The
Focal Length of a Concave Mirror
In an experiment to measure the focal length of a concave mirror the following values were found:
|
u/m |
0.12 |
0.15 |
0.17 |
0.2 |
0.24 |
0.285 |
0.326 |
|
v/m |
0.172 |
0.138 |
0.125 |
0.11 |
0.105 |
0.095 |
0.093 |
By drawing a suitable graph, calculate a value for the focal length, f.
SOLUTION
|
1/u / m-1 |
8.3 |
6.7 |
5.9 |
5.0 |
4.2 |
3.5 |
3.1 |
|
1/v / m-1 |
5.8 |
7.2 |
8.0 |
9.1 |
9.5 |
10.5 |
10.8 |
Graph 1/u against 1/v.
Draw the best straight line.
Use this line to obtain a single value for 1/u and 1/v.
From the graph, we get 1/u = 4 and 1/v = 9.9.
This gives 
i.e. 