Question

A.State the mirror formula for determining the focal length of spherical mirrors. Write the meanings of the symbols used.

B. An object is placed at a distance of 25 cm from a concave mirror of focal length 15 cm. Calculate the distance of the image from the mirror.

Answer 1

Explanation:

a...1/u+1/v=1/f. u means object distance v means image distance and f means focal length.

b.... u=-25,f=-15 ,v=?

then,

1/u+1/v=1/f

1/-25 +1/v=1/-15

1/v=1/-15+1/25

1/v=-5+3/75

1/v=-2/75

v=-75/2

v=-37.5

Answer 2

Answer:

A. Mirror formula -

f is focal length, u is object distance and v is image distance.

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

B. The distance of the image from the mirror is 37.5 cm

Explanation:

A. The mirror formula for determining the focal length of spherical mirrors,

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

where f is the focal length, u is the object distance and v is the image distance.

B. Given data :

Focal length ( f) = - 15 cm

Object distance (u) = -25 cm

To be calculated: Image distance (v)

Formula to be used : Mirror formula

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

Calculations :

$\frac{1}{( - 15)} = \frac{1}{( - 25)} + \frac{1}{v} \\ \frac{1}{v} = \frac{ 1}{( - 15)} - \frac{1}{( - 25)} \\ \frac{1}{v} = \frac{ - 1}{15} + \frac{1}{25} = \frac{ - 5 + 3}{75} = \frac{ - 2}{75} \\ v \: = \frac{ - 75}{2} = 37.5 \: cm$

Hence, The distance of the image from the mirror is 37.5 cm

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