Investigating the factors which Affect the image formed by a Convex lens

8. I repeated steps 1 to 7 twice in order to get an average.

RESULTS

LENS FROM OBJECT (cm)

LENS FROM SCREEN (cm)

1 2

AVERAGE

70

65

60

55

50

45

40

35

30

40

40

42

45

49

56

66

88

55

39

41

42

45

49

55

65

86

41

39.5

40.5

42

45

49

55.5

65.5

87

48

CONCLUSION- ANALYSIS

I have found out that the closer the light box is to the lens, the further away you have to place the screen in order to get a clear picture. I found also found out that the closer the lens is to the light box, the bigger the image created on the screen. The image was inverted for al distances. For example, the image created with the lens 32cm away from the light box is clear when the screen is 110cm away from the lens. The image created with the lens 61cm away from the light box is made clear with the screen 42cm away form the lens. On my graph, as well as my actual results, I plotted the theoretical results using the formula: 1 + 1 = 1

U V F

I had estimated the focus length of the lens I used was 20cm by projecting the light shone though a window through the lens and onto the screen. I then measured the distance between the screen and the lens. This method of finding the focus point was very inaccurate and probably was the reason for the difference in the actual and theoretical results. How ever, I can work out the actually focus of the lens by using the same formula and some of my results:

+ 1 = 1

U V F

+ 1 = 1

60 42 ?

7 + 10 = 17

420 420 420

= 1

24.7

The actual focal length of the lens I used was 25 (24.7 rounded up to the nearest whole number). From this I can see that my results were very accurate my results were only millimetres out.

My results support my prediction entirely.

CONCLUSION- EVALUATION

My evidence is strong enough to support a firm conclusion. I have confirmed the strength of my evidence by using a scientific formula that I have found in a physics textbook. Using this formula I could see my results were accurate. This shows that my evidence was reliable; as does the fact that I obtained no anomalous results.

However, the procedure was not entirely accurate. It was very hard to get the light box lens and screen to line up perfectly and I do not know if this affected my results in any way. To improve the experiment, I would like to have done the measuring with more accuracy. In this experiment I only took measurements using centimetres to no decimal places. If I did it again I would take the measurements using millimetres.

If I did the experiment again I would not only investigate one factor. I would also investigate the size of the image projected onto the screen when a clear picture has been obtained. I would also use more that one lens to see if a change in focus point would make that much of a change to the results.