Electromagnets and Solenoids

Question 1

Use the solenoid figure. Which end is the north pole, and what happens if the battery connections are reversed?

Accepted Answer

The right end is north, and reversing the current makes the left end north.

Answer

The left end is north, and reversing the current makes the right end north.

Answer

The right end is north, and reversing the current leaves it north.

Answer

Neither end is north because a coil has no poles while current flows.

Question 2

Use the solenoid figure. Which end is the north pole while the current flows?

Accepted Answer

The left end is the north pole.

Answer

The right end is the north pole.

Answer

Both ends are north poles.

Answer

The coil has no magnetic poles because it is not a permanent magnet.

Question 3

In the solenoid figure, the current direction through the turns is shown. If the same current is sent through an oppositely wound coil, which pole change occurs?

Accepted Answer

The right end is north now, but the opposite winding would make the left end north.

Answer

The left end is north now, and the opposite winding would leave it north.

Answer

The right end is north now, and the opposite winding would switch the magnet off.

Answer

Both ends are north now, but the opposite winding would make both ends south.

Question 4

Use the solenoid figure. A soft iron core is inserted without changing the current. Which statement correctly names the north end?

Accepted Answer

The left end is north; the core strengthens the field but does not choose the pole direction.

Answer

The right end is north; the core always makes the battery-positive end north.

Answer

The left end is north; the core weakens the field by absorbing magnetism.

Answer

The right end is north; a solenoid cannot have poles until the core is steel.

Question 5

Use the field-line figure. If the magnetic field inside the solenoid points along the axis as shown, which end is the north pole?

Accepted Answer

The right end, because the internal field points toward the solenoid's north pole.

Answer

The left end, because magnetic field lines always enter a north pole.

Answer

The right end, because a current-carrying coil has only one pole.

Answer

The left end, because the battery direction does not affect pole direction.

Question 6

A student applies the right-hand rule to the current shown in the solenoid figure. What should the student identify?

Accepted Answer

The left end is north and the right end is south.

Answer

The right end is north and the left end is south.

Answer

Both ends are south because the current enters the page.

Answer

The poles alternate at every turn instead of forming end poles.

Question 7

Use the solenoid figure. A compass is placed just beyond the right end. Which description is consistent with the pole at that end?

Accepted Answer

The right end is north, so the compass north-seeking tip points away from it.

Answer

The right end is south, so the compass north-seeking tip points away from it.

Answer

The right end is north, so the compass has no torque near it.

Answer

The right end is south, so the compass south-seeking tip points toward it.

Question 8

Use the solenoid figure. What happens to the labeled pole behavior when the current is switched off in a soft iron-core electromagnet?

Accepted Answer

The left end is north while current flows, but the soft iron loses most magnetization when current stops.

Answer

The right end is north while current flows, and soft iron stays strongly magnetized forever.

Answer

The left end is north only after current stops, because the core is the source of the field.

Answer

The right end is north while current flows, but reversing the switch makes both ends south.

Question 9

Use the circuit figure. The coils have the same length and soft iron cores. Which coil is the stronger electromagnet?

Accepted Answer

Coil B, because it has more turns with the same current and length.

Answer

Coil A, because fewer turns leave more space for the magnetic field.

Answer

They are equally strong because the battery voltage is the same.

Answer

Coil A, because a shorter wire path always makes a stronger magnet.

Question 10

Use the circuit figure. The coils have the same number of turns, length, and soft iron core. Which one lifts more paperclips?

Accepted Answer

Coil A, because its current is larger.

Answer

Coil B, because its smaller current is used up less slowly.

Answer

They are equally strong because the coils have the same turns.

Answer

Coil B, because lower current makes the domains align better.

Question 11

Use the circuit figure. Both coils have the same current, number of turns, and length. Which coil is stronger?

Accepted Answer

Coil A, because a soft iron core concentrates and strengthens the field.

Answer

Coil B, because a wooden core lets the field pass without resistance.

Answer

They are equally strong because their currents and turns match.

Answer

Coil B, because the core material cannot affect an electromagnet.

Question 12

Use the circuit figure. The coils have the same turns, current, and core material but different winding lengths. Which coil has the stronger field inside?

Accepted Answer

Coil B, because the same turns are packed into a shorter length.

Answer

Coil A, because a longer coil has more wire touching the core.

Answer

They are equal because they have the same total number of turns.

Answer

Coil A, because stretching the turns spreads the field farther.

Question 13

Use the circuit figure. For these soft iron solenoids, compare I times turns per unit length. Which coil is stronger?

Accepted Answer

Coil A is stronger because 40 turns at 3.0 A over 10 cm gives the larger product.

Answer

Coil B is stronger because 80 total turns always wins.

Answer

They are equal because doubling turns cancels tripling current.

Answer

Coil B is stronger because a smaller current keeps the core cooler.

