PLC Activity #7
Resistive Circuits
Due: see website for due dates
How to get credit for this activity
First, sign-in at the computer and sign-out when the activity is complete. Show your work
and results to a PLC tutor so they can check your work and initial the signoff sheet. Be
prepared to answer questions about the activity or your results.
Part 1: DC Circuit Physlets
Go to Chapter 30: DC Circuits. Do the following Physlet Physics exercises and answer
the questions listed.
Problem 30.3
Answer the following questions for each circuit in this animation. Assume an ideal
battery (no internal resistance) and ideal meters but note that the battery and unknown
resistor are different for each circuit (electric potential is given in volts and current is
given in mA). Use the slider to change the variable resistor.
a. What is the resistance of the unknown resistance and the voltage of the battery in
each circuit?
b. What is the range of power dissipated for each circuit over the full range of variable
resistance values?
Problem 30.4
Rank the three resistors (from smallest to largest) in each of the two circuits (ammeter
current is given in amperes).
a. Circuit 1
b. Circuit 2
Physlet Problem 30.6
What is wrong with these circuits? Close the switches to see what happens and then
explain what is wrong. Note which circuit elements are destroyed (electric potential is
given in volts and resistance is given in ohms). Choose a new circuit after a circuit
element is "destroyed."
a. Circuit 1
b. Circuit 2
c. Circuit 3 (Hint: What might the power rating be on the resistor?)
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Part 2: Conceptual and Ranking Problems
Question 1
In the circuit the narrow resistor is made of the same material as the thick connecting
wires. Assume steady state.
a. Which graph (1a – 1f) correctly shows the magnitude of the E-field at locations
around the circuit? Explain your answers.
b. Which graph (2a – 2f) correctly shows the drift speed of the electrons at locations
around the circuit? Explain your answers.
Question 2
In the circuit the narrow resistor is made of the same material and is half as thick as the
thick connecting wires. Assume steady state. Before attempting to answer these
questions, draw a copy of this diagram.
a. (i) On your diagram, show the E-field at the locations indicated, paying attention to
relative magnitude. (ii) Is the field larger at point D or G? By how much larger is it?
(iii) Is the drift velocity larger at point D or G? By how much larger is it?
b. (i) Carefully draw pluses and minuses on your diagram to show the approximate
surface charge distribution that produces the E-field you drew. Make your drawing
show clearly the difference between regions of high (and low) surface charge
density. (ii) Which region has the highest and lowest surface charge density?
c. Use your diagram to determine which of the following statements about this circuit
are true. Explain your answers.
1. There is a large gradient of surface charge on the wire between locations C and E.
2. The electron current is the same at every location in this circuit.
3. Fewer electrons per second pass location E than location C.
4. The magnitude of the E-field is the same every location in this circuit.
5. The magnitude of the E-field at location D is larger than the magnitude of the Efield at location G.
6. There is no surface charge at all on the wire near location G.
Part 3: Mystery Circuits
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There are three mystery circuits that consist of an unknown combination of series and
parallel connections. You should try the following experiments to aid in your
investigation: remove one lamp from its socket and see how it affects the brightness of
the remaining lamps or short out one lamp and see how it affects the brightness of the
remaining lamps. For each mystery circuit, discuss the results of the above experiments
with your group members and then draw your best guess for how the lamps are
connected.
Mystery Circuit 1:
Mystery Circuit 2:
Mystery Circuit 3:
Mystery Circuit 4:
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