Question

A 5.0 cm tall object is placed perpendicular to the

principal axis of a convex lens of focal length 20 cm.

The distance of the object from the lens is 30 cm. By

calculation determine (i) the position and (ii) the size

of the image formed.​

Answer 1

Explanation:

Answer: The size of the image is 10 cm and the image is real and inverted.

Explanation:

Given that,

Height of object h = 5 cm

Focal length f = 20 cm

The distance of the object u = -30 cm

Using lens's formula

\dfrac{1}{f}=\dfrac{1}{v}-\dfrac{1}{u}

f

1

=

v

1

−

u

1

\dfrac{1}{20}=\dfrac{1}{v}-\dfrac{1}{-30}

20

1

=

v

1

−

−30

1

\dfrac{1}{v}=\dfrac{1}{60}

v

1

=

60

1

v = 60v=60

The image is formed at 60 cm on the other side from the lens.

The magnification is

m = \dfrac{v}{u}m=

u

v

m = \dfrac{60}{-30}m=

−30

60

m = -2m=−2

The image is real, inverted .

Size of the image,

m = \dfrac{h'}{h}m=

h

h

′

-2 = \dfrac{h'}{5}−2=

5

h

′

h' = -10 cmh

′

=−10cm

Hence, The size of the image is 10 cm and the image is real and inverted.

Answer 2

Answer:

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