Question

Sudheer wants to find focal length of a concave mirror experimentally. 

a) What apparatus does he need? 

b) Is the screen required or not? Explain.

c) Draw the table required to tabulate the values found in his experiment. 

d) What is the formula used by him to find focal length?

Answer 1

a) Apparatus required to Sudheer are

1.  Concave mirror, 
2.  White paper or screen, 
3.  Scale, 
4.  V – stand, 
5.  Candle. 

b) Yes, screen is required. To catch and measure the image distance screen is required.

c) 

Observation no.	Distance of the candle from the mirror (object distance(u))	Distance of paper from the mirror (Image distance(v))	Sign Convention		f = uv/u+v
			(u)	(v)
1.
2.
3.
4.

d) Focal length  \(\Rightarrow \)1/f =1/v +1/u (or) f= uv/u+v

This is the formula used by him to find a focal length.