Question

an object of 3 cm high is placed at a distance of 8 cm from a concave mirror which produces a virtual image four centimetres high . what is the focal length of mirror​

Answer 1

Given:-

• Object height ,hi = 3cm

• Object distance , u= -8cm

• Image height ,ho = 4cm

To Calculate :-

• Focal length of mirror (f).

Solution:-

As we know that

Magnification ,m = hi/ho = -v/u

Substitute the value we get

→ 3/4 = -v/(-8)

→ 3/4 = v/8

→ v = 3×8/4

→ v = 24/4

→ v = 6 cm

Now using Mirror Formula

→ 1/v +1/u = 1/f

Substitute the value we get

→ 1/6 + 1(-8) = 1/f

→ 1/6 - 1/8 = 1/f

→ 4-3/24 = 1/f

→ 1/24 = 1/f

→ 1/f = 1/24

→ f = 24cm

∴. The Focal length of the mirror is 24cm.

Answer 2

Answer:

24 cm

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