Lab 3: Dust to Down light

Dust to Down light

Pre-lab : We are asked to calculate the actual voltage across the photocell. When it is dark, it has a resistance of 20k, and has a voltage of 3.33v.  When it is light, it has a resistance of 5k, and has a voltage of 1.67v.

This is the set up of the experience. At room light, it does not light up.

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2. This is the voltage across the resistor when there’s light. Our experimental value is 0.67 V, while our theoretical value is 1.67 V. 

% difference: (1.67-0.67)/1.67*100%=-59.88%

This is the voltage across the resistor when there’s not light. Our experimental value is 2.74 V, while our theoretical value is 3.33 V. 

% difference: (3.33-2.74)/3.33*100%=-17.78%

The % difference is too big, because the actual resister for LED is 3.5K and 27.5K when light and on light.

Here is a video about our experiment.