The focal length of a thin convex lens for red and blue colours is 100.5 cm and 99.5 cm .The dispersive power of the lens is

Options

A. 0.01
B. 0.02
C. 1.005
D. 0.995

Answer

A

Explanation

(a) We have, `f_(y)=sqrt(f_(R)f_(b))`
`f_(y)=sqrt(100.5xx99.5)=99.99`
Also, omega=`(f_(R)-f_(b))/(f_(y))=(100.5-99.5)/99.99`
Dispersive power,omega=`1/99.99=0.01`