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 ways to increase the magnitude of the e.m.f induced when a magnet is moved through a coil.

Move the magnet faster through the coil Add more turns to the coil Use a stronger magnet

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

False. An e.m.f is only induced when the magnetic flux is changing . A stationary magnet gives a zero rate of change of flux , so no e.m.f is induced.

What type of voltage is induced when a coil rotates in a uniform magnetic field?

An alternating voltage , because the flux linkage through the coil continually varies as it rotates, inducing a varying e.m.f.

During the rotation of a coil in a uniform field, at what position is the induced e.m.f a maximum ?

When the coil cuts through the most field lines (at θ = 90°), where the rate of change of flux linkage is greatest — not where the flux linkage itself is greatest.

During electromagnetic induction, mechanical work from moving the conductor in the field is transformed into .......... .

During electromagnetic induction, mechanical work from moving the conductor in the field is transformed into electrical energy .

A transformer is a device that works by electromagnetic induction , changing a high alternating voltage at low current to a low alternating voltage at high current , and vice versa.

Name the three main components of a transformer .

A primary coil A secondary coil A soft iron core

Why is soft iron used for the core of a transformer?

Because it is easily magnetised and demagnetised , and it creates flux linkage between the primary and secondary coils.

How does the frequency of the secondary (output) voltage compare with the primary (input) voltage?

It is the same frequency as the input voltage.

An alternating current in the primary coil creates a changing magnetic flux linkage in the secondary coil, which induces an .......... by Faraday's Law.

An alternating current in the primary coil creates a changing magnetic flux linkage in the secondary coil, which induces an e.m.f by Faraday's Law.

A transformer can operate on a steady direct current . True or False?

False. A transformer needs a changing (alternating) current . A steady d.c. gives a constant magnetic flux, so there is no change in flux linkage and no continuously induced e.m.f — an e.m.f appears only momentarily as the d.c. is switched on or off.

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

What apparatus is needed to verify Lenz's Law ?

A bar magnet A coil of wire A sensitive ammeter

When a north pole is pushed into a coil, which pole is induced at the coil face, and why?

A north pole is induced, so that it repels the incoming magnet and opposes the change causing the e.m.f.

Lenz's Law is a direct consequence of the principle of conservation of .......... .

Lenz's Law is a direct consequence of the principle of conservation of energy .

A cell is required to verify Lenz's Law. True or False?

False. No cell is needed. The moving magnet itself induces the e.m.f that drives the current through the sensitive ammeter.

State Faraday's Law .

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

On a graph of magnetic flux linkage against time , what does the gradient represent?

The magnitude of the induced e.m.f .

The induced e.m.f depends on the amount of flux linkage, not on its rate of change. True or False?

False. Faraday's Law states the e.m.f depends on the rate of change of flux linkage, not the amount of flux linkage. The e.m.f can be zero even when the flux linkage is at a maximum.

Define alternating current (a.c.) .

An alternating current is a current which periodically varies between a positive and negative value ; its direction switches every half cycle .

Define peak current (or peak voltage).

The maximum value of the alternating current (or voltage).

The peak-to-peak voltage is the distance between a positive peak and a consecutive .......... peak.

The peak-to-peak voltage is the distance between a positive peak and a consecutive negative peak.

What do rms values of current and voltage allow you to do?

They allow an a.c. value to be compared to its equivalent d.c. — the direct value that produces the same heating effect (power dissipation) .

In an a.c. circuit, the electrons drift steadily in one direction . True or False?

False. In a.c. the electrons move back and forth with simple harmonic motion , because the current periodically reverses direction.

The rms current is equal to 0.707 × I 0 , which is about 70% of the .......... current.

The rms current is equal to 0.707 × I 0 , which is about 70% of the peak current.

How is the peak-to-peak voltage related to the peak voltage?

Peak-to-peak voltage = peak voltage ( V 0 ) × 2 .

The peak value of an a.c. current gives the equivalent d.c. that produces the same heating effect. True or False?

False. It is the rms value (not the peak value) that is equivalent to the direct current producing the same power / heating effect .

An oven is connected to a 230 V rms mains supply. Calculate the peak-to-peak voltage .

Peak-to-peak = (√2 × V rms ) × 2 = (√2 × 230) × 2 = 651 V (3 s.f.).

