Question

For an astronomical telescope having objective lens of focal length 10 m and eyepiece lens of focal length 10 cm, telescope’s the tube length and magnification respectively are __________.
.Fill in the blank with the correct answer from the options given below.

• A. 20 cm, 1
• B. 1000 cm, 1
• C. 1010 cm, 1
• D. 1010 cm, 100

Answer 1

Answer: (D)

1010 cm, 100

Answer 2

The tube length of an astronomical telescope is the sum of the focal lengths of the objective and the eyepiece:
L = f(objective) + f(eyepiece) = 10m + 0.1m = 1010 cm.
The magnification is given by:
$M = \frac{fobjective}{feyepiece} = 10 0.1 = 100.$