Describe an activity to find the approximate value of focal length of focal length of a cocave mirror
Answers
To find the focal length of convex mirror and concave lens, you will need to use the mirror formula.
Here is an activity to find approximate value of focal length of concave mirror :-
1.Fix concave mirror to mirror holder and place it on a plane surface (say a long table). Turn the face of mirror towards a distant object (may be candle).
2.Now adjust the screen ,candle and the mounted concave mirror so that they are all on the principal axis.
3.Move the screen back and forth and determine the position for the brightest clearest image
4.Measure the distance between the concave mirror and the screen with a metre scale. Record your observations in observation table.
5.Repeat the experiment two or three times and find the mean value of the focal length.
Theory
How to find focal length of concave mirror?
Following are the ways to obtain the focal length of the concave mirror:
A concave mirror is defined as the spherical mirror whose reflecting surface is curved inwards and follows laws of reflection of light.
The light rays coming from a distant object can be considered to be parallel to each other.
If the image formed is real, inverted and very small in size, then the parallel rays of light meet the point in the front of the mirror.
f is used to denote the difference between the principal axis P and the focus F of the concave mirror.
To determine focal length of a given concave mirror
Materials Required
A concave mirror
A measuring scale
A screen holder
A mirror holder
A mirror stand
Procedure
1.The distance between the selected distinct object should be more than 50 ft.
2.The concave mirror placed on the mirror stand and the distant object should be facing each other.
3.The screen should be placed in front of the reflecting surface of the mirror. To obtain a clear, sharp image the screen should be adjusted.
4.Using a metre scale the distance between the concave mirror and screen can be determined. The distance is the same as the focal length of the given concave mirror.
5.Repeat the above procedure thrice to calculate the average focal length
