Question

An object 10cm high is placed 30cm from a diverging lens of focal length 60cm. Determine the nature and size of the image.

Answer 1

image is virtual, erect, is 20 cm away, and is diminished

Explanation:

height of object,h=10cm

distance of object, u= -30 cm

focal length, f = -60 cm ... since it is concave lens(diverging lens), the focal length will be negative

therefore, v=? and h'=?

therefore, by the lens formula,

1 = 1 - 1

f v u

therefore,

-1 = 1 + 1

60 v 30

therefore,

1 = -1 - 1

v 60 30

therefore,

1 = -1-2

v 60

therefore, v= 60 = -20

-3

therefore, v= -20

therefore, the image is virtual and erect since v is negative and is 20 cm away

m= v = -20 = 2 ... (1)

u -30 3

therefore, m=h' ...(2)

h

therefore, from (1) & (2),

2 = h'

3 10

therefore, h'= 20 =6.7

3

therefore, the height of the image is 6.7cm

therefore, m= v = 2 = 0.67

u 3

therefore, the image is diminished since m=0.67

Hope it helps!!