Section 25.2
Changing Magnetic Fields Induce EMF
Practice Test
1.
A step-down transformer has 80,000 turns on its primary coil and 500 turns on its secondary coil. If the primary coil is attached to a generator with an
EMF
of 45.0 V, what is the
EMF
in the secondary coil?
a.
1.39×10
-4
V
b.
3.56 V
c.
0.281 V
d.
7.20×10
3
V
Hint
2.
What happens to the secondary current in a step-up transformer?
a.
It remains the same.
b.
It increases.
c.
It decreases.
d.
It is not affected.
Hint
3.
A transformer is a device to increase or decrease AC __________.
a.
power
b.
heat
c.
voltage
d.
resistance
Hint
4.
__________ is (are) generated when a piece of metal moves through a magnetic field.
a.
Lenz's laws
b.
EMF
c.
Voltage drop
d.
Eddy currents
Hint
5.
In Figure 25-13a, if the primary coil were increased to 10 turns while its voltage and current were kept the same, what effect would this have on the secondary coil?
a.
Its number of turns would increase.
b.
Its power would increase.
c.
Its voltage would decrease.
d.
Its current would decrease.
Hint
6.
Electricity sent over power lines needs __________.
a.
low voltage and high current
b.
high voltage and high current
c.
high voltage and low current
d.
low voltage and low current
Hint
7.
In Figure 25-13a, if the primary coil's current were increased while its voltage was kept the same, what effect would this have on the secondary coil?
a.
Its voltage would decrease.
b.
Its power would decrease.
c.
Its current would increase.
d.
Its number of turns would increase.
Hint
8.
In Figure 25-13a, if the primary coil's voltage were increased while the current were kept the same, what effect would this have on the secondary coil?
a.
Its number of turns would increase.
b.
Its power would decrease.
c.
Its voltage would increase.
d.
Its current would decrease.
Hint
9.
A step-up transformer has 400 turns on its primary coil and 1000 turns on its secondary coil. If the secondary coil has a current of 1.30 A, what is the current in the primary coil?
a.
0.520 A
b.
1.62 A
c.
7.75 A
d.
3.25 A
Hint
10.
A transformer goes from 10 V to 5000 V. How do the number of loops relate in the different coils?
a.
There are 500 times more loops in the secondary coil.
b.
There are 500 times more loops in the primary coil.
c.
There are 5000 times more loops in the primary coil.
d.
There are 50 times more loops in the secondary coil.
Hint
11.
A carpenter turns on the power to a table saw in his workshop. The lights dim and return to full brightness after the motor is going at full speed. Why does this occur?
a.
back-
EMF
of the light
b.
back-
EMF
of the motor
c.
a short circuit
d.
a short reduction in voltage due to the power company
Hint
12.
According to Lenz's law, the resulting force produced by an induced current __________.
a.
opposes the motion of the wire
b.
contributes to the motion of the wire
c.
reduces the resistance
d.
opposes the current
Hint
13.
In a transformer, the primary coil has twice as many loops as the secondary coil. This is a __________ transformer.
a.
reduction
b.
voltage
c.
step-up
d.
step-down
Hint
