Question

A convex lens produces a 1.8-cm-tall real image that is 10.4 cm from the lens and inverted. If the focal length of the lens is 6.8 cm, what are the object position and height?

A) Object position: 17.2 cm, Object height: 1.8 cm
B) Object position: 3.6 cm, Object height: 1.8 cm
C) Object position: 3.6 cm, Object height: 3.6 cm
D) Object position: 17.2 cm, Object height: 3.6 cm

Answer 1

Object position is 19.6 cm, and Object height is 3.4 cm (Option D).

How to calculate the object's position?

The position of the object is calculated by applying the formula for lens as shown below;

1/f = 1/v + 1/u

where;

• f is the focal length of the lens
• u is the object distance
• v is the image distance

1/6.8 = 1/10.4 + 1/u

1/u = 1/6.8 - 1/10.4

1/u = 0.0509

u = 1/(0.0509)

u = 19.6 cm

The magnification of the image is;

M = v/u = Hi/H

10.4/19.6 = 1.8 / H

H = 3.4 cm