Question

A converging lens has a focal length of 10.0 cm . For each of two objects located to the left of the lens, one at a distance of s1 = 20.5 cm and the other at a distance of s2 = 5.00 cm , determine the following.

Determine the image position.Express your answer in centimeters separated by a comma to three significant figures.

is the image real or virtual

Answer 1

i)
Consider the case of s1
Object distance, u = 20.5 cm
Focal length, f = 10 cm
Consider v as the image distance.

Using the formula, 1/f = 1/u + 1/v.
1/v = 1/f - 1/u
= 1/10 - 1/20.5
= 0.051
v = 1/0.051
= 19.5 cm, the image is real

ii)

Consider the case of s2
Object distance, u = 5 cm
Focal length, f = 10 cm
Consider v as the image distance.

Using the formula, 1/f = 1/u + 1/v.
1/v = 1/f - 1/u
= 1/10 - 1/5
= - 0.1
v = -1/0.1
= -10.0 cm, the negative sign shows that the image is virtual