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Extra Review Problems for Electromagnetism
1. Three 425 F capacitors are connected in parallel to a 6.00 V battery. What is the
equivalent capacitance? What is the charge on each capacitor? What is the voltage on each
capacitor? a) 1275 μF b) 2.55 mC c) 6.00 V
2. Three 425 F capacitors are connected in series to a 6.00 V battery. What is the equivalent
capacitance? What is the charge on each capacitor? What is the voltage on each capacitor?
a) 142 μF b) 0.850 mC d) 2.00 V
3. Three 425 F capacitors are connected in the combination shown
to a 6.00 V battery. What is the equivalent capacitance? What is
the charge on each capacitor? What is the voltage on each
capacitor? a) 283 μF b) Parallel: 0.85 mC, Series: 1.70 mC
c) Parallel: 2.00 V Series: 4.00 V
4. A 425 F capacitor is charged to 6.00 V. It is then discharged
through a 20.0 M resistor. A) Find the time constant. B) Find the
initial charge on the plates. C) Find the charge on the plates exactly one time constant after
discharge has begun. D) What percent of the original charge is this? E) Find the capacitor’s
voltage 4250 s after discharge begins. F) Find the instantaneous current at t = 4250 s. G)
Find the half-life of the capacitor’s voltage. a) 8500 sec b) 2.55 mC c) 0.938 mC
d) 36.8% e) 3.64 V f) 1.82 x 10-7 A g) 5890 sec
5. Sketch a bar magnet with its magnetic field lines. Be sure to label the poles correctly.
6. Sketch the magnetic field lines in the solenoid shown here. Assume the current
enters on the left and exits on the right. Explain how the right hand rule works.
7. A +32 C charge having a velocity of 2.5104 m s-1 enters an external magnetic
field having a magnetic flux density of 0.75 T. Find the magnitude of the
magnetic force acting on the charge as it is in the field. Sketch in the
direction that the charge will follow as it passes through the field. Explain
how the right hand rule works. What will its speed be when it exits the
field? a) 0.60 N constant radial centripetal force b) describes a circular
path whose radius depends on the mass of the particle c) Fingers into
page, thumb down, palm faces right (for initial F) d) same speed upon
exiting
8. The diagram shows three parallel wires P, Q, and R, each having the
same current I. What is the direction of the resultant force on wire Q due
to wire P and wire R? Net force is towards P
9. A wire having a length of 20.0 m is propelled through the air in a direction perpendicular
to its length at 150. m/s in a magnetic field that is perpendicular to the plane of its velocity,
and having a strength of 0.015 T. A) What is the induced emf in the wire? B) If a resistor
of 12.0  is connected to the ends of the wire, what will its current be? C) What would be
the power dissipated in the resistor? a) 45.0 V b) 3.75 A c) 169 W
10. A coil of wire resting on a tabletop and having 100 turns and an area of 3.14 cm 2 is
immersed in a magnetic field (0.90 T) which is pointing upward. A) What is the angle that
the magnetic field makes with the direction of the area? B) What is the flux through a single
loop? C) What is the flux linkage through the coil? D) What is the induced emf if the
magnetic field remains constant? E) If the magnetic field decreases to 0.45 T in 0.25 s,
what is the rate of change of the flux linkage through the coil? F) What, then, is the induced
emf? G) What is the direction of the induced current in the coil, as viewed from above the
table? H) Which law tells you this?
a) 0° b) 2.83 x 10-4 Wb c) 2.83 x 10-2 Wb d) 0 V e) -0.0565 V f) 0.0565 g) CCW
h) Lenz’s Law
11. A coil having 250 turns is subjected to a time-dependent magnetic flux
as shown in the graph. A) What is the flux at t = 0.0015 s? B) What is
the flux linkage at t = 0.0015 s? C) What is the magnitude of the emf
induced in the coil? a) 1.5 x 10-3 Wb b) 0.375 Wb c) 250 V
I/A
em f / V
12. The graphs of voltage and current for an ac circuit containing a resistor are shown.
A) Find the rms voltage corresponding to the
40
induced emf whose graph is shown.
B) Find the peak voltage.
20
C) Find the angular frequency of the coil that
20
40
0
is producing this emf.
30
10
t / ms
D) Find the maximum flux linkage of the coil
-20
that is producing this emf.
E) Find the rms current from the graph.
-40
F) Find the peak current.
2
G) Write the equation which shows the time
variation of the current.
1
H) Find the resistance of the circuit.
20
40
0
I) What is the average power dissipated by the
30
10
t / ms
circuit?
-1
a) 28.3 V b) 40 V c) 314 rad/s d) 0.127 Wb
e) 1.41 A f) 2 A g) I = 2Asin[(314rad/s)t]
-2
h) 20  i) 40 W
13. A transformer having 250 turns in its primary winding has a 60
Hz input voltage of Vin = 120 VAC. It is desired that Vout should
be 16 VAC. A) How many turns should the secondary winding
have? B) If the current in the primary winding is 1.25 A, what
will the current in the secondary winding be? C) What is the
frequency of the output voltage? D) If the frequency doubles,
describe how this will affect power losses. a) 33 b) 9.38 A
c) 60 Hz d) It won’t.
Vin
Primary
Vout
Secondary