# Samacheer Kalvi 9th Science Book Back Answers Chapter 12

## Samacheer Kalvi 9th Science Book Back Question and Answers:

Samacheer Kalvi 9th Standard Science Book Back 1 Mark and 2 Mark Question & Answers PDF uploaded and available below. Class 9 New Syllabus 2022 to 2023 Book Back Questions & Answers/solutions available for both English and Tamil Medium. Class 9 std Science Book Term 2 Chapter 3 – Magnetism and Electromagnetism Answers/Solutions Guide are uploaded on this page. In the new 9th Science syllabus Term 1, Term 2, and Term 3 are combined into a single book. The 9th standard Science Book consists of 27 Units. All 27 chapters of Term 1st, 2nd, 3rd Science Book Back One, and Two Mark Solutions are given below.

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### 9th Science Book Back Term 2 Chapter 3 Solutions Guide PDF:

Samacheer Kalvi 9th Science Subject 1 Mark and 2 Mark Solutions Guide PDF available below. Click the Download option to download the book back 1 Mark & 2 Mark questions and answers. Take the printout and use it for exam purposes.

### Electromagnetism – Book Back Answers

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. An electric generator converts.
a) electrical energy into mechanical energy.
b) mechanical energy into heat energy
c) electrical energy into electrical energy
d) mechanical energy into electrical energy.

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. Transformer works on
a) AC only
b) DC only
c) both AC and DC
d) AC not effectively then DC

5. The unit of magnetic flux density is
a) Weber
b) weber/metre
c) weber/meter2
d) weber, meter2

II. Fill in the blanks:

1. The SI unit of magnetic field induction is teslas T
2. No force acts in a current carrying conductor when it is parallel to the magnetic field.
3. Device which is used to convert high alternating current to low alternating current transformer
4. An electric motor converts electrical energy into mechanical energy
5. 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                d) wood
5. Electric generator              e) Faraday
Ans: 1-b; 2-d; 3-a; 4-e; 5-c

IV. True or False

1. A generator converts mechanical energy into electrical energy. –True
2. Magnetic field lines always repel each other and do not intersect. –True
3. Fleming’s left hand rule is also known as Dynamo rule. –False
4. The speed of rotation of an electric motor can be increased by decreasing the area of the coil. –False
5. A transformer can step up direct current. –False
6. In a step down transformer the number turns in primary coil is greater than that of the number of turns in the secondary coil. –True

V. Short Answer & Questions:

1. State Fleming’s Left Hand Rule.

The law states that while stretching the three fingers of left hand in perpendicular manner with each other, if the direction of the current is denoted by middle finger of the left hand and the second finger is for direction of the magnetic field then the thumb of the left hand denotes the direction of the force or movement of the conductor.

2. Define magnetic flux density.
The number of magnetic field lines crossing unit area kept normal to the direction of field lines is called magnetic flux density.

3. List the main parts of an electric motor.
Permanent magnet, Commutator, carbon brushes, coil, DC power supply.

4. Draw and label the diagram of an AC generator.

5. State an important advantage of ac over dc.
A transformer cannot be used with the direct current (DC) source because of current in primary coil is Constant (te. DC). Then there will be no change in the number of magnetic field lines 1inJed with the secondary coil and hence no emf will be induced in the secondary coil.

6. Differentiate step up and step down transformer.
Step up transformer: The transformer used to change a low alternative voltage to a high alternating voltage is called a step up transformer. Ie. (Vs > Vp) . In a step up transformer, the number of turns in the secondary coil is more than the number of turns in the primary coil (Ns>Np).
Step down transformer: The transformer used to change a high alternating voltage to a low alternating voltage is called a step down transformer (Vs < Vp). In a step down transformer, the number of turns in the secondary coils are less than the number of turns in the primary coil (Ns<Np).

7. A portable radio has a built in transformer so that it can work from the mains instead of batteries. Is this a step up or step down transformer?
Step down transformer: The transformer used to charge a high alternating voltage to a low alternating voltage is called a step down transofermer (Vs<Vp). In a step down transformer, the number of turns in the secondary coils are less than the number of turns in the primary coil (Ns<Np).

8. Two coins A and B of insulated wire are kept close to each other. Coil A is connected to galvanometer. While coil B is connected to a battery through a key. What would happen if
i) a current is passed through coil B by plugging the key?
ii) The current is stopped by removing the plug from the key?
When the switch is put ‘on’, at that instant, there is a deflection in the galvanometer. Likewise, when the switch is put ‘off’, again there is a deflection but in the opposite direction. This proves the generation of current.

9. State Faraday’s laws of electromagnetic induction.
Whenever there is a change in the magnetic flux linked with a closed-circuit an emf is produced and the amount of emf induced varies directly as the rate at which the flux changes. This emf is known as induced emf and the phenomenon of producing an induced emf due to a change in the magnetic flux linked with a closed circuit is known as electromagnetic induction.

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