Question

what is the focal length of double concave lens kept in air with two spherical surface of radius 30 and radius 60 CM take refractive index of lines as n=1.5​

Answer 1

Explanation:

Using lens makers formula

f

1

=(μ−1)[

R

1

1

−

R

2

1

] where R

1

=−ve

f

1

=(1.5−1)[

(−30)

1

−

60

1

]

f

1

=(0.5)[

60

3

]=−0.5×

20

1

f=−40cm