A solenoid is a wire wound into a coil, which increases the strength of the magnetic field produced compared to a single wire, producing a field similar to that of a bar magnet .

What is the shape of the magnetic field pattern around a straight current-carrying wire?

Concentric circles centred on the wire, showing that the field around a current-carrying wire has no poles .

How does the strength of the magnetic field around a wire change with distance from the wire?

The field is strongest closest to the wire and gets weaker as the distance from the wire increases.

Reversing the direction of the current flowing through a wire will ______ the direction of the magnetic field around it.

Reversing the direction of the current flowing through a wire will reverse the direction of the magnetic field around it.

Give three ways the strength of the magnetic field produced by a solenoid can be increased.

Increasing the current ; increasing the number of turns in the coil for a given length; adding an iron core through the centre of the coil.

Define an electromagnet .

An electromagnet is a solenoid with an iron core , whose magnetic field can be switched on and off by turning the current on and off.

True or False? A solenoid with no current flowing through it still produces a magnetic field.

False. If there is no current flowing through the wire, there is no magnetic field produced around or through the solenoid.

How can you determine which end of a solenoid is the north pole and which is the south pole?

View the solenoid from the end. If the current travels clockwise , that end is the south pole . If the current travels anticlockwise , that end is the north pole .

Define the motor effect .

The motor effect occurs when a wire carrying a current is placed in a magnetic field and experiences a force , as a result of the two magnetic fields interacting.

Give three ways to increase the force experienced by a current-carrying wire in a magnetic field.

Increasing the current flowing through the wire; using stronger magnets ; placing the wire at 90° to the magnetic field lines.

The motor effect is a result of ______ interacting magnetic fields producing a force on a wire.

The motor effect is a result of two interacting magnetic fields producing a force on a wire.

True or False? The force on a current-carrying wire in a magnetic field is zero when the wire is parallel to the field.

True. When the two magnetic fields are parallel , there is no interaction between them, so no force is produced.

Define magnetic flux density .

Magnetic flux density , B , is the strength of a magnetic field, measured in tesla (T) .

Define Fleming's left-hand rule .

Fleming's left-hand rule is used to find the direction of the force (thrust) on a current-carrying wire in a magnetic field: the F irst finger points in the direction of the F ield, the se C ond finger points in the direction of the C urrent, and the TH umb points in the direction of the TH rust (force).

In Fleming's left-hand rule, what direction does the First finger point in?

The direction of the magnetic field .

In Fleming's left-hand rule, what direction does the thumb point in?

The direction of the force (thrust) acting on the wire.

The directions of the current, magnetic field and force in Fleming's left-hand rule are all ______ to each other.

The directions of the current, magnetic field and force in Fleming's left-hand rule are all perpendicular to each other.

True or False? Fleming's left-hand rule gives the direction of the current flowing through a wire.

False. Fleming's left-hand rule gives the direction of the force on the wire, using the already-known directions of the current and the magnetic field.

Define a split-ring commutator .

A split-ring commutator is a circular tube of metal split in two, attached to the coil of a d.c. motor, which reverses the direction of the current through the coil every half turn so the coil continues to rotate in the same direction.

What is the function of the carbon brushes in a d.c. motor?

They maintain contact between the split ring and the rest of the circuit, allowing current to flow into the rotating coil.

What happens to the current and the force acting on the coil of a d.c. motor once it has rotated to the vertical position?

The split ring is no longer in contact with the brushes, so no current flows and no force acts on the coil.

The split ring reverses the direction of the current through the coil every ______ turn, so the coil continues to rotate in the same direction.

The split ring reverses the direction of the current through the coil every half turn, so the coil continues to rotate in the same direction.

Give two ways to increase the speed at which the coil of a d.c. motor rotates.

Increasing the current ; using a stronger magnet .

Give two ways to change the direction of rotation of a d.c. motor.

Reversing the direction of the current supply ; reversing the direction of the magnetic field by reversing the poles of the magnet.

