Question

A 10 cm tall object is placed perpendicular to the principal axis of a convex lens of focal length 30 cm. The distance of the object from the lens is 20 cm. Find the:
(a)Position
(b)Nature
(c)Size of the image formed.​

Answer 1

Solution

Given :-

• f = 30cm
• u = -20 cm
• v = ?

Find :-

• position of image
• Nature of image
• Size of the image formed.

Explanation

Using Lens Formula

★ 1/f = 1/v - 1/u

Keep value of f & u

==> 1/30 = 1/v - 1/(-20)

==> 1/v = 1/30 - 1/20

==> 1/v = (2 - 3)/60

==> 1/v = -1/60

==> v = -60 cm

Since,

• image is at the distance of 60 cm from the lens .
• Negative sign indicate image will be same side on lens as the object and image be real .

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Now, Calculate size of image

Using Magnification Formula

★ m = h"/h' = v/u

==> h"/ 10 = -60/(-20)

==> h" = 3 × 10

==> h" = 30 cm

Hence

• position of image is 60 cm on same side of lens and image is 30 cm , its is erect image

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