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Name: ____________________________
Potential Drop Around The Circuit Lab
Purpose
In this lab, you will investigate the potential drop around a circuit.
Background
Kirchhoff's Loop Rule (also called Kirchhoff's Voltage Law or just the Loop Rule): The sum
of the potential differences across all circuit elements (following the loop rules of + and -) around
any closed loop is zero. This is also a statement of energy conservation in that any charge that
ends up at the same point it starts from with the same velocity must have no change in energy (e.g.
it loses as much energy as it gains).
In addition, the current at all points around a closed loop has the same value. This is also a
statement of charge conservation.
The potential difference used to move the charge around a circuit is called emf (formerly
known as electromotive force). The definition of emf is: E = dW/dq.
Ohm’s Law: I = V/R
Part I – Series Circuit
1. Select three resistors close to the same resistance. Measure the resistance of each and
record the results here:
R1
___________
R2
___________
R3
___________
2. Set the power supply voltage to 10 V. Set the current dial to midrange. Measure the set
voltage with a multimeter. Record the results here:
___________
3. Connect R1, R2 and R3 in series with the voltage source.
a) What is the measured potential difference across R1?
b) What is the measured potential difference across R2?
c) What is the measured potential difference across R3?
___________
___________
___________
d) Predict the potential difference across R1 and R2?
e) What is the measured potential difference across R1 and R2?
___________
___________
f) Predict the predicted potential across R1, R2 and R3?
g) What is the measured potential across R1, R2 and R3?
___________
___________
Analysis
1. How does the total potential drop across R1, R2 and R3 (i.e. V1 + V2 + V3) compare to the
voltage source? What law or rule does this support?
2. Calculate the total current Itot that flows through your circuit? Show your work.
3. Using your measured values of resistance and potential drop across each resistor, calculate
I1
____________
I2
____________
I3
____________
4. How does I1, I2 and I3 related to Itot? Explain.
Part II – Parallel Circuit
1. Now using the same three resistors as in Part I, connect them in parallel.
a) What is the measured potential difference across R1?
b) What is the measured potential difference across R2?
c) What is the measured potential difference across R3?
___________
___________
___________
Analysis
1. How does the total potential drop across R1, R2 and R3 compare to the voltage source? What
law or rule does this support?
2. Calculate the equivalent resistance of your circuit (neglecting any internal power supply
resistance). Show your work.
3. Calculate the total current that flows through your circuit? Show your work.
4. Using your measured values of resistance and potential drop across each resistor, calculate
I1 ____________
I2 ____________
I3 ____________
5. How does I1, I2 and I3 related to Itot? Explain.