SUBTOPIC 7.3 MAGNETISM

CHAPTER 7.3
MAGNETISM

Prepared by Cikgu Husrita

Attracts magnetic materials Has poles (north pole
such as iron, nickel and cobalt and south pole

PROPERTIES Freely suspended
OF A magnet shows north-

MAGNET south direction

• MAGNETIC FIELD

1. Magnets are made of iron, steel, cobalt and nickel

2. Magnets exit naturally in the form of lodestones

3. A magnet has a magnetic field around it

4. A magnetic field is the region around a magnet where its magnetic forces
act

The characteristic of magnetic field:

i. Magnetic field lines never meet or cross with one another
ii. Magnetic field lines of like poles repel each other
iii. Magnetic field lines of different poles attract each other
iv. There is an empty space without any magnetic field lines at

the central point between two like poles. This point is known
as the neutral point
v. The closer the magnetic field lines, the stronger the magnetic field
vi. Magnetic filed lines are closer near the poles

SHAPE OF A MAGNETIC FIELD

What is the shape and direction of the lines of force in the
magnetic field around a bar magnet?

strongest N strongest
field
S field
at poles
at poles

weakest field further
away from poles

Where is the magnetic field strongest?

MAGNETIC
FIELD LINE

XX X is the neutral point
X where the empty

space does not have
any magnetic field

ELECTROMAGNET

Is a type of magnet that has temporary
magnetic effect when electric current

flows through it

1. When current flows through an iron nail, it
becomes an electromagnet

2. The iron nail can attract small pieces of
metal

3. The iron nail will lose its magnetism when
the current is disconnected

4. Its strength increases as the current
increases

ELECTROMAGNET

1. Electromagnetism works on the principle that an electric current flowing through a wire
produces a magnetic field

2. The characteristic of an electromagnet
i. is a type of magnet where its magnetic field is produced by the flow of an electric
current
ii. will disappear when the current ceases / OFF

iii. can be described as a temporary magnet that runs on electricity
iv. form a circle with the conducting wire as its centre
v. the strength can be change by changing the amount of electric current that flows

through it
vi. Right-hand-grip rule determines the direction of the magnetic field of the straight

wire that transports current

Right-hand-grip rule;

Right hand = grip the wire
Thumb = direction of current flow

Finger will curl = field lines

ELECTROMAGNET

The magnetic field pattern
that formed depends on the
shape of the conductor used.

The magnetic lines that are
produced by a straight wire

ELECTROMAGNET

The magnetic field pattern that formed
depends on the shape of the conductor

used.

The magnetic lines that are
produced by a coil wire

MAGNETIC FIELD IN A SOLENOID

Soft iron
core

SN

Hold the solenoid with fingers curled around the
solenoid along the direction of the current. The thumb

will point to the end that is the North pole.

ELECTROMAGNET

The magnetic lines that
are produced by a
solenoid

How to increase the strength of
the magnetic field of an
electromagnet ???
• Increase the number of turns of

coiled wire (solenoid)
• Increase the electric current

that flows through the coiled
wire

APPLICATION OF MAGNET AND ELECTROMAGNETS IN OUR
DAILY LIFE

The needle of the compass The crane uses the The credit card has an
is a weak magnet that electromagnet to pick up electromagnetic strip used
iron and steel scrap metals
shows the direction of the for storing data
pole

APPLICATION OF MAGNET AND ELECTROMAGNETS IN OUR
DAILY LIFE

The magnetic lock on doors The electric bell uses
uses an electromagnet to electromagnet to produce
lock the doors automatically
the ringing sound