Suggest an experiment to find out the focal length of the lens.if you have a lens.
Answers
Explanation:
To determine the focal length by an auxillary plane mirror method :
If we are given a vertical stand , a plane mirror , a lens and a pin
WE CAN PROCEED AS FOLLOWS :
i. Place the lens L on the plane mirror M M' Kept on the horizontal surface of the vertical stand and arrange the pin P horizontally in the clamp
so that its tip is vertically above the centre O of the lens L as shown in figure.
ii. Adjust the height of the pin till it has no parallax with its inverted image as seen from vertically above the pin .
To check for parallax , keep the eye vertically above the tip of the pin P at the distance nearly 25 cm from it and move it sideways . If the pin and its image shift together then there is no parallax.
iii Measure the distance x of the Pin P from the lens and the distance Y of the pin from the mirror using a metre rule and a plumb line .
Calculate the average of the two distance .
This gives the focal length of the lens
f = X + Y / 2
iv. Take three difference observation after removing the parallax each time and find the mean value of focal length of the lens .
THANK YOU
