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Transformers, Car Coils and RC Circuits – Practice
1. Write down Maxwell’s equations.
2. A. What is
 
E
  dA ?
B. Give two specific examples where you would use
 
E
  dA to solve a problem. One
example should deal with electrostatics and the other when the situation is changing
with respect to time.
1.
2.
3. A. What is
 
B
  dA ?
B. What does


 B  dA
= 0 imply?
4. Name two ways that electric fields are created.
1.
2.
5. Name two ways that magnetic fields are created.
1.
2.
6. A generator supplies 100 V to a transformer's primary coil, which has 50 turns. If the
secondary coil has 500 turns, what is the secondary voltage?
7. A transformer has 500 primary turns and 10 secondary turns.
A. If Vp is 120 V (rms), what is Vs with an open circuit?
B. If the secondary now has a resistive load of 15 Ω, what is the current in the
primary?
C. If the secondary now has a resistive load of 15 Ω, what is the current in the
secondary?
8. The primary side of this step-up transformer has
5 windings. The secondary side has 20 windings.
A voltage of 100 V results in 10 A flowing through
the primary windings.
A. What is the power on the primary side?
B. What is the voltage on the secondary side?
C. What is the current on the secondary side?
D. What is the power on the secondary side?
9. The magnitude of the electric field between the two circular parallel plates is E = (4.0 ×
105) - (6.0 × 104t), with E in volts per meter and t in seconds. At t = 0, E is upward. The
plate area is 4.0 × 10-2 m2. For t ≥ 0,
A. What are the magnitude and direction (up or down) of the displacement current
between the plates?
B. What is the direction of the induced magnetic field clockwise or counterclockwise in
the figure?
Solutions:
2. A. electric flux
3. A. magnetic flux
6. 1.00 x 103 V
7. A. 2.4 V B. 3.2 x 10-3 A C. 0.16 A
8. A. 1.0 x 103 W B. 400 V C. 2.5 A D. 1.0 x 103 W
9. A. 2.1 x 10-8 A B. CW