a.
0.01 J
b.
360,000 J
c.
100 J
d.
6,000 J
e.
none of the above
48. The current in amperes drawn by the heater is
a.
0.1
c.
144,000
b.
10
d.
none of the above
49. The resistance in ohms of the heater is
a.
0.1
c.
144,000
b.
10
d.
none of the above
50. If two heaters are connected in parallel across the 120 volt source, the total power in watts
drawn from the source is
a.
600
c.
2400
b.
1200
d.
none of the above
51. If two heaters are connected in parallel across the 120 volt source, the current in amperes
drawn from the source is
a.
5
c.
20
b.
10
d.
none of the above
52. Why is most matter electrically neutral?
a.
It contains no charges.
b.
There are equal amounts of positive and negative charges present.
c.
The charge on the electrons and protons in the material is too small to notice.
d.
none of the above
53. Lightning is dangerous to humans because lightning strokes
a.
carry large currents
c.
have no resistance
b.
have high voltages
d.
fry whatever they hit
54. Why do you hear thunder a substantial time after seeing a lightning flash?
a.
The sound is produced later than the light is.
b.
Your eyes respond more quickly than your ears.
c.
The flash and thunder really are simultaneous, but the thunder lasts longer than the
flash.
d.
Sound travels much more slowly than light.
55. How come birds can land on overhead power lines without getting electrocuted?
a.
Their feet are good insulators.
b.
They are saved by their small size.
c.
Both their feet are on the same wire, so they don’t complete a circuit.
d.
They are just lucky, I guess.
56. You have a parallel circuit in a house that operates on 120 V with several outlets for
plugging in appliances and it has a 20 A fuse in the circuit. What is the maximum number of
600 W appliances that can be plugged into the outlets without “blowing” the fuse? Assume
that if the current flow exceeds the rating of the fuse, it will blow.
a.
2
c.
5
b.
4
d.
7
57. If you have 7 total 100 W light bulbs in a parallel circuit your basement and you leave them
on for 1.5 days, how much energy (in kilowatt hours) would be used?
a.
25.2 kWh
c.
3520 kWh
b.
1050 kWh
d.
25200kWh
58. A solid metal wire has a certain resistance. It is heated and carefully stretched to form a
longer, thinner wire. After it cools, the resistance is _______ than it was before.
a.
greater
c.
no more
b.
less
d.
lighter
59. A simple electrical circuit has a constant voltage power supply and a variable resistor as a
circuit. As you increase the resistance the current flow _____________
a.
increases
c.
remains the same
b.
decreases
d.
cannot be determined
60. Fuses and circuit breakers are used to prevent
a.
electrical shocks
c.
save on the cost of electricity
b.
fires overheating and causing fires
d.
to store energy
61. An electric motor on an airplane operates on 21.5 volts and draws a current of 11.0 amperes.
How much energy (in joules) does the motor use during a 9.0 hour flight?
a.
1064.4
c.
127710.0
b.
2128.5
d.
7662600.0
MULTIPLE RESPONSE
1. A battery supplies
a.
AC current
b.
DC current
c.
resistance
d.
voltage
e.
positive ions
2. What does a neutral atom become if it acquires an extra electron?
a.
negatively charged
b.
positively charged
c.
an ion
d.
a molecule
3. What force might a charge placed at location D feel?
a.
zero
b.
an upward force
c.
a downward force
d.
a force to the right
e.
a force to the left
4. Two charged bodies separated by a distance d exert a repulsive electrical force on each
other. The signs of the charges on the two bodies might be
a.
+ and +
b.
– and –
c.
+ and –
d.
any of the above
e.
not determinable
5. Ohmic heating is
a.
always undesirable
c.
what makes fuses “blow”
b.
used in light bulbs
d.
all of the above
6. The resistance of a wire can be increased by
a.
making the wire longer
c.
making the wire thinner
b.
lowering the temperature of the wire
d.
making the wire shorter
COMPLETION
NARRBEGIN: Heater 1200 watts
A heater is rated at 1200 watts for a 120 volt source.
NARREND
1. If two heaters are connected in parallel across the 120 volt source, the current drawn from
the source is __________.
2. The current drawn by the heater is __________.
3. The resistance of the heater is __________.
4. If two heaters are connected in parallel across the 120 volt source, the total power drawn
from the source is __________.
