What happens around a conducting wire when a current flows through it?

A magnetic field is produced around the wire.

Define magnetic field lines around a current-carrying wire.

Concentric circles centred on the wire, showing that the field has no poles .

How can the shape and direction of the magnetic field around a wire be investigated?

Using plotting compasses placed around the wire.

Reversing the direction in which the current flows through the wire will ______ the direction of the magnetic field.

Reversing the direction in which the current flows through the wire will reverse the direction of the magnetic field.

What two factors does the strength of the magnetic field around a wire depend on?

The size of the current and the distance from the conductor.

True or False? Field lines around a current-carrying wire get closer together as the current increases.

True. A larger current produces a stronger magnetic field, shown by field lines becoming more closely spaced.

A wire looped into a coil , which increases the strength of the magnetic field compared to a single wire.

What is the magnetic field like inside a solenoid?

Strong and uniform , running along the centre of the solenoid.

Why is the field inside a solenoid strong while the field outside it is weak?

Inside, the fields from individual coils add together ; outside, they cancel .

The strength of the magnetic field around a solenoid can be increased by increasing the current, increasing the ______ in the coil, or adding an ______ .

The strength of the magnetic field around a solenoid can be increased by increasing the current, increasing the number of turns in the coil, or adding an iron core .

Why does adding an iron core through a solenoid increase its overall magnetic strength?

The iron core becomes an induced magnet when current flows, and its field combines with the solenoid's field to create a much stronger magnet.

True or False? The individual loops of a coil should be called "more coils" rather than "turns".

False. The coil describes the overall object; the individual loops should be called turns , so the correct phrase is "add more turns to the coil".

Define the motor effect .

When a wire with current flowing through it is placed in a magnetic field and experiences a force .

What causes the force on a current-carrying wire in the motor effect?

The interaction of two magnetic fields : the field around the wire due to its current, and the external field it is placed in.

Name two ways to increase the force on a current-carrying wire in a magnetic field.

Increase the current , use a stronger magnet , or place the wire at 90° to the field.

At what angle to the magnetic field should a current-carrying wire be placed to produce the maximum force ?

90° to the magnetic field lines.

If the two magnetic fields are ______ , there will be no interaction between them and therefore ______ .

If the two magnetic fields are parallel , there will be no interaction between them and therefore no force produced .

True or False? Using a weaker magnet increases the force on a current-carrying wire.

False. Stronger magnetic fields produce stronger forces, so a weaker magnet would decrease the force.

What three quantities does Fleming's left-hand rule relate?

The directions of the force (thrust), the magnetic field , and the current .

How are the force, field and current directions arranged relative to each other in Fleming's left-hand rule?

They are all perpendicular to each other.

Define what each finger and thumb represent in Fleming's left-hand rule .

F irst finger = F ield, se C ond finger = C urrent, TH umb = TH rust (force).

The magnetic field is always in the direction from ______ to ______ , and current is always in the direction of a positive terminal to a negative terminal.

The magnetic field is always in the direction from North to South , and current is always in the direction of a positive terminal to a negative terminal.

True or False? The force on a current-carrying wire in a magnetic field can only ever act left or right in the plane of the page.

False. Because the force, field and current are all perpendicular to each other, the force can act into or out of the page as well.

Define magnetic flux density , B .

The strength of a magnetic field, measured in tesla (T) .

In the equation F = BIL , what do I and L represent?

I is the current through the conductor (A); L is the length of conductor in the magnetic field (m).

In F = BIL , F is measured in ______ , B in ______ , and L in metres.

In F = BIL , F is measured in newtons , B in tesla , and L in metres.

True or False? You may be asked to calculate the force on a wire at any angle to the magnetic field.

False. You will only be expected to calculate the force when the wire is perpendicular (90°) to the field.

What are the two key components that connect the rotating coil of a d.c. motor to the circuit?

A split ring and carbon brushes .

Why do the two sides of a current-carrying coil in a d.c. motor experience forces in opposite directions ?

Current flows in opposite directions along each side of the coil, so Fleming's left-hand rule gives forces in opposite directions, causing rotation.

Why does the coil in a d.c. motor keep rotating when it passes through the vertical position, even though no force acts on it there?

The momentum of the coil carries it past the vertical position until the split ring reconnects with the brushes.

Define split-ring commutator .

A circular tube of metal split in two, connected to the coil, which reverses the connection to the circuit every half rotation so the coil keeps turning in the same direction.

The direction of rotation of the coil in a d.c. motor can be changed by reversing the direction of the current supply, or by reversing the ______ of the magnet.

The direction of rotation of the coil in a d.c. motor can be changed by reversing the direction of the current supply, or by reversing the poles of the magnet.

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

Increase the current in the coil, increase the strength of the magnetic field , or add more turns to the coil.

True or False? When the coil of a d.c. motor is vertical, current still flows through it and a force still acts on it.

False. When vertical, the split ring is not in contact with the brushes, so no current flows and no force acts .

GCSEPhysicsEdexcelFlashcards12. Magnetism & the Motor EffectElectromagnetism & The Motor Effect

Electromagnetism & The Motor Effect (Edexcel GCSE Physics): Flashcards

Exam code: 1PH0

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FrontMagnetic Fields in Wires
What happens around a conducting wire when a current flows through it?

