Image Object C 2 F F F Image Object D F F Object Image 21. The information above describes the vision defect suffered by Yatim. Yatim cannot see distant objects clearly but he can see near objects clearly. Which of the following statements is correct about the vision defect? A This vision defect is known as longsightedness. B Yatim’s eye ball is too short. C The images of the distant objects are focused behind his retina. D This defect can be overcome by wearing spectacles with concave lenses. 22.Which optical instrument involves the reflection of light? A Driving mirror B Magnifying glass C Microscope D Telescope 78 ©Praxis Publishing_Focus On Science

Complete the concept map below Concept Map about vibrations, waves and light. Longitudinal waves Sound waves Water waves Doppler effect Reflection Refraction Optical lenses Convex lenses Concave lenses • Apparent depth • Mirage • Rainbows • Pinhole camera • Cameras • Magnifying glass • Spectacles • Telescopes Echo • Pitch • Loudness • Intensity Eardrum ↓ Ossicles ↓ Cochlea ↓ Auditory nerve ↓ Brain Cornea ↓ Pupil ↓ Lens ↓ Retina ↓ Optical nerve ↓ Brain Transverse waves • Complete cycle • Displacement • Amplitude • Period, T • Frequency, f Mechanical waves (require a medium) Electromagnetic waves (do not require a medium) v = λ T Vibrations Waves = fλ Light related terms types pathway of hearing mechanism pathway of vision mechanism Category of waves example formula for speed example optical instruments example properties effects types properties Chapter 4 Vibrations, Waves and Light 79 ©Praxis Publishing_Focus On Science

HOTS Daily Application Kassim and Dian were hiking through a canyon. While standing on the edge a mountain, they were wondering how far the nearby canyon wall was. Kassim let out a scream. An echo was heard 1.2 s after the scream. If the speed of sound waves in the air is 342 m s–1, help them find the distance between them and the nearby canyon wall. Speed of sound, v = 342 m s–1, Time taken for sound to travel two-way distance (to and back) = 1.2 s So, time taken for sound to travel one-way distance, t = 0.6 s Distance, d = vt d = 342 × 0.6 = 205.2 m The distance between them and the nearby canyon wall is 205.2 m. Online Quick Quiz 80 ©Praxis Publishing_Focus On Science

Assessment 1 Section A [40 marks] Choose the best answer. Answer all questions. 1. Which of the following parts of a light microscope is matched correctly to its function? Part Function A Lens Magnifies the image of the specimen B Condenser Controls the amount of light into the diaphragm C Mirror Intensifies the light onto the specimen D Knob Holds and supports the lens 2. The figure shows a plant cell. P What will happen to P if the plant does not receive water for a few days? A It will fill up with air instead of water and expand. B It will shrink. C It will disintegrate and appear again when there is water. D It will remain the same. 3. Which is a unicellular organism? A Mucor C Hydra B Spirogyra D Euglena 4. Budi loves to eat fried chicken and fries. W What would happen if he takes his favourite food for every meal? A He might have difficulties defaecating. B He might lose weight very fast. C He might suffer from kwashiorkor and marasmus. D He might feel weak and tired. 5. Why does a pregnant lady need to eat more? A To support the extra mass she is gaining B For the growing foetus C For her rapid growth D To prevent herself from contracting any diseases 6. Which is not a purpose of using food additives? A To prohibit the growth of harmful microorganisms B To add nutrients to the food C To ensure there is enough food for everyone D To make the food looks more appealing 7. Proteins are broken down into peptides and polypeptides. Where does the digestion mentioned above first occur in our digestive system? A Mouth B Stomach C Small intestine D Large intestine Assessment 1 81 ©Praxis Publishing_Focus On Science

8. The information below describes a component of the human circulatory system. • Circulating fluid • Carries useful and waste materials What is that component? A Blood B Heart C Red blood cells D Blood vessels 9. Which of the following is correct about the human heart? A The left part of the heart is thicker than the right part. B The aorta carries deoxygenated blood from the heart to the lungs. C The valves in the heart prevent the mixing of oxygenated and deoxygenated blood. D The vena cava carries oxygenated blood from the lungs into the heart. 10.Which is not part of the human respiratory system? A Trachea C Heart B Alveolus D Bronchus 11. How are the alveoli in the lungs able to function effectively? I Alveoli are surrounded by blood capillaries. II Alveoli have walls that are one-cell thick. III The shape of alveoli provides a large surface for gas exchange. IV Alveoli have walls that are semipermeable to gases. A I, II and III only B I, II and IV only C I, III and IV only D II, III and IV only Questions 12 and 13 are based on the diagram below. 3 m 6 m 4 m 12. Joko carried a box weighing 300 N up a flight of stairs of 4 m high and 3 m wide. Then, he pushed the box on the floor with a force of 150 N for 6 m. How much work was done in total? A 1 800 J B 2 100 J C 2 500 J D 3 000 J 13. Calculate the power of Joko if he took 10 seconds to complete it. A 180 W B 210 W C 250 W D 300 W 14.A bob of a pendulum is swinging from P to Q to R and back to Q and lastly to P. P R Q At which point does the bob have the highest kinetic energy and potential energy? Highest kinetic energy Highest potential energy A P Q B P R C Q R D R P 82 ©Praxis Publishing_Focus On Science

