Question

3. An object of 7cm high
is placed at 27cm in front
of a concave mirror of
focal length 18cm, At
what distance from the
mirror should a screen be
placed so that a sharp
focussed image can be
obtained. Calculate the
size and nature of the
image.​

Answer 1

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Explanation:

Given that

u = – 27 cm

f = – 18 cm

h0 = 7.0 cm

Find out

We need to find out size and nature of image

Formula

We know the mirror formula that

1/v = 1/f- 1/u

1/v = -1/18 + 1/27 = -1/54

V = – 54 cm

The screen must be placed at a distance of 54 cm from the mirror in front of it.

hi/h0= v/u

hi/h0= v/u

hi/7 = +54/-27 hi= -2 x 7 = -14 cm.

Thus, the image is of 14 cm length and is inverted image

Answer 2

Given that

u = – 27 cm

f = – 18 cm

h0 = 7.0 cm

Find out

We need to find out size and nature of image

Formula

We know the mirror formula that

1/v = 1/f- 1/u

1/v = -1/18 + 1/27 = -1/54

V = – 54 cm

The screen must be placed at a distance of 54 cm from the mirror in front of it.

h1/h0= v/u

h1/h0= v/u

h1/7 = +54/-27 hi= -2 x 7 = -14 cm.

Thus, the image is of 14 cm length and is inverted image