Question

1. Specific resistance of a wire depends upon

(a) Length of the wire
(b) resistance of the wire

(c) area of cross section
(d) material of the wire


2. Which of the following statement is/are false?

(i) An electric motor converts mechanical energy into electrical energy



(ii) An electric generator works on the principle of electromagnetic induction



(iii) In a DC electric motor a pair of split rings is used as commutator.


(iv) Induced current will appear in such a direction that it opposes the change that produced it.



(a) i, ii (b) ii, iii, iv (c) i only (d) None



3. A copper ring having a cut such as not to form a complete loop is held horizontally and a bar magnet is dropped through the ring with its length along the axis of the ring. Then the acceleration of the falling magnet is (neglect air friction)

(a) g

(b) less than g
(c) more than g
(d) 0


Solve all questions .

★ Explanation needed ★ ​

Answer 1

1. Specific resistance of a wire depends upon

(a) Length of the wire

(b) resistance of the wire

(c) area of cross section

(d) material of the wire

Option d).

Because resistivity (specific resistance) is a property of material, so it is generally independent of length, area and resistance.

2. Which of the following statement is/are false?

(i) An electric motor converts mechanical energy into electrical energy

(ii) An electric generator works on the principle of electromagnetic induction

(iii) In a DC electric motor a pair of split rings is used as commutator.

(iv) Induced current will appear in such a direction that it opposes the change that produced it.

Option c) - only i is correct one.

An electric motor converts mechanical energy into electrical energy

3. A copper ring having a cut such as not to form a complete loop is held horizontally and a bar magnet is dropped through the ring with its length along the axis of the ring. Then the acceleration of the falling magnet is (neglect air friction)

Option a) - g

Induced current will not produce.

So no opposition, hence it will be in a situation of free fall, so g.

Answer 2

The specific resistance of a conducting wire depends on the nature of material of the body and and indepndent of shape and size of the body.

(a) False

An electric motor converts electrical energy into mechanical energy. As current carrying coil is placed in a magnetic field, it experiences a force due to which it starts rotating.

(b) True  

An electric generator works on the principle of electromagnetic induction. When the coil is rotated by external mechanical forces in a magnetic field, the magnetic flux through the coil changes. This creates an induced emf in the coil and hence induced current flows.

(c) True

The field at the center of a long solenoid carrying current will be parallel straight lines. This can also be verified by Right hand thumb Rule.

(d) False

Live wire has red insulation cover, whereas earth wire has green insulation colour in the domestic circuits.

As the ring is not continuous, the emf will generate in the ring but due to incomplete circuit, no current will flow. As no current flows, no magnetic field will generate and the motion of the bar magnet will not be opposed.

Thus, the bar magnet will continuously fall freely under the gravity only.

Therefore, the acceleration of the falling magnet will be equal to the acceleration due to gravity g.