The distance between the objective lens and the eye lens of an astronomical telescope when adjusted for parallel light is 100 cm. The measured value of the magnification is 19. The focal lengths of the lenses are :

Options

A. 85 and 15 cm
B. 82 and 18 cm
C. 95 and 5 cm
D. 50 and 50 cm

Answer

C

Explanation

` f _ 0 + f _e = 100 & ( f _ 0 ) /( f _ e ) = 19 `
` therefore 20 f _ e = 100 rArr f _ e = 5 cm `
` f _ 0 = 95 cm `