Ray Optics and Optical Instruments

How does the frequency of a beam of ultraviolet
light change when it goes from air into glass ?
[Delhi 2001]

What is the focal length of a plane mirror ?
[Delhi 2001C]

When light undergoes refraction, what happens
to its frequency ? [AI 2000C]

When light undergoes refraction at the surface
of separation of two media, what happens to
its wavelength ? [AI 2000C]

The image of an object formed by a lens on the
screen is not in sharp focus. Suggest a method
to get clear focussing of the image on the screen
without disturbing the position of the object,
the lens or the screen. [Delhi 1998]

When a ray of light is passed through a prism,
under what condition will the angle of incidence
be equal to the angle of emergence ?
[AI 2004C]