15. The two simple machines shown below are from the same class of lever. Which statement is not true about their class of lever? A The load is positioned between the fulcrum and the effort. B Their mechanical advantage is always greater than one. C A bottle opener is another example of this class of lever. D The input force is always greater than its output force. 16. The figure below shows a displacementtime graph of a wave. Displacement (cm) 1 Time (s) 0 2 2 4 6 -6 -4 -2 3 Which is true about the wave? I The amplitude of the wave is 6 cm. II There are 2 cycles of the wave shown. III Its wavelength is 2 s. A I only C I and III only B I and II only D I, II and III 17. The figure shows a structure of a human ear. Which is the correct function of R? A Vibrates when sound waves hit it B Detects vibrations and converts them into nerve impulses C Carries nerve impulses to the brain D Equalises the air pressure on both sides of the eardrums 18. Which is true about sounds? A Humans can hear sounds with a frequency between about 20 Hz and 20 000 Hz. B Infrasound describes sounds with a frequency above 20 000 Hz. C Exposure to sounds with low decibels for a long period of time can damage our eardrums. D Some animals use the Doppler effect to determine the location of their prey. 19.An image of a pencil is observed on a plane mirror. The distance between the mirror and the image is 15 cm. Mirror Object Image 15 cm If the pencil is moved 3 cm towards the mirror, what would be the distance between the image and the object? A 36 cm C 27 cm B 30 cm D 24 cm 20.Which of the following use lenses to function? I Magnifying glasses II Periscopes III Kaleidoscopes IV Microscopes A I and II only C II and III only B I and IV only D III and IV only Assessment 1 83 ©Praxis Publishing_Focus On Science

Section B [60 marks] Answer all questions. 1. The figure below shows a plant cell. P: Cell wall S: Nucleus Q: Cell membrane T: Vacuole R: Chloroplast U: Mitochondrion (a) Name the parts labelled P, Q, R, S, T and U in the figure above. [6 marks] (b) Using the letters in the figure, name three structures that are not found in a typical animal cell. P, R and T [3 marks] 2. (a) What are specialised cells? They have different shapes and structures to carry out different functions. [1 mark] (b) State the main function of each specialised cell of plants stated below. Palisade cells: Contain a lot of chloroplasts to carry out photosynthesis Phloem: Transports food from the leaves to other parts of the plants Xylem: Transports water from the roots to the leaves [3 marks] (c) State the main function of each specialised cell of animals stated below. Muscle cell: Contracts and relaxes to produce movements Nerve cell: Carries information in the form of nerve impulse to different parts of the body Red blood cell: Transports oxygen to all parts of the body [3 marks] 3. Carbohydrates, proteins and vitamins are three types of nutrients that our body needs. (a) State one function of each type of nutrient. Carbohydrates: To provide energy for the body 84 ©Praxis Publishing_Focus On Science

Proteins: To build and repair body cells and tissues Vitamins: To maintain good health and growth [3 marks] (b) Besides the three types of nutrients mentioned above, name three other types of nutrients needed by our body. Fat, water and minerals [3 marks] 4. The figure shows the apparatus set-up of an experiment. Distilled water maintained at 37°C Visking tube Boiling tube A B Starch solution Glucose solution The water outside the Visking tube of test tubes A and B was tested for the presence of starch and glucose for 8 minutes. The results are shown below. Time (min) Test tube A Test tube B Test for starch Test for glucose Test for starch Test for glucose 0 Absent Absent Absent Absent 2 Absent Absent Absent Trace 4 Absent Absent Absent Trace 6 Absent Absent Absent Abundant 8 Absent Absent Absent Abundant (a) Make an inference based on the results. Starch molecules are big and cannot pass through the Visking tube into the surrounding water. Glucose molecules are small and can pass through the Visking tube. [1 mark] (b) Make a conclusion based on the results in the table. Glucose molecules are smaller than starch molecules. [1 mark] (c) (i) Predict how the results in test tube A will be different if some human saliva is added to the starch solution. The results will be the same as the results of test tube B. [1 mark] Assessment 1 85 ©Praxis Publishing_Focus On Science

