Question

When an object is placed 20cm from a concave mirror,a real image magnified three times is formed . Find the focal length of the mirror.Where must the ovject be placed to give a virtual image three times the hight of the object?​

Answer 1

When an object is placed 20cm from a concave mirror,a real image magnified three times is formed . Find the focal length of the mirror.Where must the ovject be placed to give a virtual image three times the hight of the object?​

Answer

Given

Magnification m = -3

U = - 20 cm

V = ?

m = -v/u

-3 = -v/(-20)

By calculating we will get the answer as

V = - 60 cm

So that the image is located 60 cm Infront of the mirror

☣ MIRROR FORMULA ☣

1/v + 1/u = 1/f

1/(-60) + 1/(-20) = 1/f

By calculating we will get the answer as

f = -15cm

(b). m = h2 /h1

m = -v/u =3

V = -3 u

Applying

☣ MIRROR FORMULA ☣

1/(-3u) +1/u =1/(-15)

By calculating you will get the answer as

☣ U = -10 cm ☣

Answer 2

Answer:

Thus, the focal length of the concave mirror is 15 cm. (b) Now, if the image is virtual and 3 times magnified, then we have to find the position of the object.

Thus, the object should be placed at a distance of 10 cm to get a virtual image three times the height of the object.