Question

A concave mirror of focal length 15 cm is kept in front of an object at a
distance of 45 cm from it. If the object is 1.0 cm high, what will be the
size of the image?

Answer 1

Answer:

1/2 cm or 5 mm

Explanation:

f = - 15 cm

u = - 45 cm

v = ?

1/f = 1/v + 1/u

1/-15 = 1/v + 1/-45.

1/v = -1/15 - (-1/45)

= -1/15 + 1/45

= (-3 + 1) / 45

1/v = -2/45 .

Therefore,

v = -45/2.

m = -v/u.

= -(-45/2) ÷ -45.

= (45/2) × -1/45.

= -1/2.

We also know that,

m = height of image ÷ height of object.

That is,

-1/2 = height of image ÷ 1.

Height of image = -1/2 × 1 = -1/2 cm

= -5 mm.

Original height of image is 5mm or 1/2cm.

Negative sign in front of the image height indicates that, IMAGE IS INVERTED.

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