Physics Unit 3
How are motors and generators alike?
Both motors and generators use rotating armatures.
Four compasses are placed around a wire, as shown. The wire is then connected to a battery so that a current flows down the wire. How will the compasses point once the current is flowing?
C
The magnetic field 0.01 m from a wire carrying a current of 20 A is 0.004 T. The current in the wire and the distance from the wire are changed, as recorded in the table.
D
If a magnet is broken into two pieces, what happens to the magnetic poles?
Each piece will have a north pole and a south pole.
Which equation is used to calculate the magnetic force on a charge moving in a magnetic field?
F = |q|vBsin
How does the north pole of a magnet respond to the poles of other magnets?
It attracts the south pole and repels the north pole.
An iron nail does not pick up paper clips as a magnet would.
It has domains that are not aligned.
Which describes the magnetic field that forms when a wire carries an electric current?
It is in a cylinder around the wire.
What is the purpose of the metal core in an electromagnet?
It is magnetized by the field of the solenoid and increases the magnetic field strength.
Which statement describes the magnetic field inside a bar magnet?
It points from south to north.
The diagram shows a nail before and after a procedure was done. Which statement best explains what was likely done to the nail?
It was struck repeatedly, which caused the domains to randomize and the nail to become nonmagnetic.
A magnetically soft material is placed in a strong magnetic field.
It will become a temporary magnet because the domains will easily realign.
Which magnetic property best describes a magnet's ability to act at a distance?
Magnets have magnetic fields.
Which best describes what happens in an electric generator?
Motion causes constantly changing magnetic fields to induce electrical energy.
Craig is modeling the discovery of electromagnetism. Which procedure should he use?
NOT moving a magnet into a coil of wire in a closed-circuitg
Keiko builds a transformer in the lab, but it does not decrease the voltage as much as she needs. What should Keiko change to further reduce the voltage?
She should increase the number of coils in the primary winding.
What are step-down transformers used for?
Step-down transformers decrease the voltage that leaves a power plant.
How does an electric generator work?
The axle rotates the armature in the magnetic field of an electromagnet, which induces an electric current.
Which best describes the steps involved in the operation of an electric generator?
The electric current passes from the slip rings, through the brushes, and to the collection device.
Joan makes the device shown in her science class. What would happen to the magnetic field if she connects the battery in the opposite direction?
The field would reverse its poles.
Before beginning an experiment, Mrs. Wilson warns her science class not to drop the bar magnets on the floor. What is the most likely reason for Mrs. Wilson's warning?
The magnet might lose its magnetism.
Imagine the current in a current-carrying wire is flowing into the screen. What is the direction of the magnetic field around this current?
The magnetic field is clockwise.
Pedro uses a bar magnet to pick up a nail. He then touches the tip of the nail to some staples.
The nail has become a temporary magnet, while the bar magnet remains a permanent magnet.
How does an electric motor use magnetic force to produce motion
The north pole of an electromagnet placed in the center of a permanent magnet repels the north pole of the permanent magnet.
Which is true of a step-down transformer but not a step-up transformer?
The primary winding has more coils than the secondary winding.
Roberto plans to use two transformers to reduce a voltage of 120 V to 4 V. He uses a transformer that has 300 coils in the primary winding and 50 coils in the secondary winding. He has four other transformers, as listed in the table.
X
Which part of the motor is responsible for reversing the flow of current?
X
The table lists information about four devices. Which lists the devices in order from greatest magnetic field strength to weakest?
X,Y,Z,W
Elena makes a table to organize the functions of electric motor components.
X: Allows current to flow into the commutatorY: Conducts current to the armature and reverses direction of current
Which image represents a solenoid?
a
When the north pole of a bar magnet is moved into a solenoid, the needle on a galvanometer attached to the solenoid moves to the left, indicating that a current is produced. The magnet is then pulled out at a faster speed. What will be the result?
a larger current in the opposite direction
Which will produce a magnetic field?
a wire carrying a current
The magnetic field 0.02 m from a wire is 0.1 T. What is the magnitude of the magnetic field 0.01 m from the same wire?
