Exercise 1. Choose the correct alternatives: (a) Whichof the following is a natural magnet? (i) limestone (ii) nickel (iii) loadstone (iv) electro1nagnet (b) To which wire in a home's electrification system is the switch connected? (i) neutral wire (iii) fuse wire (ii) earth wire (iv) live wire (c) Which one of the following figures gives evidence of geomagnetism? (I) (II) (III) (IV) (i) I (ii) II (iii) III (iv) IV ( d) "Earthing prevents the electrical equipment from being damaged or destroyed. " How is the earthing done in household wiring? (i) A wire is buried in the earth. (ii) A green-coloured wire is buried in the earth. (iii) A wire is taken from the plug and connected to the earth. (iv) Earth wire is taken frmn every electrical equipment and buried in the earth. 2. Differentiate between: a. natural magnet and artificial n1agnet Science an d Technology, Grade 6 247
b. plug and socket c. live wire and neutral wire 3. Give reasons: a. The magnet gets demagnetized while harmnering. b. The angle of inclination or the angle of dip at the geomagnetic poles is 90°. c. Different coloured wires are used in domestic wiring. d. The fuse is always connected in phase or live wire in domestic wiring. 4. Answer the following questions: a. What are the conditions for the demagnetization of a magnet? Explain any one of them in brief. b. Explain, with a diagram, the molecular theory of magnetism. c. Write down any three applications of the magnet. d. What is terrestrial magnetism? e. Write any three applications of terrestrial magnetism. f. What is household electrification? Write down the characteristics of neutral and phase wires used in household electrification. g. "Magnetization of magnetic materials in nature is the effect of terrestrial rnagnetism." Justify this statement with examples. h. Write down the steps of wiring a plug. L What is earthing? \/\Thy is earthing necessary in domestic wiring? J. "The orientation of magnetic molecules determines the condition of magnet and magnetic substance." Are the magnetic and non-magnetic propertiesof a substance interchangeable according to the above statement? Justify. k. Is there a connection between magnets and electricity? Explain their connection with any activity. 248 Science and Techn ology, Grade 8
5. Solve the following numerical problems: a. The electric nrnter in Bhawana's house records 15 units of consumption of electricity in 15 days. Calculate the average monthly electricity bill of Bhawana's house if the cost of electricity is Rs. 9.5 per unit. (Ans: Rs 1425) b. If 8 bulbs each of power 25 Ware installed in a house used for 4 hours 40 minutes daily, calculate the total electricity consumption, in units, in a day. (Ans: 0.0932 units) c. The sub-1neter in Sharmila's room records 8.5 units of electricity in a month. If there is only one electric bulb of power 65 Win her room, calculate the average duration for which theelectric bulb is used in a day. (Ans: 4.353 hrs.) d. In a certain place, the municipality installed 14 street lights each rated 1500 W. These street lights are used for 6.5 hours daily on average. If the municipality has to pay the electricity bill at the rate of Rs 12.50, calculate the monthly bill paid by the municipality to the electricity authority for using these street lights. (Ans: Rs 51187.50) Science an d Technology, Grade 6 249