Question

13. An object is placed 20cm from a concave mirror of focal length 15cm. Calculate the linear magnification of the image formed. *

a. 0.5
b. 1.5
c. 2.0
d. 3.0

Answer 1

V= UF/(U-F). U= 20cm F = 15cm

V= 20*15/(20–15) =+60cm

Magnification M = -(V/U) = - 60/20 =- 3

So V=60cm, virtual inverted and enlarged image will be formed behind the mirror at a distance of 60cm

Answer 2

Correct Answer Is Option (D) 3.0 Cm

GIVEN

Object distance = 20cm

Focal length = 15 cm

TO FIND

Linear Magnification of the image formed.

SOLUTION

We can simply solve the above problem as follows,

Linear magnification can be defined as the ratio of image height and object height measured in a plane that is perpendicular to the optical axis.

m = hi/ho

where,

m= linear magnification

hi = image distance

ho= object distance.

We can also calculate the linear magnification of the image by applying the following formula -

$m = \frac{f}{f- u}$

Where,

u = object distance (negative in case of a concave mirror)

f = focal length of the mirror. (negative in case of a concave mirror)

putting the values in the above formula we get,

$m = \frac{ - 15}{ - 15 + 20}$

m = -15/-5

m= +3 Cm

Since magnification is positive, this implies that the image formed is Virtual and erect.

Hence, The linear magnification of the image formed is 3.0 cm

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