(ii) Explain your prediction. The amylase in the human saliva will convert the starch in the Visking tube into glucose. The glucose molecules will move out from the Visking tube into the water in the test tube. [2 marks] 5. The figures below show the human thorax during breathing. Diaphragm Diaphragm X Y (a) What does inhalation mean? Taking in the air from the atmosphere into the lungs [1 mark] (b) (i) Which figure shows inhalation? X [1 mark] (ii) Explain your answer. The diaphragm flattens out during inhalation. [1 mark] (c) During exhalation, the volume of the thoracic cavity decreases. List two factors that contribute to the decrease in the volume of the thoracic cavity. The diaphragm relaxes and arches upwards. The rib cage moves downwards and inwards. [2 marks] (d) Our atmosphere is made up of oxygen (21%), carbon dioxide (0.04%) and nitrogen (78%). List the percentages of oxygen, carbon dioxide and nitrogen in the air we exhale. Oxygen: 16% Carbon dioxide: 4% Nitrogen: 78% [3 marks] 86 ©Praxis Publishing_Focus On Science

6. T and U are two groups of energy sources. Group T: Wind energy, solar energy, wave energy and geothermal energy Group U: Fossil energy and nuclear energy (a) Identify the groups of energy sources, T and U. T: Renewable sources of energy U: Non-renewable sources of energy [2 marks] (b) State an advantage of using the energy sources in group T over the energy sources in group U. The energy sources in group T can replenish themselves and will not be depleted. // The energy sources in group U have a limited supply and will eventually run out. [1 mark] (c) Name two other energy sources that can be grouped under group T. Hydroelectric energy and biomass energy [2 marks] (d) (i) Name three major forms of fossil energy. Coal, petroleum, natural gas [3 marks] (ii) State another disadvantage of using fossil energy besides the one mentioned in (b). They pollute the environment as they emit carbon dioxide when they are burnt. [1 mark] 7. The figures show two graphs pertaining to a wave. Height (cm) 0 Time (s) 5 10 -15 15 0 Distance (cm) 10 20 30 40 50 -15 15 Height (cm) (a) State the amplitude of the wave. 15 cm [1 mark] (b) What is the wavelength of the wave? 40 cm [1 mark] (c) What is the period of the wave? 10 seconds [1 mark] Assessment 1 87 ©Praxis Publishing_Focus On Science

(d) Find the frequency of the wave. Frequency, f = 1 Period = 1 10 = 0.1 Hz [1 mark] (e) Find the velocity of the wave. Velocity = fλ = 0.1 × 40 = 4 cm s–1 [1 mark] 8. (a) State the functions of the following parts of a human eye. Lens: To focus light on the retina to form a sharp image Iris: To control the amount of light entering the eye Retina: To detect light and produce nerve impulses Optic nerve: To carry nerve impulses to the brain to be interpreted [4 marks] (b) Draw the rays on the figure below to illustrate how an image of the object is formed in the human eye. [4 marks] (c) Yanti has a vision problem. Her doctor diagnosed her problem as short-sightedness. (i) Describe Yanti’s vision condition. She sees near objects clearly but far objects appear blurry. [1 mark] (ii) State one cause of Yanti’s vision problem. Her eye lenses are too thick./Her eyeballs are too long. [1 mark] (iii) How can the doctor fix Yanti’s vision problem? Yanti has to wear a pair of spectacles with concave lenses. [1 mark] 88 ©Praxis Publishing_Focus On Science

Elements, Compounds and Mixtures CHAPTER 5 5.1 Atoms and Molecules 1. (a) What is matter? Matter is anything that takes up space and has mass. (b) What is an atom? An atom is the basic building unit for all matter. (c) Can we see atoms? Explain your answer. No, because atoms are very tiny. They can only be seen with an electron microscope. 2. (a) What are subatomic particles? Subatomic particles are tiny particles in an atom. (b) Name the subatomic particles found in an atom. Protons, electrons and neutrons (c) Draw a simple atom in the space provided below. Label its subatomic particles. Electron Neutron + + + - - - Proton (d) Fill in the table to show the properties of the subatomic particles. Subatomic particle Charge Location Relative mass (amu) Proton +1 In the nucleus 1 Electron –1 Outside the nucleus 1 1 840 Neutron 0 In the nucleus 1 Extra Info Subatomic particles i Chapter 5 Elements, Compounds and Mixtures 89 ©Praxis Publishing_Focus On Science

