Science (English Medium) कक्षा १२ - CBSE Important Questions for Physics

A ray of monochromatic light propagating in the air is incident on the surface of the water. Which of the following will be the same for the reflected and refracted rays?

According to Huygens’s principle, the amplitude of secondary wavelets is ______.

Plot a graph showing variation of de Broglie wavelength λ versus `1/sqrtV` , where V is accelerating potential for two particles A and B, carrying the same charge but different masses m₁, m₂ (m₁ > m₂). Which one of the two represents a particle of smaller mass and why?

Write three characteristic features in photoelectric effect that cannot be explained on the basis of wave theory of light, but can be explained only using Einstein's equation.

The graph shows the variation of stopping potential with frequency of incident radiation for two photosensitive metals A and B. Which one of the two has higher value of work-function? Justify your answer.

How does one explain the emission of electrons from a photosensitive surface with the help of Einstein's photoelectric equation?

The wavelength λ of a photon and the de-Broglie wavelength of an electron have the same value. Show that energy of a photon in (2λmc/h) times the kinetic energy of electron; where m, c and h have their usual meaning.

Describe briefly how the Davisson-Germer experiment demonstrated the wave nature of electrons.

An electron is accelerated from rest through a potential V. Obtain the expression for the de-Broglie wavelength associated with it ?

Define the terms (i) ‘cut-off voltage’ and (ii) ‘threshold frequency’ in relation to the phenomenon of photoelectric effect.

Using Einstein’s photoelectric equation shows how the cut-off voltage and threshold frequency for a given photosensitive material can be determined with the help of a suitable plot/graph.

Show on a graph the variation of the de Broglie wavelength (λ) associated with an electron, with the square root of accelerating potential (V) ?

Write two characteristic features observed is photoelectric effect which supports the photon pictures of electromagnetic radiation ?

Draw a graph between the frequency of incident radiation (υ) and the maximum kinetic energy of the electrons emitted from the surface of a photosensitive material state clearly how this graph can be used to determine (i) Planck’s constant and (ii) work function of the material.

Plot a graph to show the variation of stopping potential with frequency of incident radiation in relation to photoelectric effect.

How does one explain the emission of electrons from a photosensitive surface with the help of Einstein’s photoelectric equation? 

The stopping potential in an experiment on photoelectric effect is 1.5V. What is the maximum kinetic energy of the photoelectrons emitted? Calculate in Joules.

Answer the following question.
Why is the wave theory of electromagnetic radiation not able to explain the photoelectric effect? How does a photon picture resolve this problem?

1. Calculate the energy and momentum of a photon in a monochromatic beam of wavelength 331.5 nm.
2. How fast should a hydrogen atom travel in order to have the same momentum as that of the photon in part (a)?

Name the factors on which photoelectric emission from a surface depends.

An electron is accelerated from rest through a potential difference of 100 V. Find:

1. the wavelength associated with
2. the momentum and
3. the velocity required by the electron.