Question

what is the focal length of double concave lens kept in air with two sphere surface of radii R1=30cm R2=60cm?take refractive index of lens n=1.5

Answer 1

Answer:

r565 r32 cbccn

Explanation:

the gocal length is concave

Answer 2

Answer:

By lens makers formula

$\frac{1}{f} =(\frac{n2}{n1} -1)(\frac{1}{R1} -\frac{1}{R2} )\\\frac{1}{f} =(\frac{1.5}{1} -1)(\frac{1}{30} -(\frac{-1}{60}) )\\\frac{1}{f}=(\frac{1}{2})(\frac{1}{20})\\f=40cm$