course Phy 202
Experiment 28: Image FormationFocal Lengths
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Double Convex lenses
100 mm = 10 cm
50 mm = 5 cm
I used the 50 mm in the following:
Single Image of Candle:
Data:
Initial – Distance from screen to lens: 6.5 cm
Distance from candle to lens: 20 cm
50 cm from candle to lens:. 5 cm screen to lens
40 cm from candle to lens:. 5.6 cm screen to lens
30 cm from candle to lens:. 6.0 cm screen to lens
20 cm from candle to lens:. 6.5 cm screen to lens
Images of Double Light source:
50 cm from candles to lens
5.2 cm from lens to screen
4.7 cm of separation between flames
.9 cm separation between images
When left flame is blocked the right image disappears.
30 cm from candles to lens
5.7 cm from screen to lens
4.2 cm of separation between flames
1.2 cm of separation between images
20 cm from candles to lens
6.1 cm from screen to lens
4.7 cm of separation between flames
2 cm of separation between images
Within 3 cm of focal length
8 cm from candles to lens
7.2 cm from screen to lens
4.7 cm of separation between flames
6 cm of separation between images
Outside focal length by 1 cm
6 cm from candles to lens
4.5 cm from screen to lens
4.7 cm of flame separation
5 cm between images
Spotlight
The only way I could form a clear, bright spotlight was to place the candle 3 cm from the lens.
The sharpness and size decrease and the distance between the lens and light source increase.
Create an Image
40 cm away
Height of object: 6.2 cm
Height of image: 12.8 cm
Distance from 2nd lens: 47.1 cm
Distance from screen: 44.5 cm
30 cm away
Height of object: 6.2 cm
Height of image: 10.9 cm
Distance from 2nd lens: 52.6 cm
Distance from screen: 34.5 cm
Analysis
1/f = 1/i + 1/o
Single Candle Image:
1/5 = (1/50) +(1/5)
.2 = .22 – close but not exact
1/5 = (1/40) + (1/5.6)
.2 = .203
1/5 = (1/30) + ( 1/6)
.2 = .2
1/5 = (1/20) + (1/6.5)
.2 = .187
Double Candle Image:
1/f = (1/o) + (1/i)
1/5 = (1/50) + (1/5.2)
.2 = .21
1/5 = ( 1/30) + (1/5.7)
.2 = .208
1/5 = (1/20) + (1/6.1)
.2 = .21
1/5 = (1/8) + (1/7.2)
.2 = .25
1/5 = (1/6) + (1/4.5)
.2 = .38
Create an Image
i/o = image size/object size
47.5/44.5 = 12.8/1.06
1.06 = 2.06 – not as close as I would have liked
52.6/34.5 = 10.9/6.2
1.52 = 1.75
The evidence that the two candles are inverted is that at any distance when you block the light from the left candle the image on the right of the screen disappears.
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This is OK. Let me know if you have questions.