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Limit of Resolution

A small teles...

Question

A small telescope has an objective lens of focal length $150 c m$ and eyepiece of focal length $5 c m$ . What is the magnifying power of the telescope for viewing distant objects in normal adjustment?
If this telescope is used to view a $100 m$ tall tower $3$ km away, what is the height of the image of the tower formed by the objective lens?

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Solution

Given, Focal length of objective, $f_{o} = 150 c m$

Focal length of eye-piece, $f_{e} = 5 c m$

Height of tower, $H = 100 m$

Distance of tower, $u = 3 k m$

Magnification of telescope is given by:

$m = - \frac{f_{o}}{f_{e}} (1 + \frac{f_{e}}{D})$

$m = - \frac{150}{5} (1 + \frac{5}{25}) = - 36$

Also, $m = \frac{t a n β}{t a n α}$

$t a n α = H / u = 100 / 3000 = 1 / 30$

$t a n β = - \frac{36}{30}$

$t a n β = \frac{H^{'}}{D}$

Height of the image of the tower, $H^{'} = - \frac{- 36 \times 25}{30} = - 30 c m$

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(a) For the telescope described in Exercise (a)[A small telescope has an objective lens of focal length

140 c m

and an eyepiece of focal length

5.0 c m

. What is the magnifying power of the telescope for viewing distant objects when

(a) the telescope is in normal adjustment (i.e., when the final image is at infinity)?],

What is the separation between the objective lens and the eyepiece?

(b) If this telescope is used to view a

100 m

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(c) What is the height of the final image of the tower if it is formed at

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Q. Define magnifying power of a telescope. Write its expression.
A small telescope has an objective lens of focal length

150 c m

and an eye piece of focal length

5 c m

. If this telescope is used to view a

100 m

3 k m

away, find the height of the final image when it is formed

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away from the eye piece.

Q. A) A small telescope has an objective lens of focal length

140 cm

and an eyepiece of focal length

5.0 cm

. What is the magnifying power of the telescope for viewing distant objects when the telescope is in normal adjustment (i.e. when the final image is at infinity)?

B) A small telescope has an objective lens of focal length

140 cm

and an eyepiece of focal length

5.0 cm

. What is the magnifying power of the telescope for viewing distant objects when the final image is formed at the least distance of distinct vision

(25 cm)

?

Q. A) A small telescope has an objective lens of focal length

140 cm

and an eyepiece of focal length

5.0 cm

. What is the separation between the objective lens and the eyepiece?

B) A small telescope has an objective lens of focal length

140 cm

andan eyepiece of focal length

5.0 cm

. If this telescope is used to view a

100 m

3 km

away, what is the height of the image of the tower formed by the objective lens?

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140 cm

and an eyepiece of focal length

5.0 cm

. What is the height of the final image of the tower if it is formed at

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\frac{140}{30} cm)

Q. The small telescope has a focal length of

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and an eyepiece of focal length 5 cm. it is used to view a

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away. What is the height of the image of the tower formed by the objective?

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