0.2 T
Particle q1 has a charge of 2.7 μC and a velocity of 773 m/s. If it experiences a magnetic force of 5.75 × 10-3N, what is the strength of the magnetic field? In the same magnetic field, particle q2 has a charge of 42.0 μC and a velocity of 1.21 × 103 m/s. What is the magnitude of the magnetic force exerted on particle 2?
1) 2.8 2) 0.12
What is the force exerted on a moving charge of -2.0 μC at a 20° angle through a magnetic field of 3.0 × 10-4 T with a velocity of 5.0 × 106 m/s?
1.0 × 10-3 N
A point charge of 6.8 C moves at 6.5 × 104 m/s at an angle of 15° to a magnetic field that has a field strength of 1.4 T. What is the magnitude of the magnetic force acting on the charge?
1.6 × 10-1 N
Which statements best describe magnets? Check all that apply.
1245
Hiro wants to model the magnetic field of a bar magnet using a shoe box and pipe cleaners. He labels the ends of the shoe box N and S. How should he position the pipe cleaners? Check all that apply.
135
Which actions most likely cause the domains within a material to lose their alignment and become more randomized? Check all that apply.
146
A point charge of 5.0 × 10-7 C moves to the right at 2.6 × 105 m/s in a magnetic field that is directed into the screen and has a field strength of 1.8 × 10-2 T. What is the magnitude of the magnetic force acting on the charge?
2.3 × 10-3 N
Which diagram shows magnets aligned so they will attract each other?
3
Which is the correct representation of the right-hand rule for a current flowing to the right?
3
What is the force exerted on a charge of 2.5 µC moving perpendicular through a magnetic field of 3.0 × 102 T with a velocity of 5.0 × 103 m/s?
3.8 N
The voltage entering a transformer's primary winding is 120 volts. The primary winding is wrapped around the iron core 10 times. The secondary coil is wrapped around the core 4 times. What is the voltage leaving the transformer?
48
A point charge of 5.7 µC moves at 4.5 × 105 m/s in a magnetic field that has a field strength of 3.2 mT, as shown in the diagram.
6.6 × 10-3 N
Based on the diagram, the voltage at the secondary winding is V.
60
The voltage leaving the secondary coil of a transformer is equal to 240 V. The secondary coil is wrapped 8 times around the core. The primary coil is wrapped 25 times around the core. What is the initial voltage at the primary coil?
750
A force of 1.5 × 102 N is exerted on a charge of 1.4 × 10-7C that is traveling at an angle of 75° to a magnetic field. If the charge is moving at 1.3 × 106 m/s, what is the magnetic field strength?
8.5 × 102 T
A charged particle moves at 2.5 × 104 m/s at an angle of 25° to a magnetic field that has a field strength of 8.1 × 10-2 T.
8.8 × 10-5 C
Lidia makes a graphic organizer to compare temporary magnets with permanent magnets.
A
Four compasses are placed around a wire, as shown. What is the best conclusion that can be drawn?
A current does not flow in the wire.
Lionel explores electromagnetic induction using the procedure shown. 1. Move the magnet quickly into the right end of a solenoid.2. Hold the magnet in the solenoid for 3 s.3. Move the solenoid slowly to the left away from the magnet. What should Lionel observe during his investigation?
A large current forms, drops to zero, then a smaller current forms in the opposite direction.
Which of these situations would generate electrical current in a wire? Check all that apply.
abe
What must be known to determine the direction of the magnetic force on a charge? Check all that apply.
acd
Which device converts kinetic energy into electrical energy?
an electric generator
Which device converts electrical energy into kinetic energy?Which device converts kinetic energy into electrical energy?
an electric motor
In an electric motor, the rotating coil of wires wrapped around an iron core is a(n)
armaure
Look carefully at the diagrams and choose the one that represents a generator.
b
Which statements correctly describe the relationship between a solenoid and an electromagnet? Check all that apply.
bce
Which statements describe magnetic poles? Check all that apply.
bce
Which parts are found in motors? Check all that apply.
bcef
An electric current is produced using a bar magnet and a solenoid. Which changes will cause a decrease in the electric current produced? Check all that apply.
