Science (English Medium) इयत्ता १२ - CBSE Question Bank Solutions for Physics

Two circular loops of equal radii are placed coaxially at some separation. The first is cut and a battery is inserted in between to drive a current in it. The current changes slightly because of the variation in resistance with temperature. During this period, the two loops _______________ .

A bar magnet is moved along the axis of a copper ring placed far away from the magnet. Looking from the side of the magnet, an anticlockwise current is found to be induced in the ring. Which of the following may be true?
(a) The south pole faces the ring and the magnet moves towards it.
(b) The north pole faces the ring and the magnet moves towards it.
(c) The south pole faces the ring and the magnet moves away from it.
(d) The north pole faces the ring and the magnet moves away from it.

Is it always true that for two sources of equal intensity, the number of photons emitted in a given time are equal?

What is the speed of a photon with respect to another photon if (a) the two photons are going in the same direction and (b) they are going in opposite directions?

A hot body is placed in a closed room maintained at a lower temperature. Is the number of photons in the room increasing?

In an experiment on photoelectric effect, a photon is incident on an electron from one direction and the photoelectron is emitted almost in the opposite direction. Does this violate the principle of conservation of momentum?

It is found that yellow light does not eject photoelectrons from a metal. Is it advisable to try with orange light or with green light?

It is found that photosynthesis starts in certain plants when exposed to sunlight, but it does not start if the plants are exposed only to infrared light. Explain.

The threshold wavelength of a metal is λ₀. Light of wavelength slightly less than λ₀ is incident on an insulated plate made of this metal. It is found that photoelectrons are emitted for some time and after that the emission stops. Explain.

Planck's constant has the same dimensions as

Two photons of 

Let n_r and n_b be the number of photons emitted by a red bulb and a blue bulb, respectively, of equal power in a given time.

The equation E = pc is valid

The work function of a metal is hv₀. Light of frequency v falls on this metal. Photoelectric effect will take place only if

Light of wavelength λ falls on a metal with work-function hc/λ₀. Photoelectric effect will take place only if

When stopping potential is applied in an experiment on photoelectric effect, no photoelectric is observed. This means that