Download Magnetism - WordPress.com

Magnetism:





The objects which attract or repel magnetic materials are called magnets.
Magnets have two poles: North (N) and South(S)
When we hang a magnet on a string, the end shows the North direction of Earth is called the Northseeking pole (North pole) and the end shows the South direction of Earth is called the South-seeking
pole (South pole).
Like poles repel each other whereas the Unlike poles attract each other.
Making magnets:
Magnets can be made from steel or iron by the following methods;
1. Stroking Method:
- Steel is used in this method
- end of the steel bar, where the North of the
magnet starts to stroke becomes North pole.
2. Electricity Method:
- iron nail, copper wire and battery are used in this method.
- as the current passes through the coil of wire, the iron nail
becomes magnetised. This is called an Electromagnet.
- The strength of the electromagnet can be increased by:
i. increasing the number of turns of the coil
ii. Increasing the current or voltage.

Destroying Magnetism:
A magnetised steel or iron can be demagnetised by the following methods;
1. Hammering
2. Heating
3. Passing ac current through the iron nail.

Magnetic field:
The space around a magnet where the magnet can
attract or repel magnetic materials is called Magnetic
field.
The Magnetic field lines:
- show the direction of the magnetic force at each
point.
- never cross each other.
- are more near the poles of the magnet. (So that
the poles have more magnetic strength)
- start from North pole and end at South pole.
Like poles

Compass needle:
A compass needle shows the North-South
direction. It’s needle is a magnet which aligns
in the North-South direction.

Investigating a Magnetic field:
we can use a compass needle.
Unlike Poles
To draw a magnetic field
Questions:
1. What are magnets?
The substances having the property of attracting iron objects are known as magnets.
2. What are magnetic substances?
The substances that are attracted by magnet are called as magnetic substances.
eg. Iron, Steel, Cobalt and Nickel.
3. What is meant by poles of a magnet?
The end of a magnet where the magnetic property is strongest is called poles of a magnet.
4. What happens when a suspended bar magnet is left more freely?
The freely suspended bar magnet points in the North – South direction when it comes to rest.
5. What is meant by a) North pole b) South pole
North Pole: The end of the magnet that point north is called North pole.
South Pole: The end of the magnet that point south is called south pole.
6. Like poles repel each other.
Unlike poles attract each other.
7. What is a magnetic compass?
The magnetic compass is used to find the direction.
8. What is a magnetic field?
The area around the magnet where it pushes or pulls is called a magnetic field.
9. How can you find the pattern of the magnetic field around a magnet? (description pg 54,55)
 Iron filings method
 Magnetic compass method.
10. The lines that show the shape of the magnetic field are called lines of magnetic force.
11. Draw the magnetic field around a bar magnet.
12. Copy the boxes shown below, and then draw lines between them to make correct statements.
A steel core
makes an electromagnet
stronger.
Adding more coils of
wire
is like the one found around a
bar magnet.
An electromagnet’s
magnetic field
the stronger the field of the
electromagnet.
A smaller current
through coils
makes an electromagnet
permanent.
The more paper clips
attracted
makes an electromagnet
weaker.
13. What are the ways of making an electromagnet stronger?
 Use a bigger core
 Put more turns of wire on the coil.
 Use an iron core inside the coil.
14. What are the advantages of electromagnets?
Electromagnets can be easily magnetized and demagnetized.
15. How would you label pole 1?
16. How would you label pole 2? Why?
17. How would you label poles 5 and 6? Why?
18. How could you use iron filings to tell which of two bar magnets is stronger?
19. What generalization can you make about the reaction between like poles?
20. What generalization can you make about the reaction between unlike poles?
21. The magnetic field is strongest near (the poles/the center) of a bar magnet.
22. Materials that can become magnetized include steel and (copper/iron).
23. The needle of a compass lines up with Earth’s magnetic field and points to (Earth’s poles/Earth’s
equator).
24. Magnetic field lines that curve toward each other show (repulsion/attraction).
Directions: Match the following terms with the correct descriptions below.
25. imaginary lines of force around a magnet
26. a force created through a magnetic field
27. a magnetic needle that is free to turn
28. a current-carrying wire wrapped around an iron core
(a) compass
(b) electromagnet
(c) magnetism
(d) magnetic field