Unit Test — Unit test Answers

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A circuit has a current of 1.2 A. If the voltage decreases to one-third of its original amount while the resistance remains constant, what will be the resulting current?

A
0.3 A
B
0.4 A
C
1.2 A
D
3.6 A
2
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Selena drew a diagram to show how current moves in a loop of wire that is placed between two magnets.

Question illustration
A
She can change the magnets so like poles are facing each other.
B
She can change the arrows so they show current traveling in opposite directions on the sides of the loop.
C
She can change the arrows so they show the magnetic field reversing direction between the magnets.
D
She can change the magnetic poles so they are both on one side of the loop.
3

Dr. Eriksson is working on a material called selenium. She is adding a certain number and type of atoms to the selenium, which will control its conductivity.

A
semiconductor
B
conductor
C
superconductor
D
insulator
4

Which best compares a brush and a commutator in an electric motor?

A
Both rotate when the motor is on.
B
Both carry electrical current from a power source.
C
Both remain stationary when the motor is on.
D
Both have a permanent magnetic field.
5

What does voltage describe?

A
how fast current can flow
B
how much current can flow
C
how much a material resists electrical flow
D
how fast a material conducts electrical flow
6

Which best contrasts an electric generator and an electric motor?

A
In a generator, slip rings function as a solenoid, and in a motor, an armature functions as a solenoid.
B
In a motor, slip rings function as a solenoid, and in a generator, an armature functions as a solenoid.
C
A generator converts electrical energy to kinetic energy, and a motor converts kinetic energy to electrical energy.
D
A generator converts kinetic energy to electrical energy, and a motor converts electrical energy to kinetic energy.
7

How are the electric field lines around a positive charge affected when a second positive charge is near it?

A
The field lines combine with the lines around the second positive charge.
B
The field lines overlap with the lines from the second positive charge.
C
The field lines bend toward the second positive charge.
D
The field lines bend away from the second positive charge.
8

Oran wants to model the behavior of Earth’s magnetic field when Earth’s magnetic south is near Earth’s geographic north using a ball, a bar magnet, and a compass. He designates the top of the ball as Earth’s geographic north.

Question illustration
A
Model 1
B
Model 2
C
Model 3
D
Model 4
9

Which current is produced in homes?

A
magnetic
B
voltage
C
alternating
D
direct
10

Badri makes the table below to review the factors that affect the electric force between objects.

Question illustration
A
changing “Direct” to “Indirect”
B
changing “Indirect” to “Direct”
C
changing “Distance” to “Amount of electric charge”
D
changing “Mass” to “Amount of electric charge”
11

What must be true in order for magnetism to induce an electric current in a wire?

A
There needs to be a switch in the circuit.
B
There cannot be a switch in the circuit.
C
The wire must be part of a closed circuit.
D
The wire must be part of an open circuit.
12

A component of a circuit changes, as shown below.

Question illustration
A
A switch is closed, so the circuit would be incomplete and broken and the lights in the circuit would not shine.
B
A switch is closed, so the circuit would be complete and unbroken and the lights in the circuit would shine.
C
A switch is opened, so the circuit would be incomplete and broken and the lights in the circuit would not shine.
D
A switch is opened, so the circuit would be complete and unbroken and the lights in the circuit would shine.
13

Liang is working with an electrical circuit. She replaces a straight electrical wire with a coiled wire.

A
increase the strength of the magnetic field when current flows through the circuit
B
decrease the strength of the magnetic field when current flows through the circuit
C
increase the current that flows through the wire when the circuit is active
D
decrease the current that flows through the wire when the circuit is active
14

Horatio drew a diagram to illustrate how magnetism is produced by electric currents.

Question illustration
A
Magnetism is not produced by electric currents unless the wire is coiled.
B
The magnetic field does not continually spread outward from the wire.
C
The magnetic field is produced inside the wire, not outside of it.
D
Magnetism is only produced when a metal bar is placed near the wire.
15

Two bar magnets are held close together. When they are released, they move toward one another. Which best describes the original placement of the magnets?

A
The magnets are placed end to end with the north pole of each pointing toward the other.
B
The magnets are placed end to end with the south pole of each pointing toward the other.
C
The magnets are placed side by side with the like poles of each magnet near the other.
D
The magnets are placed side by side with the opposite poles of each magnet near the other.
16

Based on illustrations of magnetic field lines, where could an object be placed so it would not experience a magnetic force?

A
halfway between the like poles of two magnets, because the field lines bend away and do not enter this area
B
halfway between the opposite poles of two magnets, because the field lines are the closest together
C
above the middle of a bar magnet, because the magnetic field lines are only found around the sides of the magnet
D
above a pole of a bar magnet, because the magnetic field lines either go in or go out at the end
17

Which unit is used to measure resistance?

A
volts
B
charges
C
amperes
D
ohms
18

Look at the circuit diagram.

Question illustration
A
one
B
two
C
three
D
four
19

A positively charged object is placed to the left of a negatively charged object. Which best describes how the positively charged object will move?

A
to the left, in the direction of the electric field lines
B
to the right, in the direction of the electric field lines
C
up in the direction that the field lines bend away
D
down in the direction that the field lines bend away
20

The diagram shows two charged objects, A and B.

Question illustration
A
A: positiveB: negative
B
A: negativeB: positive
C
A: negativeB: negative
D
A: positiveB: positive

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