Question 14

Use the circuit figure. Both coils carry 1.0 A and have soft iron cores. Which solenoid has the larger field?

Accepted Answer

Coil B, because it has the greater number of turns per centimeter.

Answer

Coil A, because it has more total turns.

Answer

They are equal because their currents are equal.

Answer

Coil A, because a longer winding always gives a stronger field.

Question 15

What physical fact allows a current-carrying coil to act like a magnet?

Accepted Answer

Moving electric charges produce magnetic fields.

Answer

Stationary electric charges produce north poles only.

Answer

Insulated copper becomes ferromagnetic when bent into a circle.

Answer

A battery stores magnetic field lines that flow through the wire.

Question 16

A student keeps the same battery and core but rewinds the wire into more turns over the same length. What happens to the electromagnet?

Accepted Answer

It becomes stronger because the turns per unit length increase.

Answer

It becomes weaker because current is used up by each turn.

Answer

Its poles reverse because any extra turn changes north into south.

Answer

It switches off because the core blocks fields from many turns.

Question 17

Why is soft iron usually preferred to steel for an electromagnet core in a switchable device?

Accepted Answer

Soft iron magnetizes strongly and loses most magnetization when current stops.

Answer

Soft iron is nonmagnetic, so it prevents the coil from sticking.

Answer

Steel loses magnetization faster than soft iron after the switch opens.

Answer

Steel reverses the current direction inside the coil.

Question 18

A solenoid's battery leads are swapped while the coil and core stay the same. What changes?

Accepted Answer

The north and south poles reverse ends.

Answer

The electromagnet switches off even though the circuit is still closed.

Answer

The magnetic field becomes electric instead of magnetic.

Answer

The core becomes permanently magnetized in the original direction.

Question 19

A coil is rewound in the opposite direction, and the battery is also reversed. Compared with the original coil, what happens to the pole direction?

Accepted Answer

The poles stay the same because the two reversals cancel.

Answer

The poles reverse because any battery reversal always changes them.

Answer

The electromagnet switches off because opposite winding blocks current.

Answer

Both ends become north poles because the core is magnetized twice.

Question 20

A resistor is added in series with a solenoid connected to the same battery. What is the most likely effect on the electromagnet?

Accepted Answer

It becomes weaker because the current in the coil decreases.

Answer

It becomes stronger because resistance creates magnetic domains.

Answer

Its poles reverse because resistors reverse conventional current.

Answer

It becomes unchanged because only voltage, not current, affects a coil.

Question 21

A coil has 80 turns carrying 2.0 A. If the same 80 turns are spread over twice the original length, what happens to the field near the center?

Accepted Answer

It becomes weaker because the turns per unit length are smaller.

Answer

It becomes stronger because the longer wire makes a longer magnet.

Answer

It stays the same because only the total number of turns matters.

Answer

It reverses direction because the coil length changed.

Question 22

Why should the wire in a strong classroom electromagnet be insulated?

Accepted Answer

Insulation keeps current in the coil turns instead of shorting through touching wire or the core.

Answer

Insulation is the ferromagnetic material that creates the field.

Answer

Insulation reverses the poles every time the switch is opened.

Answer

Insulation uses up current so the core does not overheat magnetically.

Question 23

Which statement best describes the role of the soft iron core in an electromagnet?

Accepted Answer

The current creates the magnetic field, and the core's domains align to strengthen it.

Answer

The core creates the field first, and the current only heats the wire.

Answer

The core supplies electric charge that flows around the turns.

Answer

The core cancels the coil's field so only permanent magnetism remains.

Question 24

A powered solenoid loses its iron core but the same current still flows in the wire. What is true?

Accepted Answer

The coil still has a magnetic field, but it is weaker.

Answer

The coil has no magnetic field because only iron can create one.

Answer

The coil's poles reverse because the core was removed.

Answer

The coil becomes a permanent magnet with unchanged strength.

Question 25

A solenoid has a soft iron core. Which change would definitely make it a stronger electromagnet?

Accepted Answer

Increasing the current through the turns.

Answer

Using thicker wire while keeping the current the same.

Answer

Replacing the soft iron core with plastic.

Answer

Spreading the same turns over a longer length.

Question 26

A compass needle deflects when it is placed near a wire connected to a battery. What explains the deflection?

Accepted Answer

The electric current in the wire produces a magnetic field around the wire.

Answer

The battery's chemical energy pushes directly on the compass glass.

Answer

The compass uses up current as it points north.

Answer

The wire becomes a permanent magnet only after the current stops.

Question 27

A scrapyard crane lifts a steel car body and then drops it by opening a switch. Why use an electromagnet instead of a permanent magnet?

Accepted Answer

Its magnetism can be switched off to release the load.

Answer

It attracts aluminum more strongly than steel.

Answer

It becomes weightless when current flows.

Answer

It works only because current is used up in the steel.

Question 28

In an electromagnetic relay, what does the electromagnet do?

