Question

The focal length of a concave mirror is f and the
distance of the object from the principal focus is a. The magnitude of magnification obtained will

Answer 1

Answer:

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Class 12

>>Physics

>>Ray Optics and Optical Instruments

>>Problems on Mirror and Magnification Formula

>>The focal length of a conca...

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The focal length of a concave mirror is f and the distance from the object to the principal focus is p. The ratio of the size of the real image to the size of the object is:

Hard

Solution

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Correct option is

A

−

p

f

Distance of object is u=−(f+p)

v

1

+

u

1

=

f

1

gives:

v

1

−

f+p

1

=−

f

1

or,

v

1

=−

f

1

+

f+p

1

or,

v

1

=−

(f+p)×f

p

or, v=−

p

(f+p)×f

(-ve sign indicates image is real)

Magnification =−

u

v

=−

p×(f+p)

(f+p)×f

=−

p

f

(-ve sign indicates inverted)

So, ratio of size of image to that of object is: −

p

f