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

A capacitor acts as an infinite resistance for ______.

An AC source producing emf ε = ε₀ [cos (100 π s⁻¹)t + cos (500 π s⁻¹)t] is connected in series with a capacitor and a resistor. The steady-state current in the circuit is found to be i = i₁ cos [(100 π s⁻¹)t + φ₁) + i₂ cos [(500π s⁻¹)t + ϕ₂]. So,

The peak voltage of a 220 V AC source is

An AC source is rated 220 V, 50 Hz. The average voltage is calculated in a time interval of 0.01 s. It

A parallel-plate capacitor of plate-area A and plate separation d is joined to a battery of emf ε and internal resistance R at t = 0. Consider a plane surface of area A/2, parallel to the plates and situated symmetrically between them. Find the displacement current through this surface as a function of time.

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

The AC voltage across a resistance can be measured using

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.