Important Questions
1. Define a wavefront. Using ‘Huygens’ principle, draw the shape of a refracted wavefront, when a plane wavefront is incident on a convex lens.
2. Use Huygen’s principle to verify the laws of refraction.
3. Use huygen’s principle to explain the formation of diffraction pattern due to a single slit illuminated by a monochromatic source of light. When the width of the slit is made double the original width, how would this affect the size and intensity of the central diffraction band?
4. (a) Define wave front. Use Huygens’ principle to verify the laws of refraction.
(b) How is linearly polarised light obtained by the process of scattering of light? Find the Brewster angle for air – glass interface, when the refractive index of glass = 1.5
5. Describe Young’s double slit experiment to produce interference pattern due to a monochromatic source of light. Deduce the expression for the fringe width.
Sample Questions
1. (a) Why are coherent sources necessary to produce a sustained interference pattern?
(b) In Young’s double slit experiment using monochromatic light wavelength ‘λ’, the intensity of light at a point on the screen where the path differences is ‘λ’, is K units.
Find out the intensity of light at a point where path difference is λ/3 .
2. Answer the following questions:
(a) In a double slit experiment using light of wavelength 600 nm, the angular width of the fringe formed on a distant screen is 0.1°.
Find the spacing between the two slits.
(b) Light of wavelength 5000 Å propagating in air gets partly reflected from the surface of water. How will the wavelengths and frequencies of the reflected and refracted light be affected?
3. In Young’s double slit experiment, the two slits are separated by a distance of 1.5 mm and the screen is placed 1 m away from the plane of the slits. A beam of light consisting of two wavelengths 650 nm and 520 nm is used to obtain interference fringes. Find :
(a) the distance of the third bright fringe for λ = 520 nm on the screen from the central maximum.
(b) the least distance from the central maximum where the bright fringes due to both the wavelengths coincide.
4. In a single slit diffraction experiment, when tiny circular obstacle is placed in path of light from a distance source, a bright spot is seen at the centre of the shadow of the obstacle. Explain why? State two points of difference between the interference patterns obtained in Young’s double slit experiment and the diffraction pattern due to a single slit.
5. (a) In Young’s double slit experiment, describe briefly how bright and dark fringes are obtained on the screen kept in front of a double slit. Hence obtain the expression for the fringe width.
(b) The ratio of the intensities at minima to the maxima in the Young’s double slit experiment is 9 : 25. Find the ratio of the widths of the two slits.
6. If the angle between the pass axis of polarizer and the analyser is 45°, write the ratio of the intensities of original light and the transmitted light after passing through the analyzer.
7. (a) When a wave is propagating from a rarer to a denser medium, which characteristic of the wave does not change and why ?
(b) What is the ratio of the velocity of the wave in the two media of refractive indices μ1 and μ2?