5. Like charges _________, unlike charges __________.
6. An atom with fewer electrons than protons is a __________.
7. The type of current supplied by a battery is __________.
8. In the U.S., AC line voltage oscillates at a frequency of __________.
9. An object that has zero resistance is a __________.
10. The rate of flow of electric charge is __________.
11. Superconductivity is lost when a certain __________ is exceeded.
12. A charged particle creates an electric ________ in the space around it.
13. Then energy per unit charge supplied by a battery is its __________.
14. A quantity that measures the opposition to the flow of charge is __________.
15. The size of the current flowing through a conductor equals the __________ divided by the
conductor’s ___________.
16. If you think of a battery as an electric charge “pump,” the battery voltage is analogous to
__________.
17. The force on a charged object divided by the charge on the object is __________.
18. Two charged bodies separated by a distance d exert an electrical force on each other. The
distance d is doubled. The electrical force on each body is now __________ times the
original force.
19. Two charged bodies separated by a distance d exert an attractive electrical force on each
other. The signs of the charges on the two bodies are __________ and __________.
20. Four things that the resistance of a conducting material depends on are __________,
__________, __________ and ___________.
21. If the length of a wire increases, its resistance __________.
22. If the diameter of a wire increases, its resistance __________.
23. If the temperature of a wire increases, its resistance __________.
24. If the voltage across the ends of a wire increases, the current in the wire __________.
25. AC voltages can be easily increased or decreased through use of a __________.
26. When a 12 volt car battery is short circuited with a wire, the current drawn from the battery
is 100 amperes. The resistance of the wire is __________.
27. A battery operating a large flashlight produces a current of 2 amperes in a light bulb that has
a resistance of 4 ohms. The voltage of the battery is __________.
28. An electric toaster operating on 120 volts draws a current of 6 amperes. The resistance of
the toaster is __________.
29. The resistance of the light bulb is __________.
30. The power consumed by the light bulb is __________.
31. If two slide projectors are connected in parallel across the same 120 volt source, the current
drawn from the source is __________.
32. If two slide projectors are connected in series across the same 120 volt source, the current
drawn from the source is __________.
33. The energy used by a 100 watt light bulb in 1 hour is __________.
34. The loss of usable energy in cables used to conduct electricity from power plants to citeis is
cause by ________________.
35. In a thunderstorm cloud, the concentration of negative charge is in the __________ portion
of the cloud.
36. A simple electrical circuit has a constant voltage power supply and a variable resistor as a
circuit. As you increase the resistance the current flow _______________.
MATCHING
Match each item with the correct statement below.
a.
AC
i.
repel
b.
attract
j.
resistance
c.
critical temperature
k.
semiconductor
d.
electric current
l.
transformer
e.
DC
m.
superconductor
f.
electric field
n.
voltage
g.
negative ion
o.
electric charge
h.
positive ion
p.
ohmic heating
1. superconductivity is lost when this is exceeded
2. an atom with fewer electrons than protons
3. type of current supplied by a battery
4. employed in toasters and fuses
5. has zero resistance
6. consists of charges flowing back and forth
7. rate of flow of electric charge
8. used to change AC voltages
9. the energy per unit charge supplied by a battery
10. like charges do this
11. it is measured in ohms
12. this phenomenon results in a loss of usable energy
PROBLEM
1. A battery in a large flashlight produces a current of 2 amperes in a light bulb that has a
resistance of 3 ohms. What is the voltage of the battery?
2. An electric toaster operating on 120 volts draws a current of 9 amperes. What is the
resistance of the toaster?
3. The light bulb used in a slide projector draws a current of 4 amperes when operating on 120
volts.
(a) What is the bulb’s resistance?
(b) What is the bulb’s power consumption?
4. How much energy does a 100 watt light bulb use in 1 hour? Express your answer in (a)
joules and in (b) kilowatt-hours. (c) Also find how much money it costs if electricity sells
for 10 cents per kW-h.
5. An electric motor on an airplane operates on 24 volts and draws a current of 15 amperes.
(a) What is the power consumption of the motor?
(b) How much energy does the motor use during a 2 hour flight?
6. The light bulb used in a lamp has a resistance of 240 ohms when operating on 120 volts.
What is the bulb’s power consumption?