Science (English Medium) Class 12 - CBSE Important Questions for Physics

When monochromatic light is incident on a surface separating two media, why does the refracted light have the same frequency as that of the incident light?

 What is the effect on the interference fringes to a Young’s double slit experiment when

(i) the separation between the two slits is decreased?

(ii) the width of a source slit is increased?

(iii) the monochromatic source is replaced by a source of white light?

Justify your answer in each case.

The intensity at the central maxima in Young’s double slit experimental set-up is I₀. Show that the intensity at a point where the path difference is λ/3 is I₀/4.

Obtain the conditions for the bright and dark fringes in diffraction pattern due to a single narrow slit illuminated by a monochromatic source.

Explain clearly why the secondary maxima go on becoming weaker with increasing.

When the width of the slit is made double, how would this affect the size and intensity of the central diffraction band? Justify.

State with reason, how the linear width of the central maximum will be affected if
(i) monochromatic yellow  light is replaced with red light, and
(ii) distance between the slit and the screen is increased.

Answer the following question.
Describe any two characteristic features which distinguish between interference and diffraction phenomena. Derive the expression for the intensity at a point of the interference pattern in Young's double-slit experiment.

Answer the following question.
In the diffraction due to a single slit experiment, the aperture of the slit is 3 mm. If monochromatic light of wavelength 620 nm is incident normally on the slit, calculate the separation between the first order minima and the 3rd order maxima on one side of the screen. The distance between the slit and the screen is 1.5 m.

Write the conditions on path difference under which constructive interference occurs in Young’s double-slit experiment.

In a single slit diffraction experiment, the width of the slit is increased. How will the

1. size and
2. intensity

of central bright band be affected? Justify your answer.

A plane wave front AB propagating from denser medium (1) into a rarer medium (2) is incident on the surface P₁P₂ separating the two media as shown in fig.

Using Huygen’s principle, draw the secondary wavelets and obtain the refracted wave front in the diagram.

Write two points of difference between an interference pattern and a diffraction pattern.

How can you differentiate whether a pattern is produced by a single slit or double slit?

Derive the expression for the angular position of (i) bright and (ii) dark fringes produced in a single slit diffraction.

In Young's double slit experiment using light of wavelength 600 nm, the slit separation is 0.8 mm and the screen is kept 1.6 m from the plane of the slits. Calculate

1. the fringe width
2. the distance of (a) third minimum and (b) fifth maximum, from the central maximum.

State two conditions for two light sources to be coherent.

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.