Accepted Answer

It pulls an armature to open or close a separate circuit.

Answer

It stores charge so the battery voltage becomes zero.

Answer

It turns a permanent magnet into an insulator.

Answer

It converts sound waves directly into light.

Question 29

In a simple electric bell, why does the hammer repeatedly strike the bell?

Accepted Answer

An electromagnet attracts an armature, which breaks and remakes the circuit.

Answer

A permanent magnet heats the bell until it vibrates.

Answer

A battery reverses Earth's magnetic field at the bell.

Answer

The bell stores current and releases it as sound.

Question 30

What is the role of the voice coil in a moving-coil loudspeaker?

Accepted Answer

Changing current in the coil makes it push and pull on the cone to create sound.

Answer

The coil stores sound waves before releasing them through the magnet.

Answer

The coil prevents any magnetic force from reaching the cone.

Answer

A steady current in the coil keeps the cone motionless while sound forms.

Question 31

Why does an MRI scanner use a large electromagnet or superconducting solenoid?

Accepted Answer

It produces a strong magnetic field used to align spins in body tissue.

Answer

It produces X-rays by heating a steel core.

Answer

It cancels all electric fields so the patient becomes weightless.

Answer

It attracts blood cells to the wall of the room.

Question 32

A magnetic door lock holds a steel plate when powered but releases when power is cut. What part of the lock is being used?

Accepted Answer

A switchable electromagnet attracting a steel armature plate.

Answer

A permanent magnet that becomes stronger when unplugged.

Answer

A plastic core that stores electric charge mechanically.

Answer

A generator coil that turns door motion into heat.

Question 33

In a maglev track, what do electromagnetic forces help do?

Accepted Answer

Levitate, guide, or propel the train without wheel-rail contact.

Answer

Increase friction so the wheels grip the rails more strongly.

Answer

Turn the train's steel body into a chemical battery.

Answer

Remove the need for any magnetic field around the train.

Question 34

A recycling conveyor needs to pull steel cans out of mixed waste and then let them drop into a bin. Which device best fits that job?

Accepted Answer

An electromagnet that can be energized over the belt and switched off over the bin.

Answer

A large permanent magnet fixed over both the belt and the bin.

Answer

A charged plastic plate that attracts the cans by static electricity.

Answer

An electromagnet that is switched on only while it is over the bin.

Question 35

A 200-turn solenoid is rewound to 400 turns over the same length and carries the same current. How does the magnetic field compare?

Accepted Answer

It is 2 times as large.

Answer

It is 1/2 as large.

Answer

It is 4 times as large.

Answer

It is unchanged.

Question 36

A solenoid's current increases from 1.5 A to 3.0 A while its turns and length stay the same. What happens to the field inside?

Accepted Answer

It doubles.

Answer

It is cut in half.

Answer

It quadruples.

Answer

It stays the same because the number of turns did not change.

Question 37

A solenoid has 300 turns over 15 cm. It is rewound to 300 turns over 5.0 cm with the same current. How does the field change?

Accepted Answer

It becomes 3 times as large.

Answer

It becomes 1/3 as large.

Answer

It becomes 9 times as large.

Answer

It stays unchanged because there are still 300 turns.

Question 38

Solenoid A has 250 turns over 10 cm at 1.2 A. Solenoid B has 500 turns over 20 cm at 1.2 A. Which field is larger?

Accepted Answer

They are equal because the turns per centimeter and current are the same.

Answer

A is larger because its turns are packed into the shorter total length.

Answer

B is larger because it has twice as many total turns.

Answer

B is larger because doubling length doubles the field.

Question 39

A solenoid has 120 turns over 12 cm at 2.0 A. A new one has 180 turns over 12 cm at 4.0 A. How strong is the new field compared with the original?

Accepted Answer

3 times as large.

Answer

1.5 times as large.

Answer

2 times as large.

Answer

6 times as large.

Question 40

A solenoid changes from 60 turns over 6.0 cm at 2.0 A to 60 turns over 12 cm at 3.0 A. What is the new field compared with the original?

Accepted Answer

3/4 as large.

Answer

3/2 as large.

Answer

2/3 as large.

Answer

3 times as large.

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Electromagnets and Solenoids

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Top Corner

Electromagnets and Solenoids

Ways to Play

Device Games: Students play on their phones

Blast Go

Zombie Escape

Avalanche

Maze Blast

Cave Climb

Blast Out

Mystery Auction

Tour Guide

Food Truck Rush

Tug of War

Alien Blast

Glacier Rush

Board Games: Teacher-led, projected to the class

Like what you see?

More like this

Bug Blast

BlastRace

BlastQuiz

BlastBoard

Seek & Destroy

Mystery Blast

Checkers

Texas Hold 'Em

Da Bomb

Castle Siege

Hot Potato

Market Mayhem

King of the Hill

Bank Heist

Top Corner