Question

A concave lens is a focal length of 30 cm. Find the position and magnification (m) of image for an object placed in front of it at distance 30 cm. State whether the image is real on virtual?

Answer 1

Given,
Object distance, u = -30 cm
Focal length, f = -30 cm
Image distance, v = ?
Len’s formula is
1 / f = 1 / v – 1 / u
1 / -30 = 1 / v – 1 / -30
1 / v = -1 / 30 – 1 / 30
1 / v = -2 / 30
1 / v = – 1 / 15
v = -15
The relation between u and v is
m = v / u
m = -15 / -30
m = 0.5
∴ The image formed is virtual and erect.