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Cards in this collection (38)

What happens around a conducting wire when a current flows through it?
A magnetic field is produced around the wire.
Define magnetic field lines around a current-carrying wire.
Concentric circles centred on the wire, showing that the field has no poles.
How can the shape and direction of the magnetic field around a wire be investigated?
Using plotting compasses placed around the wire.
What 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 in which the current flows through the wire will ______ the direction of the magnetic field.
Reversing the direction in which the current flows through the wire will reverse the direction of the magnetic field.
What two factors does the strength of the magnetic field around a wire depend on?
The size of the current and the distance from the conductor.
True or False?
Field lines around a current-carrying wire get closer together as the current increases.
True.
A larger current produces a stronger magnetic field, shown by field lines becoming more closely spaced.
Define solenoid.
A wire looped into a coil, which increases the strength of the magnetic field compared to a single wire.
What is the magnetic field like inside a solenoid?
Strong and uniform, running along the centre of the solenoid.
Why is the field inside a solenoid strong while the field outside it is weak?
Inside, the fields from individual coils add together; outside, they cancel.
Viewed from the end of a solenoid, current travelling clockwise indicates which pole?
The south pole.
The strength of the magnetic field around a solenoid can be increased by increasing the current, increasing the ______ in the coil, or adding an ______.
The strength of the magnetic field around a solenoid can be increased by increasing the current, increasing the number of turns in the coil, or adding an iron core.
Why does adding an iron core through a solenoid increase its overall magnetic strength?
The iron core becomes an induced magnet when current flows, and its field combines with the solenoid's field to create a much stronger magnet.
True or False?
The individual loops of a coil should be called "more coils" rather than "turns".
False.
The coil describes the overall object; the individual loops should be called turns, so the correct phrase is "add more turns to the coil".
Define the motor effect.
When a wire with current flowing through it is placed in a magnetic field and experiences a force.
What causes the force on a current-carrying wire in the motor effect?
The interaction of two magnetic fields: the field around the wire due to its current, and the external field it is placed in.
Name two ways to increase the force on a current-carrying wire in a magnetic field.
Increase the current, use a stronger magnet, or place the wire at 90° to the field.
At what angle to the magnetic field should a current-carrying wire be placed to produce the maximum force?
90° to the magnetic field lines.
If the two magnetic fields are ______, there will be no interaction between them and therefore ______.
If the two magnetic fields are parallel, there will be no interaction between them and therefore no force produced.
True or False?
Using a weaker magnet increases the force on a current-carrying wire.
False.
Stronger magnetic fields produce stronger forces, so a weaker magnet would decrease the force.
What three quantities does Fleming's left-hand rule relate?
The directions of the force (thrust), the magnetic field, and the current.
How are the force, field and current directions arranged relative to each other in Fleming's left-hand rule?
They are all perpendicular to each other.
Define what each finger and thumb represent in Fleming's left-hand rule.
First finger = Field, seCond finger = Current, THumb = THrust (force).
The magnetic field is always in the direction from ______ to ______, and current is always in the direction of a positive terminal to a negative terminal.
The magnetic field is always in the direction from North to South, and current is always in the direction of a positive terminal to a negative terminal.
True or False?
The force on a current-carrying wire in a magnetic field can only ever act left or right in the plane of the page.
False.
Because the force, field and current are all perpendicular to each other, the force can act into or out of the page as well.
Define magnetic flux density, B.
The strength of a magnetic field, measured in tesla (T).
State the equation for the force on a current-carrying conductor in a magnetic field.
$F = B I L$
In the equation F = BIL, what do I and L represent?
I is the current through the conductor (A); L is the length of conductor in the magnetic field (m).
In F = BIL, F is measured in ______, B in ______, and L in metres.
In F = BIL, F is measured in newtons, B in tesla, and L in metres.
True or False?
You may be asked to calculate the force on a wire at any angle to the magnetic field.
False.
You will only be expected to calculate the force when the wire is perpendicular (90°) to the field.
A wire perpendicular to a magnetic field carries a current of 1.5 A and experiences a force of 0.06 N over a length of 0.05 m. Calculate the magnetic flux density.
$B = \frac{F}{I L} = \frac{0.06}{1.5 \times 0.05} = 0.8 T$
What are the two key components that connect the rotating coil of a d.c. motor to the circuit?
A split ring and carbon brushes.
Why do the two sides of a current-carrying coil in a d.c. motor experience forces in opposite directions?
Current flows in opposite directions along each side of the coil, so Fleming's left-hand rule gives forces in opposite directions, causing rotation.
Why does the coil in a d.c. motor keep rotating when it passes through the vertical position, even though no force acts on it there?
The momentum of the coil carries it past the vertical position until the split ring reconnects with the brushes.
Define split-ring commutator.
A circular tube of metal split in two, connected to the coil, which reverses the connection to the circuit every half rotation so the coil keeps turning in the same direction.
The direction of rotation of the coil in a d.c. motor can be changed by reversing the direction of the current supply, or by reversing the ______ of the magnet.
The direction of rotation of the coil in a d.c. motor can be changed by reversing the direction of the current supply, or by reversing the poles of the magnet.
Name three ways to increase the force supplied by a d.c. motor.
Increase the current in the coil, increase the strength of the magnetic field, or add more turns to the coil.
True or False?
When the coil of a d.c. motor is vertical, current still flows through it and a force still acts on it.
False.
When vertical, the split ring is not in contact with the brushes, so no current flows and no force acts.

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