Question

Q5. During an experiment of formation of image using concave mirror
Position of mirror = 10 cm
Position of candle =50 cm
Position of screen=90 cm
Find the focal length of mirror and draw the ray diagram using these distance by assuming suitable
scale.

please tell fast​

Answer 1

Given:

During an experiment of formation of image using concave mirror

Position of mirror = 10 cm

Position of candle =50 cm

Position of screen=90 cm

To find:

Focal length of mirror.

Calculation:

Object distance = 50 - 10 = 40 cm.

Image distance = 90 - 10 = 80 cm.

Since , the images formed on the same site as that of the object , the sign of image distance will also be same as that of object distance (i.e. both will be negative).

Applying Mirror Formula:

$\therefore \: \dfrac{1}{f} = \dfrac{1}{v} + \dfrac{1}{u}$

$= > \: \dfrac{1}{f} = \dfrac{1}{( - 80)} + \dfrac{1}{( - 40)}$

$= > \: \dfrac{1}{f} = - \dfrac{1}{80} - \dfrac{1}{ 40}$

$= > \: \dfrac{1}{f} = \dfrac{ - 1 - 2}{80}$

$= > \: \dfrac{1}{f} = \dfrac{ - 3}{80}$

$= > f = - 26.67 \: cm$

So, focal length of mirror is 26.67 cm

Refer to attached diagram.