Electric Charges and Fields — Physics STD 12 Science — Question

An electron of charge ‘e’ coulomb passes through a potential difference of V  volts. Its energy in ‘joules’ will be

(a) V/e

(b) eV

(c) e/V

(d) V

Two thin lenses, one of focal length + 60 cm and the other of focal length – 20 cm are put in contact. The combined focal length is

(a) + 15 cm

(b) – 15 cm

(c) + 30 cm

(d) –30 cm

Assertion :  The refractive index of diamond is  and that of liquid is . If the light travels from diamond to the liquid, it will totally reflected when the angle of incidence is 30^o.

Reason    :  μ =  where m is the refractive index of diamond with respect to liquid.

(a) If both assertion and reason are true and the reason is the correct explanation of the assertion.

(b) If both assertion and reason are true but reason is not the correct explanation of the assertion.

(c) If assertion is true but reason is false.

(d) If assertion is false but reason is true.

Assertion :   A compass needle when placed on the magnetic north pole of the earth rotates in vertical direction.

Reason     : The earth has only horizontal component of its magnetic field at the north poles.

(a) If both assertion and reason are true and the reason is the correct explanation of the assertion.

(b) If both assertion and reason are true but reason is not the correct explanation of the assertion.

(c) If assertion is true but reason is false.

(d) If the assertion and reason both are false.

When the intensity of a light source is increased:

1. The number of photons emitted by the source in unit time increases.
2. The total energy of the photons emitted per unit time increases.
3. More energetic photons are emitted.
4. Faster photons are emitted.

Ray optics is valid when characteristic dimensions are:

Electric bulb 50 W-100 V glowing at full power are to be used in parallel with battery 120 V, 10 W. Maximum number of bulbs that can be connected so that they glow in full power is

(a) 2

(b) 8

(c) 4

(d) 6

The force between two charges 0.06 m apart is 5 N. If each charge is moved towards the other by 0.01 m, then the force between them will become

(a) 7.20 N

(b) 11.25 N

(c) 22.50 N

(d) 45.00 N

In Young’s double slit experiment, the central bright fringe can be identified

(a) By using white light instead of monochromatic light

(b) As it is narrower than other bright fringes

(c) As it is wider than other bright fringes

(d) As it has a greater intensity than the other bright fringes