3. (a) An atom has no charges. How is this possible when it contains electrons and protons? In an atom, the number of protons which are positively charged and the number of electrons which are negatively charged are equal. Therefore, the charges cancel each other leaving the atom without any charges. (b) Why is the nucleus of an atom always positively charged? The nucleus is made up of the positively-charged protons and the neutral neutrons. Thus, the nucleus is always positively charged. 4. Tick (✓) the correct statements. (a) The nucleus of an atom is made up of neutrons only. (b) The electrons are found orbiting the nucleus. ✓ (c) The mass of an atom is mostly concentrated at its nucleus. ✓ (d) An atom always has more protons than electrons. (e) All the subatomic particles of an atom have charges. 5. (a) What is a molecule? A molecule is made up of two or more atoms that are held together by chemical bonds. (b) Fill in the chart to classify the types of molecules and give two examples each. examples Nitrogen gas, oxygen gas Molecules of an element types Water, carbon dioxide examples Molecules of a compound Molecules (c) State one difference between these two types of molecules. A molecule of an element is made of two or more atoms of the same type. A molecule of a compound is made up of two more different types of atoms. 90 ©Praxis Publishing_Focus On Science

5.2 Elements 1. What is an element? An element is a pure substance that cannot be broken down further into simpler substances. 2. (a) What is iron made up of? Iron atoms (b) What is oxygen made up of? Oxygen atoms (c) Draw the atoms in iron and oxygen. (i) (ii) Iron Oxygen (d) Are iron and oxygen elements? Explain. Yes. Both are made up of one type of atom. 3. (a) What is an element symbol? It is a one- or two-letter abbreviation that is used to represent a chemical element. (b) State the symbols for these elements. Element Symbol Element Symbol Element Symbol Hydrogen H Zinc Zn Nitrogen N Sodium Na Magnesium Mg Calcium Ca (c) O is the symbol for oxygen. Is O2 similar to 2O? Explain with suitable diagrams. O O O2 O2 is a molecule of the element oxygen. It has two oxygen atoms bonded chemically together. O O 2O 2O has two free (not bonded) oxygen atoms. Chapter 5 Elements, Compounds and Mixtures 91 ©Praxis Publishing_Focus On Science

4. The figure below shows a part of the Periodic Table of Elements. (a) State two functions of the Periodic Table. To make the study of elements easier and to predict the properties of the elements (b) (i) What are the horizontal columns known as? Periods (ii) How many horizontal columns are there? 7 periods (c) (i) What are the vertical columns known as? Groups (ii) How many vertical columns are there? 18 groups 5. The underlined words are incorrect about the Periodic Table of Elements. Replace them with the correct words. (a) Each vertical column of elements in the Periodic Table is known as a period. group (b) There are 18 periods of elements. 7 (c) The elements in Group 1 are also known as acidic metals. alkali (d) The elements in Group 3 are also known as alkaline earth metals. 2 (e) Halogens are found in Group 5. 17 (f) The property of elements in the table changes from being metallic to non-metallic from middle to right. left (g) Metals are found in Groups 13 to 16. Metalloids 92 ©Praxis Publishing_Focus On Science

6. The figure below shows a part of the Periodic Table of Elements. Shade it to identify the position of metals, nonmetals, metalloids and noble gases. H Ge Noble gases Metalloids Non-metals Metals Key: 7. Group these elements into metals, non-metals and metalloids. Zinc Hydrogen Carbon Boron Silicon Barium Polonium Germanium Calcium Neon Aluminium Oxygen Metals Zinc Calcium Aluminium Barium Non-metals Neon Oxygen Carbon Hydrogen Metalloids Boron Germanium Polonium Silicon 8. Zaki has a copper rod. (a) He polishes it with sandpaper. What does he observe? The rod becomes shiny. (b) Can he melt it with the Bunsen burner? Explain your reason. No. Copper is a metal. It has a very high melting point. (c) (i) Zaki hammers the rod with a hammer. What will happen to it? It will change its shape without breaking. (ii) What term is used for the physical property displayed by the rod in activity (c)(i)? Malleable (d) Is copper a good conductor of electricity? Give an example of how it is used. Yes. It is used in electric cables to conduct electricity. Extra Info Metals, non-metals and metalloids i Chapter 5 Elements, Compounds and Mixtures 93 ©Praxis Publishing_Focus On Science

