Question

consider the following ray diagram : PB'=10cm and PB=50cm. the focal length of the mirror is :
a) 8.33cm
b)25cm
c)12.5cm
d)2.5cm​

Answer 1

Answer:

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Object Distance(u) = 10 cm. (negative)

Focal length of the lens (f) = 5 cm.

We know, convex mirror always forms the virtual, upright and diminished.Also, Object distance in the convex mirror is always negative where as Image distance and focal length are positive.

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Answer 2

Explanation:

Given:

Image distance $PB^{'} =10 cm$

Object distance $PB =50cm$

To find: Focal length of the mirror

Calculation:

• Mirror shown in the figure is a convex mirror which produces an erect and virtual image of an object kept infront of the mirror.

• Convex mirrors are also called diverging mirrors. It reflects light outwards.

• Object distance is taken in the opposite direction of the incident ray and so it is negative.

• Image distance is taken in the direction of incident ray so it is positive.

Mirror formula:

$\frac{1}{f} =\frac{1}{u} +\frac{1}{v}$

$\frac{1}{f} =-\frac{1}{50} +\frac{1}{10} \\f=12.5 cm$

So, the focal length is $12.5cm.$

Answer:

The focal length is $12.5cm.$