PHYS101 HW: Electricity and Magnetism
Liberty University
1.[3/3 Points] Which of the following are characteristics of series circuits? Select all that apply.
The voltage is divided among all devices in the circuit.Correct.
There is only one path for current to follow through the circuit.Correct.
The same amount of current flows through all devices in the circuit.Correct.
If one device in the circuit stops allowing current to flow, all other devices in the circuit will also
stop functioning.Correct.
Correct: Your answer is correct.
2.[2/2 Points] A 26 A fuse in a household circuit burns out. If fuses of only 24 A or 32 A were
available to replace it, which would be safer?
The 24 A fuse would be safer, since it is lower than the 26 A original.
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.
3.[2/2 Points] 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?
162 C
Correct: Your answer is correct.
4.[2/2 Points] The resistance of each brake lightbulb on an automobile is 7.1 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.)
1.69 A
Correct: Your answer is correct.
5.[2/2 Points] 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.
(a) What is the maximum total power that can be supplied by the outlets without blowing the
fuse?
2400 W
Correct: Your answer is correct.
(b) How many 1,600-W appliances can be plugged into the sockets without blowing the fuse?
1 appliance(s)
Correct: Your answer is correct.
6.[2/2 Points] 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.
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.
Correct: Your answer is correct.
7.[2/2 Points] During 42 seconds of use, 300 C of charge flow through a microwave oven.
Compute the size of the electric current.
7.143 A
Correct: Your answer is correct.
8.[2/2 Points] A lightning stroke lasts 0.03 s and involves a flow of 241 C. What is the current?
8033.33 A
Correct: Your answer is correct.
9.[2/2 Points] A current of 25.8 A flows through an electric heater operating on 120 V. What is
the heater's resistance?
4.65 Ω
Correct: Your answer is correct.
10.[2/2 Points] An electric eel can generate a 470-V, 0.8-A shock for stunning its prey. What is
the eel's power output?
376 W
Correct: Your answer is correct.
11.[2/2 Points] An electric train operates on 880 V. What is its power consumption when the
current flowing through the train's motor is 2,190 A?
1927200 W
Correct: Your answer is correct.
12.[2/2 Points] An electric clothes dryer is rated at 3,000 W. How much energy does it use in 35
min?
1.75 kWh
Correct: Your answer is correct.
13.[2/2 Points] Which costs more, running a 2,000-W hair dryer for 7 min or leaving a 80-W
lamp on overnight (10 h)?
the lamp
Correct: Your answer is correct.
14.[2/2 Points] The resistance of an electric heater is 90 Ω when connected to 120 V. How much
energy does it use during 40 min of operation?
384000J
Correct: Your answer is correct.
15.[2/2 Points] What would an audio speaker like that shown in the figure below do at the
instant a low-voltage battery is connected to it?
The speaker cone would either be pushed outward or pulled inward until the current stopped.
Correct: Your answer is correct.
16.[2/2 Points] The generator at a power plant produces AC at 20,000 V. A transformer steps
this up to 305,000 V for transmission over power lines. If there are 1,950 turns of wire in the
input coil of the transformer, how many turns must there be in the output coil?
Correct: Your answer is correct.
29737.5 turns
17.[2/2 Points] The blackbody radiation emitted from a furnace peaks at a wavelength of 4.2
10-6 m (0.0000042 m). What is the temperature inside the furnace?
690.476 K
Correct: Your answer is correct.
18.[2/2 Points] Which type of EM wave does your body emit most strongly?
Infrared.
Correct: Your answer is correct.
19.[2/2 Points] The charger cord used to recharge a cell phone contains a transformer that
reduces 120 V AC to 5 V AC. For each 1,350 turns in the input coil, how many turns are there in
the output coil? (Round your answer to at least one decimal place.)
56.25 turns
Correct: Your answer is correct.
20.[2/2 Points] Compute the frequency (in MHz) of an EM wave with a wavelength of 5.5 in.
(0.1397 m).
2147.5 MHz
Correct: Your answer is correct.
21.[2/2 Points] 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?
The magnet in the middle will remain motionless.
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.
22.[2/2 Points] Select all of the following descriptions that match what happens when a
ferromagnetic material is placed in an external magnetic field.
The external magnetic field induces magnetic poles in the ferromagnetic material.
The ferromagnetic material becomes magnetized.
Correct: Your answer is correct.
23.[2/2 Points] 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?
The magnetic field is perpendicular to the direction of the current.
Correct: Your answer is correct.
24.[3/3 Points] 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 motion of the motor induces an electric current, and the motor functions as a generator.
Correct: Your answer is correct.
