Question

PLZ HELP ME OUT

A 2 cm high object is placed 12 cm from a convex lens, perpendicular to the principal axis.The lens forms a real image,whose size is 1.5 cm.Find the power of lens?

Answer 1

height of object= 2cm
height of image= -1.5cm ( Since image is real and inverted )
u = -12cm
v= ?

We know,
m= height of image/height of object = v/u
m= -1.5/2 = v/-12
v= 18/2 = 9cm

From lens formula,
1/f= 1/v - 1/u
1/f= 1/9 - (-1/12)
= 1×4/9×4 + 1×3/12×3
= 7/36cm
f= 36/7cm
f = 36/700m

Also,

P= 1/f = 700/36 = 19.44D

Answer 2

Answer:

Explanation:

height of object= 2cm

height of image= -1.5cm ( Since image is real and inverted )

u = -12cm

v= ?

We know,

m= height of image/height of object = v/u

m= -1.5/2 = v/-12

v= 18/2 = 9cm

From lens formula,

1/f= 1/v - 1/u

1/f= 1/9 - (-1/12)

= 1×4/9×4 + 1×3/12×3

= 7/36cm

f= 36/7cm

f = 36/700m

Also,

P= 1/f = 700/36 = 19.44D