(a) Define a wavefront. Use Huygen' principle to shown diagrammatically the propagation of a plane wavefront from the intant `t_(1)=0` to later time `t_(2)`.
(b) State briefly two features which can distinguish the characteristic features of an interference pattern from those observed in the diffraction pattern due a single slit.

(a) Using Huygen's principle draw a diagram to whow propagation of a front originating from a monochrmatic source. (b) Desctibe diffraction of light due to a single slit. Explain formation of a pattern of fringes obtained on the screen and plot showing variation of intensity with angle theta in single slit diffraction.

(a) What is a wave front? How does it propagate? Using Huygens' principle, explain reflection of a plane wavefront from a surface and verify the laws of reflection. (b) A parallel beam of light of wavelength 500 nm falls on a narrow slit and the resulting diffraction pattern is obtained on a screen 1 m away. If the first minimum is formed at a distance of 2.5 mm from the centre of screen, find the (i) width of the slit, and (ii) distance of first secondary maximum from the centre of the screen.

(a) Derive the relation a sin theta=lambda for the first minimum of the diffraction pattern produced due to a single slit of width ‘a’ using light of wavelength lambda . (b) State with reason, how the linear width of 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. (c) Using the monochromatic light of same wavelength in the experimental set-up of the diffraction pattern as well as in the interference pattern where the slit separation is 1 mm, 10 interference fringes are found to be within the central maximum of the diffraction pattern. Determine the width of the single slit, if the screen is kept at the same distance from the slit in the two cases.

(a) In what way is diffraction from each slit related to the interference pattern in a double slit experiment ? (b) Two wavelengths of sodium light 590 nm and 596 nm are used, in turn, to study the diffraction taking place at a single slit of aperture 2 xx 10^(-4)m. The distance between the slit and the screen is 1.5 m. Calculate the separation between the positions of the first maxima of the diffraction pattern obtained in the two cases.

(a) Write two characteristics features distinguishing the diffraction pattern from the interference fringes obtained in Young's double slit experiment. (b) Two wavelengths of sodium light 590 nm and 596 nm are used , in turn, to study the diffraction taking place due to a single slit of aperture 1xx10^(-4)m . The distance between the slit and the screen is 1.8m. Calculate the separation between the positions of the first maxima of the diffraction pattern obtained in the two cases.