Question

A concave mirror has a focal length of 20 cm.

(a) What is its radius of curvature?
(b) At what distance from the mirror must an object and an image be so that the magnification 1S
(c) Where is the image for an object distance of 15 cm? What kind of image is it?
(d) For what range of object distances is the image larger than the object? For what part of this range is the image real and for what part is it virtual?

Answer 1

Step-by-step explanation:

a )

focal length of mirror = 20 cm

a ) radius of curvature = 2 x focal length = 2 x 20 = 40 cm

b )

c ) object distance u = 15 cm

image distance v = ?

focal length f = 20 cm from the formula

`(1)/(v) + (1)/(u) = (1)/(f)`

`(1)/(v) + (1)/(- 15) = (1)/(-20)`

v = + 60 cm

So image is magnified . It will be formed on the other side of the mirror .It will be virtual .

d )

The image is magnified when object is placed between 2 f and f or between centre of curvature and focal length . In this case image is real and magnified . The image is magnified when object is placed between focal length and the pole . In this case image is virtual .