CBSE Class 12 · 2018 · Geometrical OpticsLong Answer

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(a) Draw a ray diagram to show image formation when the concave mirror produces a real, inverted and magnified image of the object.
(b) Obtain the mirror formula and write the expression for the linear magnification.
(c) Explain two advantages of a reflecting telescope over a refracting telescope.

Solution

(a) For an object between

F

and

C

of a concave mirror, the image is real, inverted and magnified (beyond

C

).
(b) From similar triangles (

△ A^{'} B^{'} F \sim △ M P F

and

△ A B P \sim △ A^{'} B^{'} P

) and the sign convention:

\frac{1}{v} + \frac{1}{u} = \frac{1}{f}, m = \frac{h ^{'}}{h} = - \frac{v}{u}

(c) Advantages of a reflecting telescope: (1) \emph{no chromatic aberration} (mirror objective); (2) a large-aperture parabolic mirror gives \emph{high resolving power and a bright image} and is free from spherical aberration.

CBSE Class 12 Board · 2018 · Subjective

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CBSE Class 12 · 2018 · Geometrical OpticsLong Answer

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