Size of image of an object by a mirror having a focal length of 20cm is observed to be reduced to 1:3rd of its size? At what distance the object has been placed from the mirror. What is nature of image and mirror?

Open in App

Solution

Focal length of the mirror, f = 20 cm (It may be positive or negative according to the type of mirror)
Object distance = u
Image distance = v
Given magnification,
m = -v/u = ±h_i/h_o (the image may be erect or inverted)
For concave mirror,
f = - 20 cm
Image is inverted, so, -v/u = - h_i/h_o = -1/3
=> u = 3v
So, for a virtual, erect and diminished image a convex mirror is used, the image distance is 40/3 cm the object distance is -40 cm.

Suggest Corrections

Similar questions

Question 36
Size of image of an object by a mirror having a focal length of 20 cm is observed to be reduced to $\frac{1}{3} r d$ of its size. At what distance the object has been placed from the mirror? What is the nature of the image and the mirror?

6. a.An object 4 cm in size is placed at a distance of 25 cm from a concave mirror of focal
length 15 cm. Find the position, nature and height of the image.
b A converging mirror forms a real image of height 4 cm, of an object of height 1 cm
placed 20 cm away from the mirror. Calculate the image distance. What is the focal
length of the mirror?

At what distance from a concave mirror of focal length 25 cm should an object be placed so that the size of image is equal to size of the object.

Q. An object of size 7.0 cm is placed at 27 cm in front of a concave mirror of focal length 18 cm. At what distance from the mirror should a screen be placed so that a sharp focussed image can be obtained? Find the size and nature of image.

Join BYJU'S Learning Program