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Experiment 3 (Series and Parallel Resistors)

TEE 2O0 - Mr. Caine

By: Kyle Koloszar and Christian Angulo


1. To investigate resistors in series.
2. To investigate resistors in parallel.


1. 1 (one) SK-50 breadboarding socket.
2. 1 (one) 9 volt battery.
3. 2 470  ohm resistors.
4. 1 (one) LED (Light Emitting Diode).
5. 3 wires.



1. Assemble the circuit (a) on the breadboard and observe the LED.
2. Assemble the circuit (b) on the breadboard and observe the LED.
3. Assemble the circuit (c) on the breadboard and observe the LED.



1. Describe the change in brightness of the LED for circuits (a), (b) and (c).

Circuit 3a, which had one (1) 470 ohm resistor, was used as a reference to the other two (2) circuits, 
so comparisons could be made. Circuit 3a was normally bright. Circuit 3b had two (2) 470 ohm resistors 
in series; this circuit was the dimmest compared to 3a and 3c. Finally, circuit 3c with two (2) 470 ohms 
in parallel. This circuit's LED was the brighest.

2. Use the formula for resistors in series and parallel to explain the observations.

Resistors have two formulas to calculate vales; when in series and when in parallel. The value of resistors 
in series can be calculated with: Rt=R1+R2+etc. This suggests that the total resistance is the total of all 
resistors in series. The value of resistors in parallel can be calculated with: Rt=1/{(1/R1)+(1/R2)+etc.}. 
This suggests that the value of the resistors is added up, then divided by one. This will produce a smaller 
resistor value than in series. In our experiment, resistors in series would have a total of 940 ohms, and a 
much dimmer LED compared to resistors in parallel, where the total resistance is 235 ohms; the brightest LED.

3. Suggest how 3 resistors in series or parallel would affect the observations in circuits (b) and (c).

If there were 3 resistors in series (circuit 3b), the resistance would be higher than it currently is, therefore 
a dimmer LED. However, if three resistors were placed in parallel (circuit 3c), the resistance would be lower, 
therefore a brighter LED.


Summarize the general results for networks of series and parallel resistors.

Resistors in series will tend to have a higher total resistance, based on the formulas, however, resistors in 
parallel tend to divide up the resistance, and therefore a lower total resistance.