Question

Suppose a concave neniscus lens is made firom glass with n = 1.50, with a focal length of 50.0cm and the radius of curvature of the concave surface is 30.0cm. 

i. What is the radius of curvature of the convex surface? Is this a diverging lens or a converging lens? (2 marks)

ii. If I were to use the same lens to magnify a small insect using the same focal length to form a Virtual image, that is, 45.0cm in front of the lens; where should the small insect be

placed? (2 marks)

Answer 1

1)

$\frac 1F=(n-1)(\frac 1{R_1}-\frac 1{R_2}),\implies$

$R_1=\frac{(n-1)R_2F}{R_2+F}=9.375~cm,$

$R_1<R_2,$ converging lens,

2)

$\frac 1f+\frac 1d=\frac 1F,$

$d=\frac{fF}{f-F}=450~cm.$