Question

a convex lens forms a real image 4 times magnified at the distance of 60 cm from the lens calculate the focal length and the power of the lens

Answer 1

m = -4
v÷u =-4
60÷u =-4
u =-15 cm

1÷v- 1÷u =1 ÷f
1÷60 - 1÷-15 =1÷f
1÷60+1÷15 =1÷f
(1+4)÷60 =1÷f
5÷60 = 1 ÷ f
f=12cm

f=0.12m
p = 1÷f D
p =1 ÷ 0.12
p= 8.33D


p=8.33D. f =12 cm

Answer 2

Answer:

Explanation:

Convex lens

m= -4 ( image is real )

v= 60 cm

m

u

v = =− 4 u

v

4 & = − 4

60 =−

=− 15 cm

From the lens formula,

f

1

v u

1 1 = − 60

1

15

1 = − −

60

1 4 = +

60

5 = 12

1 =

Focal length, f = 12 cm 100

12 = m

The power of the lens, P f in m

1 = ^ h

m

1

100

= 12 D 12

100 =

= 8 33 . D