Give three ways to increase the force supplied by a d.c. motor.

Increasing the current in the coil; increasing the strength of the magnetic field ; adding more turns to the coil.

True or False? The carbon brushes in a d.c. motor are attached directly to the coil and rotate with it.

False. The carbon brushes stay in contact with the split ring , which is attached to the coil; the brushes themselves do not rotate.

Define a loudspeaker .

A loudspeaker converts electrical signals into sound. It consists of a coil of wire wrapped around one pole of a permanent magnet , and works due to the motor effect .

How are headphones related to loudspeakers?

Headphones are essentially small moving-coil loudspeakers, and work in exactly the same way.

In a loudspeaker, what is the coil of wire wrapped around?

One pole of a permanent magnet .

Why does the force on the coil of a loudspeaker constantly change direction?

Because the current is constantly changing direction, the magnetic field produced around the coil is also constantly changing direction , so the force on it constantly changes direction too.

The oscillating coil of a loudspeaker causes the speaker ______ to oscillate, which makes the air oscillate and creates sound waves.

The oscillating coil of a loudspeaker causes the speaker cone to oscillate, which makes the air oscillate and creates sound waves.

True or False? A loudspeaker uses direct current to make its coil oscillate.

False. A loudspeaker uses alternating current , which constantly changes direction, to make the coil oscillate.

GCSEPhysicsAQAFlashcardsMagnetism & ElectromagnetismThe Motor Effect

The Motor Effect (AQA GCSE Physics): Flashcards

Exam code: 8463

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FrontMagnetic Fields in Wires & Solenoids
Define a solenoid.

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Cards in this collection (37)

