Magentismand Electricity - ppt useful for grade 6,7 and8 Content Magnets Electromagnets Electric bell bar magnet permanent magnet Electromagnetism Materials used to make a magnet lodestone etc Hope u guys like it

1. .
Magnetism and Electricity

2. Magnetite
HISTORY OF MAGNETISM

3. What are Natural Magnets?
• The naturally occurring materials which
have the property of attracting iron.
• These are weak magnets.
What are Artificial Magnets?
• They are made of materials like iron,
cobalt and nickel which can be easily
magnetized.
• They are strong magnets.
• They can be made in different shapes and
sizes.

4. Artificial Magnets

5. What is magnetism?
• Magnetism is a force of attraction or repulsion
that acts at a distance. It is due to magnetic
field, which is caused by moving electrically
charged particles or is inherent in magnetic
objects such as a magnet.

7. Why does a magnet suspended
freely comes to rest only in North-
South direction?
This is because
the earth
behaves like a
huge bar
magnet.

8. Earth’s Magnetic Field

9. http://phet.colorado.edu/en/simulation/magnet-
and-compass

10. Magnetic lines of force
• The imaginary lines which represent the
direction of magnetic field, are known as
magnetic lines of force.
• Magnetic lines of force are closed curves.
Outside the magnet their direction is from
north pole to south pole and inside the
magnet these are from south to north pole.

12. • When electric current is passed through a
conductor, a magnetic field is produced
around it
• The branch of physics which deals with
the magnetic effect of electric current is
called electromagnetism.
What is electromagnetism?

13. Electromagnet
• An electromagnet is a solenoid with a soft iron
core.
• When using iron, the magnet is temporary.
• When using steel, the magnet is permanent

14. What is an electromagnet ?
• An electromagnet is a solenoid
with a soft iron core.

15. The strength of an electromagnet depends on:
Number of turns in its coils &
Amount of current passing through the coil
USES OF ELECTROMAGNET
They are used in appliances such as electric motors,
electric fans and electric bells.
• They are used in lifting heaving loads of iron and scrap
and are also used in cranes to lift vehicles.
• They are used to deflect beams of electrons in TVs.
• They are used to separate iron ores from impurities in
mining industries.
• They are used in relays in telephone exchanges and in
computers.
• They are used by doctors to cure certain diseases.

16. Bar Magnet Electromagnet
• Made of steel • Made of soft iron
• Poles cannot be reversed • Poles can be reversed
• It produces a permanent
magnetic field
• It produces a temporary
magnetic field
• Strength of magnetic field
cannot be changed
• Strength of magnetic field
can be changed
• Does not need electric
current to act as a magnet
• Requires electric current to
act as an electromagnet
Comparison between a Bar Magnet
and an Electromagnet

18. PARTS OF AN ELECTRIC BELL
An electric bell includes:
U- shaped electromagnet (it is made of soft iron)
Armature (soft iron bar which faces the poles of the magnet)
Contact spring
Contact adjustment screw
Hammer
Gong
Switch
Battery

19. WORKING
When the switch is pressed the circuit is complete.
The current begins to flow through the
electromagnet.
The magnet gets magnetised and attracts the
armature.
The armature gets attracted to the magnet and
due to the motion of the armature towards the
poles of the solenoid and the hammer moves and
strikes the gong, thereby causing the bell to ring.