Define magnetic flux .

Magnetic flux is the product of the magnetic flux density and the cross-sectional area perpendicular to the direction of the magnetic flux density.

Magnetic flux is a maximum when the magnetic field lines are .......... to the plane of the area.

Magnetic flux is a maximum when the magnetic field lines are perpendicular to the plane of the area.

True or False? Magnetic flux is zero when the magnetic field lines are perpendicular to the plane of the area.

False. Magnetic flux is maximum when the field lines are perpendicular to the plane of the area, and zero when they are parallel to it.

Under what condition is magnetic flux at its minimum?

When the magnetic field lines are parallel to the plane of the area.

Define magnetic flux linkage .

Magnetic flux linkage is the product of the magnetic flux and the number of turns of the coil.

Magnetic flux linkage has units of .......... .

Magnetic flux linkage has units of Weber turns (Wb turns).

State three things that can cause an e.m.f. to be induced due to changing flux linkage.

A changing magnetic flux density, B A changing cross-sectional area, A A changing angle, θ

True or False? Magnetic flux linkage is at its maximum when θ = 90°.

False. Flux linkage is maximum (= BAN ) when θ = 0°, since cos(0°) = 1. At θ = 90°, cos( θ ) = 0, so the flux linkage is zero .

Define electromagnetic induction .

Electromagnetic induction is the process by which an e.m.f. is induced in a circuit due to changes in magnetic flux.

Name two applications that use electromagnetic induction.

Generators , which convert mechanical energy to electrical energy Transformers , which are used in electrical power transmission

Under what two general conditions does electromagnetic induction occur?

A conductor cuts through a magnetic field The direction of a magnetic field through a coil changes

When a bar magnet is held .......... inside a coil, the voltmeter reads zero because the flux is not changing.

When a bar magnet is held stationary inside a coil, the voltmeter reads zero because the flux is not changing.

List three factors that increase the magnitude of the e.m.f. induced when a magnet is moved through a coil.

Moving the magnet faster through the coil Adding more turns to the coil Increasing the strength of the bar magnet

True or False? A current must already be flowing through a wire before it is moved between two magnets for an e.m.f. to be induced.

False. No current needs to be flowing beforehand; the motion of the wire through the magnetic field is what induces the e.m.f.

How does the direction of the induced e.m.f. change as a bar magnet is withdrawn from a coil, compared to when it was inserted?

The induced e.m.f. reverses direction (the voltmeter reading has the opposite sign).

Define Faraday's law .

The magnitude of the induced e.m.f. is directly proportional to the rate of change of magnetic flux linkage.

The induced e.m.f. acts in such a direction as to produce effects that oppose the change causing it.

To verify Lenz's law, a bar magnet, a coil of wire and a sensitive .......... are needed.

To verify Lenz's law, a bar magnet, a coil of wire and a sensitive ammeter are needed.

True or False? A cell is required to verify Lenz's law using a bar magnet and a coil.

False. No cell is needed; moving the magnet through the coil induces the current, which is measured on the ammeter.

Under what condition is the e.m.f. induced in a moving conductor at its maximum?

When the conductor moves perpendicular to the magnetic field lines.

The e.m.f. induced in a rotating coil is a maximum when the plane of the coil is .......... to the magnetic field lines.

The e.m.f. induced in a rotating coil is a maximum when the plane of the coil is parallel to the magnetic field lines.

True or False? The e.m.f. induced in a rotating coil is in phase with the magnetic flux linkage.

False. The e.m.f. and flux linkage are 90° out of phase ; the e.m.f. is maximum when the flux linkage is zero, and vice versa.

Name three factors that increase the e.m.f. induced in a conductor moving through a magnetic field.

A longer conductor in the field A stronger magnetic field The conductor cutting through the field lines faster

At what angle θ is the e.m.f. induced in a rotating coil equal to zero?

θ = 0°, when the field lines are perpendicular to the plane of the coil (flux linkage is maximum).

What is the independent variable in the search coil flux linkage experiment?

The angle , θ , between the normal to the search coil and the magnetic field lines.

List the four control variables in the search coil flux linkage experiment.

