Question

Answer these questions

1) would there be any change in focal length of mirror if it is dipped in water

2) why mirror used in search lights are parabolic

Answer 1

Answer ;-1 } focal length of mirrors does not depend on the external medium in which it is held. so there will be no change in focal length.

Answer;-2} in a parabolic mirrors,, when source is at the focus , beam of light produced over the entire cross-section of the mirror is a parallel beam.

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Answer 2

Answer:

1.The focal length of the concave mirror does not change when it is immersed in water because focal length of a mirror does not depend upon the refractive index of the medium. ... Therefore, when a convex lens is dipped into water, its focal length increases.

2.Due to large aperture of mirror , marginal rays give a divergent beam . But in case of parabolic mirror , when source is at the focus , beam of light produced over the entire cross-section of the mirror is a parallel beam.