Aim : Determination of focal length of bi - convex lens using UV method. 

Material Required : V stand, convex lens, light source, screen, meter scale etc. Take a V-stand and place it on a long (nearly 2m) table at the middle. Place a convex lens on the V-stand. Imagine the principal axis of the lens. Light a candle and ask your friend to take the candle far away from the lens along the principal axis. Adjust a screen (a sheet of white paper placed perpendicular to the axis) which is on other side of the lens until you get an image on it. 

Procedure :

(1) Take a V-stand and place a convex lens on this stand. 

(2) Imagine the principal axis of the lens. 

(3) Light a candle and ask your friend to take the candle far away from the lens along the principal axis. 

(4) We use a screen because it forms a real image generally which will form on a screen. Real images cannot be seen with an eye. 

(5) Adjust the screen, on the other side of lens until clear image forms on it. 

(6) Measure the distance of the image from the stand and also measure the distance between the candle and stand of lens. 

(7) Now place the candle at a distance of 60 cm from the lens such as the flame of the candle lies on the principal axis of the lens. 

(8) Try to get an image of candle flame on the other side on a screen. 

(9) Adjust the screen till you get a clear image. 

(10) Measure the distance of image (v) from lens and record the value of 'u' and 'v' in the table. 

(11) Repeat this for various distances of images; in all cases note them in the table. Observation :

Conclusion : From this we conclude that a convex lens forms both real and virtual images when object is placed at various positions.