Transcript Experiment to measure the focal length of a concave mirror

Experiment to measure the focal
length of a concave mirror
Apparatus:concave mirror, screen, metre stick, light source with
cross threads.
Method:
1. Find a rough value for the focal length of the mirror by
finding the image of a distant object into a screen. The
distance from the screen to the mirror is then the rough
value of focal length.
2. Set up the apparatus as in the diagram keeping the distance
from the screen to the mirror greater than the rough value of
focal length. Adjust the position of the screen until a sharp
image if the cross threads is seen. Then measure the image
distance v and the object distance u.
3. Use the formula 1/f=1/u + 1/v to find f.
4. Repeat and find an average.
Another method involves plotting 1/u against
1/v and the value of 1/f is where the graph
cuts the x and y axis.
Results
u/cm
v/cm
f/cm
Precautions
Avoid parallax when measuring distances.
Repeat and average.