Question

A giant refracting telescope at an observatory has an objective lens of focal length 15m. If an eyepiece of focal length 1.0 cm is used, what is the angular magnification of the telescope?

Answer 1

Hint: We are given a refracting telescope having objective focal length 15 m and eyepiece of focal length 1 cm = 0.01m. To find out the angular magnification we can use the magnification formula which is focal length of objective divided by focal length of eyepiece to find out.

Complete step by step answer:
Angular magnification of the telescope is given by the formula,
$m=\dfrac{{{f}_{0}}}{{{f}_{e}}} \\$
where,
$f_o$ = Focal length of the objective = 15cm
$f_e$= Focal length of the eyepiece = 1cm
$m$= magnification = ?
$m =\dfrac{15}{0.01} \\$
$\therefore m =1500 \\ $

So, the value of angular magnification comes out to be 1500.

Additional Information:
When light moves from one medium to another then it either bends towards the normal or away from the normal. It is called the refraction of the light. The lens is used for refraction in this case. A simple refracting telescope consists of two lenses, the objective and the eyepiece, the objective lens produces an image of a faraway object at its focus and the eyepiece lens makes it bigger. There is another type of telescope which is used and called reflecting telescope. The advantage of using a reflecting telescope is that it is free from achromatic aberration. This defect occurs due to the use of lenses and refraction of light.

Note:
Angular magnification is a dimensionless number as it is the ratio of two lengths.
A refracting telescope uses a combination of lenses to produce an image of a distant object.
Refraction of light is used to form the image in this case.