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

Magnetic flux is at a minimum when the magnetic field lines are parallel to the plane of the area.

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

False. Magnetic flux is maximum when the field lines are perpendicular to the plane of the area (θ = 0° to the normal); it is zero when the field lines are parallel to the plane.

Define Fleming's Left Hand Rule for a charged particle.

Fleming's Left Hand Rule : First finger = direction of the magnetic field Second finger = direction of conventional current (velocity of a moving positive charge) Thumb = direction of the magnetic force

Why does the magnetic force on a charged particle act as a centripetal force?

Because the force is always perpendicular to the particle's velocity, which causes it to move in a circular path.

What do a dot and a cross represent when showing a magnetic field in a 2D diagram?

A dot represents the field directed out of the page A cross represents the field directed into the page

For a negatively charged particle, such as an electron, the second finger in Fleming's Left Hand Rule points in the .......... direction to the particle's motion.

For a negatively charged particle, such as an electron, the second finger in Fleming's Left Hand Rule points in the opposite direction to the particle's motion.

True or False? A charged particle moving parallel to a magnetic field experiences the maximum possible magnetic force.

False. A charged particle moving parallel to a magnetic field experiences zero force; the maximum force occurs when the particle's velocity is perpendicular to the field.

Define Fleming's Left Hand Rule for a current-carrying conductor.

Fleming's Left Hand Rule : First finger = direction of the magnetic field Second finger = direction of conventional current Thumb = direction of the magnetic force

Which direction is used for 'current' when applying Fleming's Left Hand Rule?

The direction of conventional current — the flow of positive charge — which is opposite to the direction of electron flow.

A current-carrying conductor experiences .......... if the current flows parallel to the magnetic field lines.

A current-carrying conductor experiences no force if the current flows parallel to the magnetic field lines.

Define electromagnetic induction .

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

State three factors that increase the magnitude of an e.m.f. induced by moving a bar magnet through a coil.

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

What does a voltmeter read when a bar magnet is held stationary inside a coil?

Zero. There is no change in flux, so no e.m.f. is induced.

As a coil rotates in a uniform magnetic field, at what angular position is the induced e.m.f. a maximum, and why?

At θ = 90° to the field. Although the flux linkage is minimum here, the rate of change of flux linkage is at its maximum, so the induced e.m.f. is greatest.

Increasing a coil's frequency of rotation increases both the frequency and the .......... of the alternating voltage.

Increasing a coil's frequency of rotation increases both the frequency and the amplitude of the alternating voltage.

True or False? A bar magnet held stationary inside a coil induces a constant e.m.f.

False. A stationary magnet produces no change in flux, so no e.m.f. is induced at all.

Define a transformer .

A transformer is a device that uses electromagnetic induction to change high alternating voltage at low current into low alternating voltage at high current, and vice versa.

Why is a soft iron core used in a transformer?

It creates flux linkage between the primary and secondary coils, and can be easily magnetised and demagnetised .

What happens in the secondary coil while a steady direct current flows in the primary coil?

There is no change in magnetic flux linkage, so the induced e.m.f. (and current) falls to zero .

When a direct current in the primary coil is switched off, an e.m.f. is induced in the secondary coil in the .......... direction compared with when it was switched on.

When a direct current in the primary coil is switched off, an e.m.f. is induced in the secondary coil in the opposite direction compared with when it was switched on.

True or False? A steady direct current in the primary coil continuously induces an e.m.f. in the secondary coil.

False. Only a changing current (and therefore changing flux) induces an e.m.f.; once the direct current is steady, the induced e.m.f. falls to zero.

The induced e.m.f. is set up in a direction to produce effects that oppose the change causing it.

What does the gradient of a graph of magnetic flux linkage against time represent?

The magnitude of the induced e.m.f.

According to Lenz's Law, a north pole approaching a coil induces a .......... pole at the near face of the coil, since like poles repel.

According to Lenz's Law, a north pole approaching a coil induces a north pole at the near face of the coil, since like poles repel.

True or False? The minus sign in Faraday's Law must always be included when calculating the magnitude of an induced e.m.f.

False. The magnitude of the e.m.f. is just its size, so the minus sign is not needed for magnitude calculations — it is only required to indicate direction, as an expression of Lenz's Law .

International A Level (IAL)PhysicsEdexcelFlashcards4. Further Mechanics, Fields & ParticlesMagnetic Fields

Magnetic Fields (Edexcel International A Level (IAL) Physics): Flashcards

Exam code: YPH11

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FrontMagnetic Flux Density, Flux & Flux Linkage
Define magnetic flux density.

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Cards in this collection (38)

