Temporary and Permanent Magnets

Q.

List the methods used for magnetisation

Q.

What is magnetic induction? Describe in detail how a steel needle can be magnetized by induction.

Q.

The magnet used in a magnetic compass is:

1. electromagnet

2. permanent magnet

3. temporary magnet

4. none of the above

Q.

For magnetizing a magnetic substance, the single-touch method is used.

1. True
2. False

Q.

………precedes attraction in magnetization.

Q.

Assertion(A): When an iron piece is magnetised, its length slightly increases.

Reason(R): The closed molecular chains break down and all molecules align themselves in the direction of external magnetic field.

1. A and R are true and R is the correct explanation of A.

2. A and R are true but R is not the correct explanation of A.

3. A is true but R is false.

4. Both A and R are false.

Q. Write two characteristics of a material to constructes a permanent magnet. Give two examples of such materials.

Q.

What role does the magnetic induction play in the attraction of a piece of a soft iron bar by a magnet?

Q.

……….precedes attraction in magnetisation.

Q. By removing a permanent magnet, the induced magnetic field is:

1. finished just after.
2. not finished for a long time.
3. finished after some time.
4. not charged.

Q. The following properties belong to which magnet?
a. Made of soft iron.
b. Strength of magnetic field can be changed.
c. Strong magnetic field but can be easily demagnetized
d. Polarity can be reversed

1. Permanent magnet
2. Bar magnet
3. Electro-magnet
4. Horse-shoe magnet

Q. Which of the following statements are true for permanent magnet?
a. It is made of steel
b. It has a strong magnetic field which can be altered
c. Polarity cannot be reversed
d. Used in electric meters, magnetic compasses etc

1. a, c and d
2. All of the above
3. a, b and c
4. b, c and d

Q. The metallic pointer (needle) of a plotting compass gets deflected only when it is placed near a bar magnet because the pointer has

1. Electromagnetism
2. Static magnetism
3. Induced magnetism
4. Permanent magnetism

Q. A magnet can be demagnetised by

1. Hammering the magnet
2. Putting it in the water
3. Cooling it
4. Putting it in contact with iron

Q. With the help of a metal can be turned into a magnet, temporarily.

1. electricity
2. heating
3. pressing
4. non-metal

Q.

Q. What is magnetic induction ? Describe in detail how a steel needle can be magnetised by induction.

Q.

Write two differences between a permanent magnet and a temporary magnet.

Q.

What are magnetic keepers?

Q. Permanent magnets are formed because of heating effect of electricity.

1. True
2. False

Q. A permanent magnet can be made strong by passing current through an insulated coil wound over it .

1. True
2. False

Q. What are permanent magnets? What is an efficient way of preparing a
permanent magnet? Write two characteristic properties of materials which are required to select them for making permanent magnets.

Q. When a powerful magnet is held near a piece of soft iron, the latter changes to magnet on account of the phenomenon of :

1. magnetic induction
2. magnetic conduction
3. magnetic attraction
4. none of the above

Q. Mention two characteristics of a material that can be used for making permanent magnets.

Q. Tick the most appropriate answer.
Temporary magnets are made of

1. Soft iron
2. Steel
3. Stainless Steel
4. Copper

Q. State three differences between the temporary and permanent magnets.

Q. Steel is used for making permanent magnet because :

1. energy loss is minimum
2. density of steel is more
3. residual magnetism of steel is more
4. due to external magnetic field the magnetism does not destroy easily

Q. State if the following statements are true or false. Correct the statement if it is false.
Temporary magnets are made of cobalt.

1. True
2. False

Q. A permanent magnet

1. Attracts all substances
2. Attracts only magnetic substances
3. Attracts non-magnetic substances and repels magnetic substances
4. Attracts magnetic substances and repels all non-magnetic substances

Q. Explain how a strong permanent magnet can be made.