Question

An object of 3 cm in size is placed at s distance of 10 cm from a concave mirror
of focal length 20 cm. At what distance from the mirror should a screen be
placed to get the sharp image? Find the size and nature of the image.

Answer 1

Answer:

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

Answer:

Given: h

1

=3cm, u=−10cm, f=−20cm

We know that

v

1

+

u

1

=

f

1

⇒

v

1

=

f

1

−

u

1

=

(−20)

1

−

(−10)

1

=−

20

1

+

10

1

=

20

−1+2

=

20

1

∴v=20cm

The image is formed at a distance of 20cm behind the mirror,

And

m=−

u

v

=

h

1

h

2

⇒

(−10)

(20)

=

3

h

2

⇒h

2

=6cm

Image is 6 cm in size, virtual and erect.

Explanation:

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