Geometric & Wave Optics
posted by Matrix School 1 on .
An astronomical telescope consists an objective of focal lenght 100cm and an eyepiece of focal lenght 8cm.
calculate the angular magnification of the telescope and also determine the distance between the two lenses.

For astronomical telescopes, the objects are at infinity, so parallel rays reach the objective. The eyepiece is therefore placed at a distance from the objective equal to the focal length. At this location, the magnification is equal to the quotient of the focal lengths.
Magnification
= 100 cm / 8 cm
= 12.5 times.
Note: eyepieces usually have focal lengths in the millimetres range, so it is likely that the focal length of the eyepiece is 8 mm., in which case
Magnification
= 100 cm /8 mm
= 125 times. 
1. An object,30mm high ,is 90mm from a convex lens. The focal length is 60mm det the positive height an nature of the image. Draw an accurate diagram for the formation of the image. 2.calculate its magnification?