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Concepts Of Physics MCQ Edition [Volume 1]

Exam: Concepts Of Physics MCQ Edition [Volume 1]
Subject: Physics
Chapter: Optical Instruments

Concepts Of Physics MCQ Edition [Volume 1] · Physics · Optical Instruments

An astronomical telescope's eyepiece has a focal length of 10 cm ....

An astronomical telescope's eyepiece has a focal length of

10 \text{ cm}

. When the telescope is focussed for normal vision of distant objects, the tube length is

1.0 \text{ m}

. Determine the focal length of the objective and the magnifying power of the telescope.

Options

A $100 \text{ cm}$ , $10$
B $90 \text{ cm}$ , $9$
C $110 \text{ cm}$ , $11$
D $90 \text{ cm}$ , $10$

Correct answer

B. $90 \text{ cm}$ , $9$

Step-by-step solution

For normal vision, the final image is formed at infinity. The tube length of the telescope is given by

L = f_o + f_e

.

Given

L = 1.0 \text{ m} = 100 \text{ cm}

and

f_e = 10 \text{ cm}

.

100 = f_o + 10

f_o = 90 \text{ cm}

The magnifying power of the telescope for normal vision is given by

M = \dfrac{f_o}{f_e}

.

M = \dfrac{90}{10} = 9

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