Conduct an experiment to find out the focal length of the lens.
Aim: To find the focal length of the lens.
Requirements: Bi Convex Lens, Metre Scale, V Stand, Screen, an Object(i.e., Candle)
- Take a meter scale and keep it on a long table,
- Place the V-stand on the table along the meter scale.
- Keep the Convex lens on the V- stand along with the meter scale.
- Keep the object (i.e., Candle) in front of the lens and measure its distance from the lens and note it down on the table. (Say it is 5cm)
- Keep the White screen on the other side of the lens.
- Now, Light the candle and move the screen, so that you get a sharp image of the object on the screen.
- When you get the sharp image, stop moving the screen and note down the reading from the meter scale.
- Now, measure the distance of image (v) from the V- stand and note it down as image distance.
- And measure the distance of the object (i.e., candle ) from the V-stand and note it down as Object distance.
- Repeat the experiment by keeping the candle at various distances like 10cm, 20 cm etc.,
- Measure the object distance and image distance on each case and note it down in the table.
- Now, find out the focal length using the formula 1/f= 1/v-1/u.
- You will find that the focal length is equal in all cases.
- The value of ‘f’ is the focal length of the convex lens.
- No obstacle should be there in the path of the lens
- Record the image distance when you get a sharp and clear image on the White screen.
- Fix the lens vertically on the V-stand
- The base of the lens and white screen should be in line with the measuring scale.