Question

What is the distance of an object from a concave
mirror of focal length 15c
m so that the size of the
real image is three times the size of the object?​

Answer 1

Given:-

• Focal length ,f = -15cm

• Size of image is three times the size of the object.

To Find:-

• Object distance ,u

Solution:-

Type of mirror concave mirror.

Image formed is real .

According to given Question

As we know that

•magnification ,m = -v/u

→ -3 = -v/u

→ -v = -3u

→ v = 3u

here the image formed is 3 time larger than the object .

Now using mirror formula

• 1/v +1/u = 1/f

Substitute the value we get

→ 1/v + 1/3u = 1/(-15)

→ 1/u +1/3u = -1/15

→ 3+1/3u = -1/15

→ 4/3u = -1/15

→ u = -1×3/15×4

→ u = -5×4

→ u = -20cm

∴ The object distance is 20cm in front of the mirror.

v= 3u

→ v = 3×(-20)

→ v = -60 cm

∴ The image distance is 60 cm in front of the mirror.