MATERIAL REQUIRED
Concave Mirror, Optical Bench
THEORY
A concave mirror is a spherical mirror with a reflective surface that curves inward, resembling the interior of a bowl or a cave. It is also known as a converging mirror because it causes parallel light rays to converge at a single point called the focus after reflecting off the surface.
If u, v and f represents object distance, image distance and focal length of a concave mirror respectively, the relation between them is given by;
1/f =1/v+1/u
PROCEDURE
- Mount concave mirror at the one end (0 cm scale) of optical bench with lens holder.
- Mount one needle as object at middle of optical bench.
- Mount another needle at the another end of optical bench with needle holder taken as image.
- Look at he object needle on the the mirror from image needle in front of the lens.
- The object needle must be seen as inverted.
- Try to make height of image an object image is equal.
- Try to conside tip of object and image needle by moving either image needle or object needle.
- Then remove parallax error by moving head and image needle together.
- If parallax error was removed then tip of object and image needle fixed with moving head i.e: they are not separated.
OBSERVATION
| S.N. | Position of Mirror(M) | Position of Object(O) | Position of Image(I) | Object distance (u)=O-M | Image distance (v)=I-M | m=v/u | 1/u | 1/v | 1/f=1/v+1/u | f | Mean f =Σf/n |
| 1 | 0 cm | 14.7 cm | 49.5 cm | -14.7 cm | -49.5 cm | 3.367 | -0.068027 | -0.020202 | -0.088229 | -11.33 cm | 11.33 cm |
| 2 | |||||||||||
| 3 |
RESULT
The focal length of given concave mirror is 11.33 cm.
CONCLUSION
Hence focal length of concave mirror was calculated by optical bench method
PRECAUTION
- Parallax error must be minimized.
- Distance must be measured accurately.