(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.

State three characteristic which distinguish interference pattern due to two cohrently illuminated sources as compard to that observed in a diffraction pattern due to 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.

In a singleslit diffraction experiment, when a tiny circular obstacle is placed in the path of light from a distant source, a bright spot is seen at the centre of the shadow of the obstacle. Explain why ? State two points of difference the interference pattern obtained in Young's double slit experiment and the diffraction pattern due to a single slit.

(a) Define a wavefront. Using Huygen's principle, verify the laws of reflection at a plane surface . (b) In a single slit diffraction experiment the wildth of the slit is made double the orignal width. How does this affect the size and intensity of the central diffraction band ? Explain. (c) When a tiny circular obstacle in placed in the path of light from a distance source, a bright spot is seen at the centre of the obstacle . Explain why.

Answer the following: (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) 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.