Area of the search coil, A Number of loops on both coils, N Magnetic field strength, B Frequency of the power supply, f

A graph of peak e.m.f. ε 0 against .......... produces a straight line.

A graph of peak e.m.f. ε 0 against cos(θ) produces a straight line.

How is the peak e.m.f., ε 0 , obtained from the CRO trace?

Read the peak-to-peak voltage ( V pp ) from the CRO and halve it .

True or False? A systematic error in this experiment can arise because the magnetic field lines are perfectly parallel and perpendicular to the search coil at all times.

False. The field lines are unlikely to be perfectly parallel and perpendicular to the coil, which causes the graph to have a y-intercept at cos( θ ) = 0.

Suggest one way to improve the reliability of the search coil flux linkage experiment.

Repeat the experiment for a full turn ( θ = 360°), or use a calibrated motor to rotate the coil by fixed increments.

State one safety consideration for the search coil flux linkage experiment.

Keep water or fluids away from the electrical equipment, and do not exceed the specified current rating for the coil to avoid overheating.

A LevelPhysicsAQAFlashcardsFields & Their ConsequencesElectromagnetic Induction

Electromagnetic Induction (AQA A Level Physics): Flashcards

Exam code: 7408

1/43

0Still learning

Know0

FrontMagnetic Flux
Define magnetic flux.

Was this flashcard helpful?

Cards in this collection (43)

