Electric Circuits unit test
A test on this unit alone, marked as a percentage and a letter grade — for the test your class is actually sitting, rather than for May. Answer everything, then submit once: seeing the answer to question 3 before attempting question 4 makes the final percentage meaningless.
Power supplied vs dissipated
Sign conventions in the loop rule
Ammeter and voltmeter placement
Real vs ideal battery
Kirchhoff's rules
Number of independent equations
When reduction fails
Ohm's law and its limits
Non-ohmic devices
Internal resistance
Resistivity and resistance
Power dissipation
Short answer 1. Define or explain: Brightness of bulbs
3 ptsShort answer 2. Define or explain: Reducing a network
3 ptsShort answer 3. Define or explain: Current density and drift velocity
3 ptsShort answer 4. Define or explain: Maximum power transfer
3 ptsFree response
10 ptsA 12 V battery of negligible internal resistance, a switch, a 50 kΩ resistor, and an initially uncharged 20 μF capacitor are connected in series. The switch is closed at t = 0.
Determine the current immediately after the switch is closed and the final charge on the capacitor.
Apply Kirchhoff’s loop rule to obtain the differential equation for q(t) and show by substitution that q(t) = CV(1 − e^(−t/RC)) is its solution.
Determine the time constant and the time required for the capacitor to reach half its final charge.
Determine the final energy stored in the capacitor and the total energy delivered by the battery, and account for the difference.
The 50 kΩ resistor is replaced by a 100 kΩ resistor. State how the final charge and the charging time change, with justification.