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Introduction to Physics IV
Exam 2 Review
March 22, 2013
During the exam, you can use:
 Single-sided sheet of notes (notebook paper sized)
 Calculators
You should know how to do the following:
1. Use Faraday’s Law.
2. Calculate the magnetic energy stored in a circuit.
3. Calculate the current at a given time for a circuit with a DC EMF source, resistor, and inductor.
4. Sketch a plot of current vs. time, calculate current.
5. Calculate inductive reactance, capacitive reactance, and impedance.
6. Calculate the amplitude of the voltage and current across a capacitor, inductor, and or resistor.
7. Calculate the EMF as a function of time or calculate the EMF at a particular time.
8. Calculate the voltage, current, or number of turns in the primary or secondary coil of a
transformer.
For a better chance of getting full credit, you should follow the following problem solving steps:
Draw Picture: Pretty self-explanatory. Draw a picture and label all knowns and unknowns, if applicable.
List knowns: List all of the information from the problem and give each number a variable.
List unknowns: List the quantity(ies) you will solve for. Assign each a variable.
Explain in words and/or equations how you will solve this problem:
Solve problem: Show all of your work in a clear, logical order. Label units.
Answer: Box your answer.
Does this answer make sense (order of magnitude?), have UNITS!!!!? , include all parts (vector or
directions, etc.)? This step is to make sure your answer is complete and reasonable.
Here are a few problems like the ones that you may see on the exam.
1. Suppose you have a DC power supply that supplies a voltage of 15 V in series with an inductor (L
= 25 mH) and a resistor (R = 100 ohms). If you connect the circuit at t = 0.0 s, what is the current
through the circuit at t = 0.01 s?
2. Suppose you have an EMF AC source in series with a capacitor and an inductor. Assume the
frequency doubles. Answer the following questions:
a. The inductance of the inductor will (a) double, (b) not change, (c) halve, (d) quadruple.
b. The inductive reactance of the inductor will (a) double, (b) not change, (c) halve, (d)
quadruple.
c. The capacitance of the capacitor will (a) double, (b) not change, (c) halve, (d) quadruple.
d. The capacitive reactance of the capacitor will (a) double, (b) not change, (c) halve, (d)
quadruple.
3. A circular loop of wire is placed in a magnetic field of 0.300 T while the free ends of the wire are
attached to a 15.0 ohm resistor. When you squeeze the loop, the area of the loop is reduced at
a constant rate from 200.0 to 100.0 cm2 in 0.0200 s. Using Faraday’s law, find the magnitude
and direction of the current in the resistor.
4. A series RLC circuit is connected to a source of alternating emf. The components have values R =
3.00 ohms and C = 20.0 x 10-12 F, and a resonant frequency f = 17.0 MHz is connected to an
alternating emf source with max = 12.0 V. (a) What is the amplitude of voltage across the
inductor at resonance? (b) What is the amplitude of the voltage across the capacitor at
resonance? (c) What is the voltage across the resistor at resonance? (d) What is the impedance
of the circuit? (e) What is the energy stored in the capacitor? (f) What is the energy stored in the
inductor?
5. True or false:
a. A transformer is used to change frequency.
b. A transformer is used to change voltage.
c. A transformer is used to change current.
d. The standard household wall-outlet voltage in Europe is 220 V, about twice that used in
the United States. If a European traveler wants her hair dryer to work properly in the
United States, she should use a transformer that has more windings in its secondary coil
than in its primary coil.
6. See next sheet.