9. A simple experiment is shown below. Rods X and Y are made of different materials. A thumbtack was attached with wax to the end of each rod. The other ends of the rods were heated. X Wax Thumbtack Wax Thumbtack Y The thumbtack attached to rod X fell first and then followed by the thumbtack attached to rod Y. Which rod is more likely made of non-metal? Explain your answer. Rod Y. Non-metals are poor heat conductors. Heat takes a longer time to travel through non-metals. 10. (a) Compare the properties of metals, non-metals and metalloids. Properties Metals Non-metals Metalloids Physical state at room temperature Solid except mercury Solid, liquid or gas Solid Appearance Shiny Dull Vary Malleability and ductility Malleable and ductile Brittle and nonductile Brittle and nonductile Melting and boiling points High except for mercury Low except for carbon Vary Electrical conductivity Good conductors Poor conductors Vary (b) How do malleability and ductility differ? Malleability is the ability of a material to get flattened under compression without breaking. Ductility is the ability of a material to get stretched under tension without breaking. 11. Give one use of metals, non-metals and metalloids each. (a) Metals: To make vehicles (b) Non-metals: To make fertilisers (c) Metalloids: To make electronic parts 94 ©Praxis Publishing_Focus On Science

5.3 Compounds 1. (a) What are compounds? Compounds are pure substances that have two or more elements combined chemically. (b) Give two examples of compounds. Water, carbon dioxide 2. The figures below show some compounds. Label the elements that make up each compound. State the ratio of the elements in each compound. (a) Water, H2 O Oxygen Hydrogen Hydrogen Ratio: Hydrogen : oxygen = 2 : 1 (b) Carbon dioxide, CO2 Oxygen Oxygen Carbon Ratio: Carbon : oxygen = 1 : 2 (c) Methane, CH4 Hydrogen Hydrogen Carbon Ratio: Carbon : hydrogen = 1 : 4 Chapter 5 Elements, Compounds and Mixtures 95 ©Praxis Publishing_Focus On Science

3. State the elements found in these compounds. Compounds Chemical formula Elements Calcium chloride CaCl2 Calcium, chlorine Potassium hydroxide KOH Potassium, oxygen, hydrogen Sodium carbonate Na2 CO3 Sodium, carbon, oxygen Ammonia NH3 Nitrogen, hydrogen Aluminium nitrate Al(NO3 ) 3 Aluminium, nitrogen, oxygen Copper(II) sulphate CuSO4 Copper, sulphur, oxygen 4. (a) Yuni is observing some sulphur powder and iron filings. (i) What are the colours of the sulphur powder and iron filings? Sulphur powder is yellow and iron filings are grey. (ii) What happens when a magnet is placed near the sulphur powder and iron filings separately? The sulphur is not attracted to the magnet. The iron filings are attracted to the magnet. (b) Yuni mixes the sulphur powder with the iron filings. What happens when a magnet is placed near the mixture? The grey iron filings are attracted to the magnet. (c) Yuni heats the mixture with a Bunsen burner until the colour of the mixture is changed. Iron and sulphur mixture Mineral wool Clamp (i) What will she observe after a while? The mixture turns into a black solid. (ii) When Yuni places a magnet near the product, nothing is attracted to the magnet. What is your conclusion of her experiment? A compound with different properties is formed. 96 ©Praxis Publishing_Focus On Science

5. Water is a compound. When it undergoes electrolysis, it breaks down into its constituent elements. The figure below shows the apparatus set-up for the electrolysis of water. Two different gases are collected. + - Dry cells Electrode Gas A Gas B Electrode Distilled water + a few drops of sulphuric acid (a) When gas A is tested with a glowing splinter, the splinter reignites. What is gas A? Oxygen (b) When gas B is tested with a burning splinter, it gives out a pop sound. What is gas B? Hydrogen (c) (i) What is the ratio of the elements that make up water based on the experiment? Oxygen : hydrogen = 1 : 2 (ii) Does this ratio change when this experiment is carried out in mountains? Why? No. The elements in a compound combine in a fixed proportion. (d) What happens when water undergoes electrolysis? Water breaks down into the elements that make up water, which are oxygen and hydrogen. 6. Tick (✓) the correct statements. (a) A compound is formed when some sodium is added to water. ✓ (b) When some carbon is burned in oxygen, a compound, carbon dioxide is formed. ✓ (c) A compound can be broken down into its constituent elements by hammering it with a hammer. (d) The properties of the elements that make up a compound and the properties of the compound are different. ✓ (e) The ratio of carbon to oxygen in carbon dioxide changes due to the temperature. (f) The ratio of elements that make up a compound is fixed. ✓ Extra Info Water electrolysis i Chapter 5 Elements, Compounds and Mixtures 97 ©Praxis Publishing_Focus On Science