Lab 6: From Dusk Till Dawn


Lab 6: From Dusk Till Dawn

In this lab we created a simple circuit using a breadboard, resistors, a transistor, a photocell, and an LED.



A power supply is connected to the circuit. When the light levels are low, the photocell has a very high resistance and at high light levels it has a low resistance. The BJT acts as a switch in this circuit. When it is dark, the photocell has a high resistance which causes current to flow through the LED causing it to light up. When it is bright in the room, the photocell has a low resistance and the BJT sends no current through the LED. 

For the pre-lab we calculated the voltage, VB across the photocell with a resistance of 5k ohm and 20k ohm, respectively. 


We operated the circuit and measured voltage across the photocell.




Measured voltage with the photocell covered was 3.2 V versus 3.33 V predicted.

Measured voltage with the photocell uncovered was 1.1 V versus 1.7 V predicted.

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