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

**(b)** If this
telescope is used to view the moon, what is the diameter of the image
of the moon formed by the objective lens? The diameter of the moon is
3.48 × 10 ^{ 6 }
m, and the radius of lunar orbit is 3.8 × 10 ^{ 8 }
m.

Focal
length of the objective lens, *f*_{o}
= 15 m = 15 ×
10^{2} cm

Focal
length of the eyepiece, *f*_{e}
= 1.0 cm

**(a)** The
angular magnification of a telescope is given as:

Hence, the angular magnification of the given refracting telescope is 1500.

**(b) **Diameter
of the moon,* d*
= 3.48 ×
10^{6} m

Radius
of the lunar orbit, *r*_{0}
= 3.8 ×
10^{8} m

Let be the diameter of the image of the moon formed by the objective lens.

The angle subtended by the diameter of the moon is equal to the angle subtended by the image.

Hence, the diameter of the moon’s image formed by the objective lens is 13.74 cm

**
**