Define magnetic flux density.
Magnetic flux density (B) is defined by rearranging the equation for the magnetic force on a current-carrying conductor:
$B = \frac{F}{I L}$
It is measured in tesla (T).
Define magnetic flux.
Magnetic flux (Φ) is the product of the magnetic flux density and the cross-sectional area perpendicular to the field:
$Φ = B A$
It is measured in webers (Wb).
Define magnetic flux linkage.
Magnetic flux linkage is the product of the magnetic flux and the number of turns N of a coil:
$N Φ = B A N$
It is measured in weber turns (Wb turns).
What equation gives the magnetic flux through a coil when the field lines make an angle θ with the normal to the plane of the coil?
$Φ = B A \cos θ$
At what angle θ between the field lines and the normal is magnetic flux at a maximum, and why?
Magnetic flux is maximum when θ = 0°, because $\cos θ = 1$ when the field lines are perpendicular to the plane of the area (parallel to the normal).
Magnetic flux is at a .......... when the magnetic field lines are parallel to the plane of the area.
Magnetic flux is at a minimum when the magnetic field lines are parallel to the plane of the area.
True or False?
Magnetic flux is maximum when the magnetic field lines are parallel to the plane of the area.
False.
Magnetic flux is maximum when the field lines are perpendicular to the plane of the area (θ = 0° to the normal); it is zero when the field lines are parallel to the plane.
What is the equation for the maximum magnetic force on an isolated moving charged particle?
$F = B Q v$
This is the maximum force, occurring when F, B and v are mutually perpendicular.
What is the general equation for the magnetic force on a charged particle moving at angle θ to a magnetic field?
$F = B Q v \sin θ$
Define Fleming's Left Hand Rule for a charged particle.
Fleming's Left Hand Rule:
- First finger = direction of the magnetic field
- Second finger = direction of conventional current (velocity of a moving positive charge)
- Thumb = direction of the magnetic force
Why does the magnetic force on a charged particle act as a centripetal force?
Because the force is always perpendicular to the particle's velocity, which causes it to move in a circular path.
What do a dot and a cross represent when showing a magnetic field in a 2D diagram?
- A dot represents the field directed out of the page
- A cross represents the field directed into the page
For a negatively charged particle, such as an electron, the second finger in Fleming's Left Hand Rule points in the .......... direction to the particle's motion.
For a negatively charged particle, such as an electron, the second finger in Fleming's Left Hand Rule points in the opposite direction to the particle's motion.
True or False?
A charged particle moving parallel to a magnetic field experiences the maximum possible magnetic force.
False.
A charged particle moving parallel to a magnetic field experiences zero force; the maximum force occurs when the particle's velocity is perpendicular to the field.
What is the equation for the magnetic force on a current-carrying conductor at angle θ to a magnetic field?
$F = B I L \sin θ$
Under what condition is the force on a current-carrying conductor at a maximum, and what does the equation simplify to?
The force is maximum when the conductor is perpendicular to the field (θ = 90°, sin θ = 1):
$F = B I L$
Define Fleming's Left Hand Rule for a current-carrying conductor.
Fleming's Left Hand Rule:
- First finger = direction of the magnetic field
- Second finger = direction of conventional current
- Thumb = direction of the magnetic force
Which direction is used for 'current' when applying Fleming's Left Hand Rule?
The direction of conventional current — the flow of positive charge — which is opposite to the direction of electron flow.
A current-carrying conductor experiences .......... if the current flows parallel to the magnetic field lines.
A current-carrying conductor experiences no force if the current flows parallel to the magnetic field lines.
True or False?
The magnetic force on a current-carrying conductor depends on the conductor's resistance.
False.
The force depends on the magnetic flux density B, current I, length L and $\sin θ$ — not on the conductor's resistance.
Define electromagnetic induction.
Electromagnetic induction is the process in which an e.m.f. is induced in a closed circuit due to changes in magnetic flux (linkage).
State three factors that increase the magnitude of an e.m.f. induced by moving a bar magnet through a coil.
- Moving the magnet faster through the coil
- Adding more turns to the coil
- Increasing the strength of the magnet
What does a voltmeter read when a bar magnet is held stationary inside a coil?
Zero. There is no change in flux, so no e.m.f. is induced.
As a coil rotates in a uniform magnetic field, at what angular position is the induced e.m.f. a maximum, and why?
At θ = 90° to the field. Although the flux linkage is minimum here, the rate of change of flux linkage is at its maximum, so the induced e.m.f. is greatest.
Increasing a coil's frequency of rotation increases both the frequency and the .......... of the alternating voltage.
Increasing a coil's frequency of rotation increases both the frequency and the amplitude of the alternating voltage.
True or False?
A bar magnet held stationary inside a coil induces a constant e.m.f.
False.
A stationary magnet produces no change in flux, so no e.m.f. is induced at all.
Define a transformer.
A transformer is a device that uses electromagnetic induction to change high alternating voltage at low current into low alternating voltage at high current, and vice versa.
Why is a soft iron core used in a transformer?
It creates flux linkage between the primary and secondary coils, and can be easily magnetised and demagnetised.
What happens in the secondary coil while a steady direct current flows in the primary coil?
There is no change in magnetic flux linkage, so the induced e.m.f. (and current) falls to zero.
How does the frequency of the output voltage in the secondary coil compare with the input frequency in the primary coil?
They are the same frequency.
When a direct current in the primary coil is switched off, an e.m.f. is induced in the secondary coil in the .......... direction compared with when it was switched on.
When a direct current in the primary coil is switched off, an e.m.f. is induced in the secondary coil in the opposite direction compared with when it was switched on.
True or False?
A steady direct current in the primary coil continuously induces an e.m.f. in the secondary coil.
False.
Only a changing current (and therefore changing flux) induces an e.m.f.; once the direct current is steady, the induced e.m.f. falls to zero.
Define Faraday's Law.
The magnitude of the induced e.m.f. is directly proportional to the rate of change of magnetic flux linkage:
$ε = \frac{Δ (N Φ)}{Δ t}$
Define Lenz's Law.
The induced e.m.f. is set up in a direction to produce effects that oppose the change causing it.
What does the negative sign represent in the equation $ε = - \frac{d (N Φ)}{d t}$ ?
Lenz's Law — the induced e.m.f. is set up in the opposite direction to oppose the changing flux linkage.
What does the gradient of a graph of magnetic flux linkage against time represent?
The magnitude of the induced e.m.f.
According to Lenz's Law, a north pole approaching a coil induces a .......... pole at the near face of the coil, since like poles repel.
According to Lenz's Law, a north pole approaching a coil induces a north pole at the near face of the coil, since like poles repel.
True or False?
The minus sign in Faraday's Law must always be included when calculating the magnitude of an induced e.m.f.
False.
The magnitude of the e.m.f. is just its size, so the minus sign is not needed for magnitude calculations — it is only required to indicate direction, as an expression of Lenz's Law.

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