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022
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Which of the following are characteristics of series circuits? Select all that apply.
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87
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028
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A 26 A fuse in a household circuit burns out. If fuses of only 24 A or 31 A were available to
replace it, which would be safer?
Correct. The purpose of a fuse is to burn out and stop current flow in a circuit if the current
becomes too high. Since the 24 A fuse would do this for any current above 26 A (and also any
current above 24 A), it should properly protect the circuit.
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will also stop functioning.
Correct.
There are multiple paths for current to follow
through the circuit.
The voltage across each device must be the same.
The voltage
is divided among all devices in the circuit.
Correct.
The same amount of current flows
through all devices in the circuit.
Correct.
There is only one path for current to follow
through the circuit.
Correct.
If one device in the circuit stops allowing current to flow, all other devices in the circuit
The 24 A fuse would be safer, since it is lower than the 26 A original.
The 31 A fuse
would be safer, since it is large enough to handle 26 A.
More information is needed.
The 24 A fuse might be better because it is closer to the 26 A original or the 31 A might
be better because it seems to have enough capacity.
1.79
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A current of
0.3 A
goes through an electric motor for
9 min.
How many coulombs of charge flow through it during that time?
C
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The resistance of each brake lightbulb on an automobile is
6.7
Ω
.
Use the fact that cars have 12-V electrical systems to compute the current that flows in
each bulb if they are connected in series. (For simplicity, assume that the circuit is only
composed of one brake lightbulb and the car battery.)
A
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All of the electrical outlets in a room are connected in a single parallel circuit. The circuit is
equipped with a 20-A fuse, and the voltage is
V
= 120 V.
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162
2400
1
(a) What is the maximum total power that can be supplied by the outlets without blowing
the fuse?
W
(b) How many 1,600-W appliances can be plugged into the sockets without blowing the fuse?
appliance(s)
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A solid metal cylinder has a certain resistance. It is then heated and carefully stretched to
form a longer, thinner cylinder. After it cools, will its resistance be the same as, greater than,
or less than what it was before? Explain your choice.
resistance.
The resistance will be greater since the resistance is proportional to length
and inversely proportional to cross-sectional area. Increasing the length and shrinking the
radius both act to increase the resistance.
The resistance will be less than before
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area. Increasing the length and shrinking the radius both act to decrease the resistance.
since the resistance is inversely proportional to length and proportional to cross-sectional
cross-sectional area. Increasing the length and shrinking the radius will not affect the
The resistance will be the same since the resistance is independent of the length and
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During
39 seconds
of use,
300 C
of charge flow through a microwave oven. Compute the size of the electric current.
A
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A lightning stroke lasts
0.02 s
and involves a flow of
239 C.
What is the current?
A
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A current of
24.3 A
flows through an electric heater operating on
120 V.
What is the heater's resistance?
Ω
10.
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7.69
11950
4.94
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the hair dryer
the lamp
1861500
1.57
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An electric eel can generate a
439-V, 0.8-A
shock for stunning its prey. What is the eel's power output?
W
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An electric train operates on 850 V. What is its power consumption when the current flowing
through the train's motor is 2,190 A?
W
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An electric clothes dryer is rated at 2,700 W. How much energy does it use in 35 min?
kWh
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Which costs more, running a 1,900-W hair dryer for 6 min or leaving a 40-W lamp on
overnight (10 h)?
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351.2
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The resistance of an electric heater is
80
Ω
when connected to 120 V. How much energy does it use during
40 min
of operation?
J
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014
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What would an audio speaker like that shown in the figure below do at the instant a low-
voltage battery is connected to it?
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432000
The speaker cone would only be pushed outward until the current stopped.
The
speaker cone would only be pulled inward until the current stopped.
The speaker
cone would either be pushed outward or pulled inward until the current stopped.
The
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speaker cone's motion is independent of the current and it would not move.
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Radio waves.
31828.95
783.78
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The generator at a power plant produces AC at 19,000 V. A transformer steps this up
to 295,000 V for transmission over power lines. If there are 2,050 turns of wire in the input
coil of the transformer, how many turns must there be in the output coil?
turns
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The blackbody radiation emitted from a furnace peaks at a wavelength of 3.7 10
-
6
m (0.0000037 m). What is the temperature inside the furnace?
K
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Which type of EM wave does your body emit most strongly?
Ultraviolet light. Infrared.
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The charger cord used to recharge a cell phone contains a transformer that reduces 120 V
AC to 5 V AC. For each 1,425 turns in the input coil, how many turns are there in the output
coil? (Round your answer to at least one decimal place.)
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Visible light.
Microwaves.
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turns
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Compute the frequency (in MHz) of an EM wave with a wavelength of 4.9 in. (0.1245 m).
MHz
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Three magnets are set next to each other on a table (see the figure below). If all of the
magnets are identical, are evenly spaced, and cannot rotate, what will happen to the middle
magnet if the poles are aligned as shown?
Correct. The magnet in the middle experiences a push to the right from the magnet on the far
left and an equal size push to the left from the magnet on the far right.
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Select all of the following descriptions that match what happens when a ferromagnetic
material is placed in an external magnetic field.
The magnet in the middle will remain motionless. The magnet in the middle will be
pushed to the
left
.
The magnet in the middle will be pushed to the
right
.
59.38
2409
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with magnetic fields.
The external magnetic field induces magnetic poles in the
ferromagnetic material.
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When a direct current flows through a straight length of wire, what is the direction of the
magnetic field that is produced near the wire?
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When an electric motor is attached to a power supply, the motor turns. What happens if the
electric motor is turned by means of some external action (such as by a handle that is
attached to the axle of the motor)?
The ferromagnetic material becomes magnetized. The ferromagnetic material rapidly
cools. The ferromagnetic material becomes negatively charged. The ferromagnetic
material becomes positively charged.
Nothing, ferromagnetic materials do not interact
The magnetic field is
antiparallel
to the direction of the current. The magnetic field
is
perpendicular
to the direction of the current. The magnetic field is
parallel
to
the direction of the current. There is no magnetic field near a wire carrying direct
current; direct currents do not create magnetic fields.
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current.
The motion of the motor induces an electric current, and the motor functions
Nothing. Without an electrical input the motor is not able to produce motion or an electric
as a generator.
The motion of the motor produces a short burst of electric
current when the handle is first turned, but the current slowly drops to zero, even if the
handle is turned continuously. The motion of the motor induces an electric current,
but only if the motor is turned extremely slowly.
.
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