be
A charge is moving in a magnetic field that points to the left. What direction can the charge move and experience no magnetic force? Check all that apply.
cd
This diagram shows the magnetic field lines near the ends of two magnets. There is an error in the diagram.
changing the S to N
Trent builds a model electric motor. When he connects a battery to the motor, the motor spins through a half rotation and stops. Which is the most likely solution to the problem?
checking the commutator, because the current is not reversing
A wire has a current that flows to the right. Which describes the magnetic field produced by the current?
circles around the wire that go in at the bottom
Yoon Ki investigates electromagnetic induction by moving a bar magnet into a coil of wire. His experimental setup is shown. What change would most improve his results?
connecting the galvanometer to the coil
A cluster of atoms whose magnetic fields are aligned in the same direction is a magnetic .
domain
The generation of an electric current in a closed circuit by a changing magnetic field is
electromagnet induction
The generation of a magnetic field by an electric current is
electromagnetism
When using the right-hand rule to determine the direction of the magnetic force on a charge, which part of the hand points in the direction of the magnetic field?
fingers
Eva makes a graphic organizer to compare electromagnets with solenoids. Which description belongs in the region marked X?
has a metal core
Which change can make a generator stronger?
increasing the number of coils in the armature
A wire runs left to right and carries a current in the direction shown. What is the direction of the magnetic field at point Z?
into the screen
Steel objects can become temporary magnets because they are mainly composed of which element?
iron
According to the diagram, which way is the magnetic field pointing?
left
The diagram shows a negative charge moving in a magnetic field. In which direction is the magnetic force acting on the charge?
left
Tonya is modeling the discovery of electromagnetic induction. Which procedure should she use?
moving a magnet into a coil of wire in a closed circuit
Use the right-hand rule for magnetic force to determine the charge on the moving particle. This is a BLANK charge.
negative
In what way does a temporary magnet provide an advantage over a permanent magnet?
A temporary magnet allows the user to determine when it is magnetic
Two bar magnets are labeled A and B. The ends of each magnet are numbered 1 or 2, but the poles are not labeled. When A1 is brought near B1, the bars repel.
A1 and B1 are like poles, but there is not enough information to tell whether they are north poles or south poles.
Which is an important step in how an electric motor uses magnetic force to produce motion?
As the north pole of the electromagnet nears the south pole of the permanent magnet, the current reverses and the poles of the magnets then repel.
Trina makes a diagram to summarize how to use the right-hand rule to determine the direction of the magnetic force on each type of charge. Which labels belong in the regions marked X, Y, and Z?
B
The magnetic field lines of a bar magnet spread out from the
north end to the south end.
A positive charge moving up enters a magnetic field pointing out of the screen. What is the direction of the magnetic force on the charge?
not left not up
What is the direction of the force for a negative charge moving downward in a magnetic field pointing to the left?
out of screen
Which is the best procedure to make a permanent magnet?
placing a magnetically hard material in a strong magnetic field
The ends of a magnet where the force is strongest are magnetic fieldspolesdomainscurrents.
poles
What is the direction of the current flowing through the wire—left or right? The current flows to the BLANK
right
A coil of wire that carries an electric current is a(n) .
solenoid
When using the right-hand rule to determine the direction of the magnetic field around a current-carrying wire, the fingerspalmbackthumb of the right hand must point in the direction of the current.
thumb
A device that increases or decreases the voltage of alternating current is a(n) .
transformer
A wire perpendicular to the screen carries a current in the direction shown.What is the direction of the magnetic field at point Z?
up
The diagram shows a positive charge moving in a magnetic field. In which direction is the magnetic force acting on the charge?
up
Julia produces a 2 mA current by moving the south pole of a bar magnet into a solenoid. The solenoid contains 150 loops of wire. Which change should Julia make to generate a larger current?
using more loops of wire in the coil
Which change will cause an increase in the electric current produced through electromagnetic induction?
using more wire loops in the solenoid
Gazala makes the device shown in the diagram and uses it to pick up four paper clips on the point of the nail. What change would enable Gazala to pick up eight paper clips?
wrapping the wire around the nail more times
