To Determine the Focal Length of a Convex Lens.

* I will do the experiment twice for each measurement to ensure that the results are accurate

Safety:

Making sure that all bags are put under tables will make this experiment safe. Also the work surface will be cleared of all books and other mess, which will mean that the table will be empty and easier to work on. The bulb will be hot so I will make sure that no one touches it or looks directly at it because it will also be very bright.

Theory:

The distances from the lens to the screen (U) as well as measuring the distance from the lens to the projector (V) will make me think of a formula. I have obtained a formula for this: -

1 + 1 = 1 or 1 = -1 + P

U V F U V

AND

Problems that might arise:

In this experaments there might be a number of problems. For example the equipment might not be 100% accurate; this might effect my results, so I will do the experiment two or three times to ensure the results are accurate.

I will keep the bulb brightness the same all through out the experiment. I will also keep the projector in the same place, which is at zero on the optical bench. The optical lens I use will also stay the same.

In this experiment I will change the distance between the lens and the projector and I will also change the projector if there is a problem with it.

I will be measuring the distance from the lens to the projector and also from the screen to the lens. These measurements will be in .05 mm to ensure that the distances are as accurate as possible.

Results Table:

U (mm)

V (mm)

30

59.80

0.033

0.017

35

46.50

0.029

0.022

40

39.65

0.025

0.025

45

35.60

0.022

0.028

50

33.00

0.020

0.030

55

31.35

0.018

0.032

60

29.45

0.017

0.034

65

28.40

0.015

0.035

70

27.20

0.014

0.037

Conclusion:

I have come to the conclusion that the further that the length from the object to the optical lens (U) the less the distance from the lens to the screen (V). I can see this from my results and I also saw that the closer the lens to the object the smaller the object on the screen. I also have found out that if the object is to close to the lens the object can not be focused on to the screen, this is called virtual imaging (see below diagram).

I have not got any trends or odd results and I think that the experiment went as I had planed, except the results table I done was not going up in 5mm but was going up in 10mm which made the results not as accurate. There were no other problems.

I think that the experiment could not have gone any better then I planed.

Asif Ishaq