Experiment 4: Kirchhoff's Laws
To check whether Kirchhoff’s Laws actually work, you will set up the circuit shown, predict what
the currents ought to be, then measure the currents to see if your prediction was right.
Meters: The wires from a voltmeter should go to the two points you are finding the potential
difference between; that is, put it in parallel with the emf
source. An ammeter should be in series, so the current to be
measured flows through it. Never connect an ammeter in
parallel; its resistance is practically zero, so this would
create a “short circuit” and overload the meter.
Set up this circuit, using two power supplies, three different
resistors between 100 Ω and 1000 Ω and five digital
multimeters. Decide on values to use for E1 and E2 in the
range 1 V to 5 V. Do not turn the circuit on yet.
Use Kirchhoff’s laws to calculate I1, I2 and I3. Hint: Start
by looking for a loop which gives an equation with only one variable in it. Calculating the
uncertainties in the answers would be complicated. As a rough estimate, let’s say each I might be
off by 5% or .01 mA, whichever is larger.
Set two of the multimeters to read DC volts and the other three to read DC milliamperes. Starting
with their knobs all the way down (counterclockwise), turn on the power supplies then adjust them
as closely as possible to the E1 and E2 you chose. Record the currents. A current whose direction is
opposite that shown in the picture should be recorded as negative. Don't take the circuit apart before
the instructor accepts your paper, so you can double-check data if necessary.
In your conclusion, state whether what theory predicts matched observation.
PHY 122
Report on experiment 4: Kirchhoff's laws
DATA:
E 1 = ______________ , E 2 = ______________
R1 = ______________ , R2 = ______________ , R3 = ______________
Calculate the currents:
Measured I1 = ______________ , I2 = ______________ , I3 = ______________