3/7 Dusk-to-Dawn Light

We were asked to predict the result if we attached a hotdog to a line cord and apply a 120 V potential across it.
The answer is the hotdog will slowly cook.
And then, we were asked to predict what will happen if we insert LEDs into the hotdog both parallel and perpendicular to the hotdog axis.
The answer is the LEDS parallel to the hotdog will light.


From the circuit above, find v0 and i0 in the circuit
We did in the white board, and we got:

v0 = 8V, i0=4A


From the picture above, we leaned how to create a Vout that we want by using different value of resistance in the circuit.

Dusk-to-Dawn Light

The picture above is the basic set up for this lab.
Equipment:
1. breadboard
2. photocell
3. resistor
4. Bipolar Junction Transistors (BJTs)
5. some wires
6. MOSFET
7. LED
8. voltmeter


1.
We applied KVL around the outer loop of the circuit to determine the voltage VB for photocell resistances of 5K and 20K.
We got for resistance of 5K, VB is equal to 1.67V
            for resistance of 20K, VB is equal to 3.33V
2.

The measured value of VB for photocell resistances of 5K ohms and 20K ohms are shown in the picture.
Compared to calculated value of VB, when it was under light, the difference is about 76%. When it was covered, the difference is about 42%.
The reason why the difference is so big is because the value of resistance for photocell is not 5K ohms and 20K ohms. It is 0.9K ohms and 10K ohms, which will give us a big difference.
3.

Summary

We discussed some example about dependent source, series resistors and voltage division, parallel resistors and current division, and we did one experiment--Dusk-to-Dawn Light. From all this practices, we had a clear idea about how resistors work in a circuit, and also, we knew how to create a Dusk-to-Dawn Light now!!