Define a solenoid.
A solenoid is a wire wound into a coil, which increases the strength of the magnetic field produced compared to a single wire, producing a field similar to that of a bar magnet.
What is the shape of the magnetic field pattern around a straight current-carrying wire?
Concentric circles centred on the wire, showing that the field around a current-carrying wire has no poles.
How does the strength of the magnetic field around a wire change with distance from the wire?
The field is strongest closest to the wire and gets weaker as the distance from the wire increases.
Which rule is used to work out the direction of the magnetic field around a current-carrying wire?
The right-hand thumb rule.
Reversing the direction of the current flowing through a wire will ______ the direction of the magnetic field around it.
Reversing the direction of the current flowing through a wire will reverse the direction of the magnetic field around it.
Give three ways the strength of the magnetic field produced by a solenoid can be increased.
Increasing the current; increasing the number of turns in the coil for a given length; adding an iron core through the centre of the coil.
Define an electromagnet.
An electromagnet is a solenoid with an iron core, whose magnetic field can be switched on and off by turning the current on and off.
True or False?
A solenoid with no current flowing through it still produces a magnetic field.
False.
If there is no current flowing through the wire, there is no magnetic field produced around or through the solenoid.
How can you determine which end of a solenoid is the north pole and which is the south pole?
View the solenoid from the end. If the current travels clockwise, that end is the south pole. If the current travels anticlockwise, that end is the north pole.
Define the motor effect.
The motor effect occurs when a wire carrying a current is placed in a magnetic field and experiences a force, as a result of the two magnetic fields interacting.
Give three ways to increase the force experienced by a current-carrying wire in a magnetic field.
Increasing the current flowing through the wire; using stronger magnets; placing the wire at 90° to the magnetic field lines.
The motor effect is a result of ______ interacting magnetic fields producing a force on a wire.
The motor effect is a result of two interacting magnetic fields producing a force on a wire.
True or False?
The force on a current-carrying wire in a magnetic field is zero when the wire is parallel to the field.
True.
When the two magnetic fields are parallel, there is no interaction between them, so no force is produced.
Define magnetic flux density.
Magnetic flux density, B, is the strength of a magnetic field, measured in tesla (T).
State the equation used to calculate the force on a current-carrying conductor in a magnetic field, including the unit of each quantity.
$F = B I L$
F = force in newtons (N); B = magnetic flux density in tesla (T); I = current in amps (A); L = length of conductor in the magnetic field in metres (m).
A 0.05 m length of wire at right angles to a magnetic field carries a current of 1.5 A and experiences a force of 0.06 N. Calculate the magnetic flux density of the field.
$B = \frac{F}{I L} = \frac{0.06}{1.5 \times 0.05}$
*B* = 0.8 T
Define Fleming's left-hand rule.
Fleming's left-hand rule is used to find the direction of the force (thrust) on a current-carrying wire in a magnetic field: the First finger points in the direction of the Field, the seCond finger points in the direction of the Current, and the THumb points in the direction of the THrust (force).
In Fleming's left-hand rule, what direction does the First finger point in?
The direction of the magnetic field.
In Fleming's left-hand rule, what direction does the thumb point in?
The direction of the force (thrust) acting on the wire.
The directions of the current, magnetic field and force in Fleming's left-hand rule are all ______ to each other.
The directions of the current, magnetic field and force in Fleming's left-hand rule are all perpendicular to each other.
True or False?
Fleming's left-hand rule gives the direction of the current flowing through a wire.
False.
Fleming's left-hand rule gives the direction of the force on the wire, using the already-known directions of the current and the magnetic field.
A current-carrying wire is placed horizontally between the poles of a magnet, with the field and current directions as shown in a worked example. Using Fleming's left-hand rule, in which direction does the wire experience a force?
Downwards.
Define a split-ring commutator.
A split-ring commutator is a circular tube of metal split in two, attached to the coil of a d.c. motor, which reverses the direction of the current through the coil every half turn so the coil continues to rotate in the same direction.
What is the function of the carbon brushes in a d.c. motor?
They maintain contact between the split ring and the rest of the circuit, allowing current to flow into the rotating coil.
What happens to the current and the force acting on the coil of a d.c. motor once it has rotated to the vertical position?
The split ring is no longer in contact with the brushes, so no current flows and no force acts on the coil.
The split ring reverses the direction of the current through the coil every ______ turn, so the coil continues to rotate in the same direction.
The split ring reverses the direction of the current through the coil every half turn, so the coil continues to rotate in the same direction.
Give two ways to increase the speed at which the coil of a d.c. motor rotates.
Increasing the current; using a stronger magnet.
Give two ways to change the direction of rotation of a d.c. motor.
Reversing the direction of the current supply; reversing the direction of the magnetic field by reversing the poles of the magnet.
Give three ways to increase the force supplied by a d.c. motor.
Increasing the current in the coil; increasing the strength of the magnetic field; adding more turns to the coil.
True or False?
The carbon brushes in a d.c. motor are attached directly to the coil and rotate with it.
False.
The carbon brushes stay in contact with the split ring, which is attached to the coil; the brushes themselves do not rotate.
Define a loudspeaker.
A loudspeaker converts electrical signals into sound. It consists of a coil of wire wrapped around one pole of a permanent magnet, and works due to the motor effect.
How are headphones related to loudspeakers?
Headphones are essentially small moving-coil loudspeakers, and work in exactly the same way.
In a loudspeaker, what is the coil of wire wrapped around?
One pole of a permanent magnet.
Why does the force on the coil of a loudspeaker constantly change direction?
Because the current is constantly changing direction, the magnetic field produced around the coil is also constantly changing direction, so the force on it constantly changes direction too.
The oscillating coil of a loudspeaker causes the speaker ______ to oscillate, which makes the air oscillate and creates sound waves.
The oscillating coil of a loudspeaker causes the speaker cone to oscillate, which makes the air oscillate and creates sound waves.
True or False?
A loudspeaker uses direct current to make its coil oscillate.
False.
A loudspeaker uses alternating current, which constantly changes direction, to make the coil oscillate.
Which rule can be used to determine the direction of the force on the coil of a loudspeaker at any instant?
Fleming's left-hand rule.

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