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## Chapter: 9th Science : Physics : Magnetism and Electromagnetism

Science : Physics : Magnetism and Electromagnetism : Book Back Important Questions, Answers, Solutions : I. Choose the correct answer, II. Fill in the blanks, III. State whether true or false. If false, correct the statement, IV. Match the following, V. Assertion and reason type questions

### TEXT BOOK EXERCISES

I. Choose the correct answer :

1. Which of the following converts electrical energy into mechanical energy?

(a) Motor

(b) Battery

(c) Generator

(d) Switch

2. Transformer works on ――― .

(a) AC only

(b) DC only

(c) Both AC and DC

3. The part of the AC generator that passes the current from the armature coil to the external circuit is

(a) field magnet

(b) split rings

(c) slip rings

(d) brushes

4. The unit of magnetic flux density is

(a) Weber

(b) weber/metre

(c) weber/metre2

(d) weber.metre2

II. Fill in the blanks :

1. The SI Unit of magnetic field induction is Tesla .

2. Devices which is used to convert high alternating current to low alternating current is transformers

3. An electric motor converts electrical energy into mechanical energy .

4. A device for producing electric current is generator .

III. Match the following :

1. Magnetic material - a) Oersted

2. Non-magnetic material - b) Iron

3. Current and magnetism - c) Induction

4. Electromagnetic induction - d) Wood

5. Electric generator - e) Faraday

Answer: 1-b, 2-d, 3-a, 4-e, 5-c

1. Magnetic material - Iron

2. Non-magnetic material - Wood

3. Current and magnetism - Oersted

5. Electric generator - Induction

### IV. State whether true or false. If false, correct the statement:

1. A generator converts mechanical energy into electrical energy.

2. Magnetic field lines always repel each other and do not intersect.

3. Fleming’s Left hand rule is also known as Dynamo rule.

Correct statement: Fleming's Left hand rule is also known as motor rule.

4. The speed of rotation of an electric motor can be increased by decreasing the area of the coil.

Correct statement: The speed of rotation of an electric motor can be increased by increasing the area of the coil.

5. A transformer can step up direct current.

Correct statement: A transformer can step up alternating current (AC).

6. In a step down transformer the number of turns in primary coil is greater than that of the number of turns in the secondary coil.