Current Electricity — Physics STD 12 Science — Question

The earth's magnetic induction at a certain point is 7 × .  This is to be annulled by the magnetic induction at the centre of a circular conducting loop of radius 5 cm. The required current in the loop is

(a) 0.56 A

(b) 5.6 A

(c) 0.28 A

(d) 2.8 A

Which error is removed when the known and unknown resistances are interchanged in a Meter Bridge?

Figure shows a charge q placed at the centre of a hemisphere. A second charge Q is placed at one of the positions A, B, C and D. In which position(s) of this second charge, the flux of the electric field through the hemisphere remains unchanged?

1. A
2. B
3. C
4. D

Two statements are given-one labelled Assertion (A) and the other labelled Reason (R). Select the correct answer to these questions from the codes (a), (b), (c) and (d) as given below.
Assertion (A): The kinetic energy of a charged particle moving in a uniform magnetic field does not change. Reason (R): In a uniform magnetic field no force acts on the charge particle.

A small object is placed 10 cm infront of a plane mirror. If you stand behind the object 30 cm from the mirror and look at its image, the distance focused for your eye will be

(a) 60 cm

(b) 20 cm

(c) 40 cm

(d) 80 cm

In the circuit shown in figure, the heat produced in 5 ohm resistance is 10 calories per second. The heat produced in 4 resistance is

(a) 1 cal / sec

(b) 2 cal/sec

(c) 3 cal / sec

(d) 4 cal/sec

The number of revolutions per second made by an electron in the first Bohr orbit of hydrogen atom is of the order of 3

(a)

(b)

(c)

(d)

If two wires having resistance R and 2R. Both joined in series and in parallel then ratio of heat generated in this situation, applying the same voltage,

(a) 2 : 1

(b) 1 : 2

(c) 2 : 9

(d) 9 : 2

Magnetic field intensity at the centre of coil of 50 turns, radius 0.5 m and carrying a current of 2 A is

(a) 0.5

(b) 1.25

(c) 3

(d) 4