Question

find the focal length of convexo concave lens if refractive index is n​

Answer 1

ANSWER

From LMF,

f

1

=(n−1)(

R

1

1

−

R

2

1

)

Since it is diverging , f=−24cm

Given that R

1

=2R

2

,n=1.5

−24

1

=(1.5−1)(

2R

2

1

−

R

2

1

)

−12

1

=

2R

2

−1

R

2

=6cm,R

1

=12cm

Answer 2

Answer is 12.5 cm.............