Define magnetic flux.
Magnetic flux is the product of the magnetic flux density and the cross-sectional area perpendicular to the direction of the magnetic flux density.
What is the equation for magnetic flux, Φ?
$Φ = B A$
Where B is the magnetic flux density and A is the cross-sectional area.
Magnetic flux is a maximum when the magnetic field lines are .......... to the plane of the area.
Magnetic flux is a maximum when the magnetic field lines are perpendicular to the plane of the area.
What is the unit of magnetic flux?
The Weber (Wb).
True or False?
Magnetic flux is zero when the magnetic field lines are perpendicular to the plane of the area.
False.
Magnetic flux is maximum when the field lines are perpendicular to the plane of the area, and zero when they are parallel to it.
Under what condition is magnetic flux at its minimum?
When the magnetic field lines are parallel to the plane of the area.
What is the symbol used for magnetic flux?
$Φ$ (the Greek letter phi).
Define magnetic flux linkage.
Magnetic flux linkage is the product of the magnetic flux and the number of turns of the coil.
What is the equation for magnetic flux linkage when the field is perpendicular to the coil?
$N Φ = B A N$
What is the equation for magnetic flux linkage when the field lines make an angle θ with the normal to the coil?
$N Φ = B A N \cos (θ)$
Magnetic flux linkage has units of ...........
Magnetic flux linkage has units of Weber turns (Wb turns).
State three things that can cause an e.m.f. to be induced due to changing flux linkage.
- A changing magnetic flux density, B
- A changing cross-sectional area, A
- A changing angle, θ
True or False?
Magnetic flux linkage is at its maximum when θ = 90°.
False.
Flux linkage is maximum (= BAN) when θ = 0°, since cos(0°) = 1. At θ = 90°, cos(θ) = 0, so the flux linkage is zero.
What effect does increasing the number of turns on a coil have on the induced e.m.f.?
It induces a larger e.m.f.
Define electromagnetic induction.
Electromagnetic induction is the process by which an e.m.f. is induced in a circuit due to changes in magnetic flux.
Name two applications that use electromagnetic induction.
- Generators, which convert mechanical energy to electrical energy
- Transformers, which are used in electrical power transmission
Under what two general conditions does electromagnetic induction occur?
- A conductor cuts through a magnetic field
- The direction of a magnetic field through a coil changes
When a bar magnet is held .......... inside a coil, the voltmeter reads zero because the flux is not changing.
When a bar magnet is held stationary inside a coil, the voltmeter reads zero because the flux is not changing.
List three factors that increase the magnitude of the e.m.f. induced when a magnet is moved through a coil.
- Moving the magnet faster through the coil
- Adding more turns to the coil
- Increasing the strength of the bar magnet
True or False?
A current must already be flowing through a wire before it is moved between two magnets for an e.m.f. to be induced.
False.
No current needs to be flowing beforehand; the motion of the wire through the magnetic field is what induces the e.m.f.
How does the direction of the induced e.m.f. change as a bar magnet is withdrawn from a coil, compared to when it was inserted?
The induced e.m.f. reverses direction (the voltmeter reading has the opposite sign).
Define Faraday's law.
The magnitude of the induced e.m.f. is directly proportional to the rate of change of magnetic flux linkage.
Define Lenz's law.
The induced e.m.f. acts in such a direction as to produce effects that oppose the change causing it.
Write the equation combining Faraday's and Lenz's laws.
$ϵ = - N \frac{Δ Φ}{Δ t}$
What does the gradient of a graph of flux linkage against time represent?
The induced e.m.f.
To verify Lenz's law, a bar magnet, a coil of wire and a sensitive .......... are needed.
To verify Lenz's law, a bar magnet, a coil of wire and a sensitive ammeter are needed.
True or False?
A cell is required to verify Lenz's law using a bar magnet and a coil.
False.
No cell is needed; moving the magnet through the coil induces the current, which is measured on the ammeter.
What does the minus sign in $ϵ = - N \frac{Δ Φ}{Δ t}$ represent?
The coil's induced magnetic field acts in the opposite direction to the change producing it (Lenz's law).
What is the equation for the e.m.f. induced in a straight conductor of length L moving with velocity v perpendicular to a magnetic field of flux density B?
$ϵ = B L v$
Under what condition is the e.m.f. induced in a moving conductor at its maximum?
When the conductor moves perpendicular to the magnetic field lines.
The e.m.f. induced in a rotating coil is a maximum when the plane of the coil is .......... to the magnetic field lines.
The e.m.f. induced in a rotating coil is a maximum when the plane of the coil is parallel to the magnetic field lines.
Write the equation for the e.m.f. induced in a coil of N turns and area A rotating with angular speed ω in a magnetic field of flux density B.
$ϵ = B A N ω \sin (ω t)$
True or False?
The e.m.f. induced in a rotating coil is in phase with the magnetic flux linkage.
False.
The e.m.f. and flux linkage are 90° out of phase; the e.m.f. is maximum when the flux linkage is zero, and vice versa.
Name three factors that increase the e.m.f. induced in a conductor moving through a magnetic field.
- A longer conductor in the field
- A stronger magnetic field
- The conductor cutting through the field lines faster
At what angle θ is the e.m.f. induced in a rotating coil equal to zero?
θ = 0°, when the field lines are perpendicular to the plane of the coil (flux linkage is maximum).
What is the independent variable in the search coil flux linkage experiment?
The angle, θ, between the normal to the search coil and the magnetic field lines.
What is the dependent variable in the search coil flux linkage experiment?
The induced e.m.f., ε.
List the four control variables in the search coil flux linkage experiment.
- Area of the search coil, A
- Number of loops on both coils, N
- Magnetic field strength, B
- Frequency of the power supply, f
A graph of peak e.m.f. ε₀ against .......... produces a straight line.
A graph of peak e.m.f. ε₀ against cos(θ) produces a straight line.
How is the peak e.m.f., ε₀, obtained from the CRO trace?
Read the peak-to-peak voltage (V_pp) from the CRO and halve it.
True or False?
A systematic error in this experiment can arise because the magnetic field lines are perfectly parallel and perpendicular to the search coil at all times.
False.
The field lines are unlikely to be perfectly parallel and perpendicular to the coil, which causes the graph to have a y-intercept at cos(θ) = 0.
Suggest one way to improve the reliability of the search coil flux linkage experiment.
Repeat the experiment for a full turn (θ = 360°), or use a calibrated motor to rotate the coil by fixed increments.
State one safety consideration for the search coil flux linkage experiment.
Keep water or fluids away from the electrical equipment, and do not exceed the specified current rating for the coil to avoid overheating.

Sign up to unlock flashcards

By signing up you agree to our Terms and Privacy Policy

Previous:Magnetic FieldsNext:Alternating Currents & Transformers