A Galilean telescope has an objective of focal length 100 cm and magnifying power 50. The distance between the two lenses in normal adjustment will be:

Question

A Galilean telescope has an objective of focal length 100 cm and magnifying power 50. The distance between the two lenses in normal adjustment will be: (A) 98 cm (B) 100 cm (C) 150 cm (D) 200 cm

Tardigrade Admin · Accepted Answer

In Galilean telescope a convergent lens is used as the objective and a divergent lens as the eye piece. Magnifying power and length of telescope are written as:

M = \frac{f _{o}}{u _{e}}

and

L = f_{o} - u_{e}

In normal adjustment, i.e., in relaxed eye state

u_{e} = f_{e}

So,

M_{\infty} = \frac{f _{o}}{f _{e}} = 50

or

f_{e} = \frac{f _{o}}{50} = \frac{100}{50} = 2 c m

and

L_{\infty} = f_{o} - f_{e}

∴

L_{\infty} = 100 - 2 = 98 c m

Q. A Galilean telescope has an objective of focal length 100 cm and magnifying power 50. The distance between the two lenses in normal adjustment will be:

98 cm

100 cm

150 cm

200 cm

Q. A Galilean telescope has an objective of focal length $100$ cm and magnifying power $50$ . The distance between the two lenses in normal adjustment will be: