Science (English Medium) कक्षा १२ - CBSE Important Questions

• Assertion (A): In Young's double slit experiment all fringes are of equal width.
• Reason (R): The fringe width depends upon the wavelength of light (λ) used, the distance of the screen from the plane of slits (D) and slits separation (d).

In Young's double-slit experiment, the screen is moved away from the plane of the slits. What will be its effect on the following?

1. The angular separation of the fringes.
2. Fringe-width.

Using Huygens's construction, show how a plane wave is reflected from a surface. Hence verify the law of reflection.

A proton and an α-particle have the same de-Broglie wavelength Determine the ratio of  their speeds.

Draw a plot showing the variation of photoelectric current versus the intensity of incident radiation on a given photosensitive surface.

Why photoelectric effect cannot be explained on the basis of wave nature of light? Give reasons.

point out any two characteristic properties of photons on which Einstein’s photoelectric equation is based ?

Briefly explain the three observed features which can be explained by Einstein’s photoelectric equation.

Answer the following question.
Define the term "Threshold frequency", in the context of photoelectric emission.

Why it is the frequency and not the intensity of the light source that determines whether the emission of photoelectrons will occur or not? Explain.

Which one of the following metals does not exhibit emission of electrons from its surface when irradiated by visible light?

Read the following paragraph and answer the questions.

1. Which light beam has the highest frequency and why?
2. Which light beam has the longest wavelength and why?
3. Which light beam ejects photoelectrons with maximum momentum and why?

How will the de-Broglie wavelength associated with an electron be affected when the velocity of the electron decreases? Justify your answer.

How would the stopping potential for a given photosensitive surface change if the intensity of incident radiation was decreased? Justify your answer.

How would the stopping potential for a given photosensitive surface change if the frequency of the incident radiation were increased? Justify your answer.

How will the de-Broglie wavelength associated with an electron be affected when the accelerating potential is increased? Justify your answer.

What is the effect of threshold frequency and stopping potential on increasing the frequency of the incident beam of light? Justify your answer.

Show that the radius of the orbit in hydrogen atom varies as n², where n is the principal quantum number of the atom.

Using Rutherford's model of the atom, derive the expression for the total energy of the electron in hydrogen atom. What is the significance of total negative energy possessed by the electron?

Using Bohr's postulates of the atomic model, derive the expression for radius of n^th electron orbit. Hence obtain the expression for Bohr's radius.