8. A piece of copper and other of germanium are cooled from the room temperature to 80 K, then ?

7. Diamond is very hard because ?

24. A parallel beam of monochromatic light of wavelength 5000Å is incident normally on a single narrow slit of width 0.001 mm. The light is focussed by a convex lens on a screen placed in focal plane. The first minimum will be formed for the angle of diffraction equal to ?

4. Interference was observed in interference chamber where air was present, now the chamber is evacuated, and if the same light is used, a careful observer will see ?

10. Time taken by sunlight to pass through a window of thickness 4 mm whose refractive index is 3/2 is ?