Physics 261
Simple Parallel Resistor Circuits
• Consider the following three ciruits (note that each placement of the ammeter is a separate
circuit):
In terms of the labels, R1 and R2 , calculate the total resistance, RT . In terms of R1 and R2 and
their uncertainties, σR1 and σR2 , calculate the uncertainty σRT by propagating uncertainties
(use the partial derivative method in your notes). This should be done and entered into your
notebook before arriving to perform the experiment.
• Assuming the power source is set to a potential difference E ± σE , predict, in terms of R1 , R2 ,
and E, the current through each resistor separately and through the entire circuit. Propagate
uncertainties to get the uncertainty for each current. This should be done and entered into
your notebook before arriving to perform the experiment.
• Select a 5.1 kΩ (nominal) resistor and a 10 kΩ (nominal) resistor. Note the color sequence and
nominal precision of each.
• Measure the resistance of each resistor and note the readings along with associated uncertainties. Do measurements and nominal values agree? Justify quantitatively.
• Plug the measured values into your formulas for total resistance and uncertainties.
• Assemble the circuit and set the power supply to around 10 volts. Record the actual setting
and, using the specification tables, determine the uncertainty.
• With the given voltage calculate the current expected through each resistor and the total
circuit, propagating uncertainties.
• Measure the current through the 5.1 kΩ resistor. Through the 10 kΩ resistor. Through the
entire circuit.
• Do measurements and calculations agree?
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