Dusk-to-Dawn Light

We calculated the Voltage across Photocell V_b to be 1.7V for 5k(ohm) and 3.33V for 20k(ohm)

The setup.

When the Light sensor was exposed to light the V_b which is voltage across the photocell was .91V and V_d which is voltage across the LED light was 0.54.

After we covered the sensor, the V_b was 2.45V and V_d was 1.93V.

Summary: In this lab we created some device that lights up in dark and turns off at light. The photocell has high resistance when there is low light and low resistance when there is low light, and BJT (Bipolar Junction Transistors) is VCCS (Voltage controlled current source). That is why photocell provides high voltage to base of BJT in low light and low voltage or not enough voltage in bright light. This is why it turns off in bright light and turns on when we covered the photocell.