A LevelPhysicsEdexcelFlashcards7. Electric & Magnetic FieldsElectromagnetic Induction & Alternating Currents

Electromagnetic Induction & Alternating Currents (Edexcel A Level Physics): Flashcards

Exam code: 9PH0

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FrontInduced E.M.F in a Moving Coil
Define electromagnetic induction.
FrontInduced E.M.F in a Moving Coil
State three ways to increase the magnitude of the e.m.f induced when a magnet is moved through a coil.
BackInduced E.M.F in a Moving Coil
Move the magnet faster through the coil
Add more turns to the coil
Use a stronger magnet

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Cards in this collection (37)

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 ways to increase the magnitude of the e.m.f induced when a magnet is moved through a coil.
- Move the magnet faster through the coil
- Add more turns to the coil
- Use a stronger magnet
A magnet held stationary inside a coil induces an e.m.f.
True or False?
False.
An e.m.f is only induced when the magnetic flux is changing. A stationary magnet gives a zero rate of change of flux, so no e.m.f is induced.
What type of voltage is induced when a coil rotates in a uniform magnetic field?
An alternating voltage, because the flux linkage through the coil continually varies as it rotates, inducing a varying e.m.f.
During the rotation of a coil in a uniform field, at what position is the induced e.m.f a maximum?
When the coil cuts through the most field lines (at θ = 90°), where the rate of change of flux linkage is greatest — not where the flux linkage itself is greatest.
During electromagnetic induction, mechanical work from moving the conductor in the field is transformed into ...........
During electromagnetic induction, mechanical work from moving the conductor in the field is transformed into electrical energy.
Define transformer.
A transformer is a device that works by electromagnetic induction, changing a high alternating voltage at low current to a low alternating voltage at high current, and vice versa.
Name the three main components of a transformer.
- A primary coil
- A secondary coil
- A soft iron core
Why is soft iron used for the core of a transformer?
Because it is easily magnetised and demagnetised, and it creates flux linkage between the primary and secondary coils.
How does the frequency of the secondary (output) voltage compare with the primary (input) voltage?
It is the same frequency as the input voltage.
An alternating current in the primary coil creates a changing magnetic flux linkage in the secondary coil, which induces an .......... by Faraday's Law.
An alternating current in the primary coil creates a changing magnetic flux linkage in the secondary coil, which induces an e.m.f by Faraday's Law.
A transformer can operate on a steady direct current.
True or False?
False.
A transformer needs a changing (alternating) current. A steady d.c. gives a constant magnetic flux, so there is no change in flux linkage and no continuously induced e.m.f — an e.m.f appears only momentarily as the d.c. is switched on or off.
State Lenz's Law.
The induced e.m.f is set up in a direction to produce effects that oppose the change causing it.
What apparatus is needed to verify Lenz's Law?
- A bar magnet
- A coil of wire
- A sensitive ammeter
When a north pole is pushed into a coil, which pole is induced at the coil face, and why?
A north pole is induced, so that it repels the incoming magnet and opposes the change causing the e.m.f.
Lenz's Law is a direct consequence of the principle of conservation of ...........
Lenz's Law is a direct consequence of the principle of conservation of energy.
In the equation $ϵ = - \frac{d (N Φ)}{d t}$ , what does the negative sign represent?
Lenz's Law — the induced e.m.f is set up to oppose the change in flux linkage that causes it.
A cell is required to verify Lenz's Law.
True or False?
False.
No cell is needed. The moving magnet itself induces the e.m.f that drives the current through the sensitive ammeter.
State Faraday's Law.
The magnitude of the induced e.m.f is directly proportional to the rate of change of magnetic flux linkage.
Write the equation for Faraday's Law and define each term.
$ϵ = \frac{Δ (N Φ)}{Δ t}$
- ε = induced e.m.f (V)
- Δ(NΦ) = change in flux linkage (Wb turns)
- Δt = time interval (s)
What are the units of magnetic flux linkage?
Weber turns (Wb turns).
On a graph of magnetic flux linkage against time, what does the gradient represent?
The magnitude of the induced e.m.f.
In the equation $ϵ = - \frac{d (N Φ)}{d t}$ , the negative sign represents ...........
In the equation $ϵ = - \frac{d (N Φ)}{d t}$ , the negative sign represents Lenz's Law.
The induced e.m.f depends on the amount of flux linkage, not on its rate of change.
True or False?
False.
Faraday's Law states the e.m.f depends on the rate of change of flux linkage, not the amount of flux linkage. The e.m.f can be zero even when the flux linkage is at a maximum.
Define alternating current (a.c.).
An alternating current is a current which periodically varies between a positive and negative value; its direction switches every half cycle.
What shape is the current–time graph of an a.c. supply?
Sinusoidal (a sine curve).
State the relationship between time period *T and frequency f*.
$T = \frac{1}{f}$
where T = time period (s) and f = frequency (Hz).
Define peak current (or peak voltage).
The maximum value of the alternating current (or voltage).
The peak-to-peak voltage is the distance between a positive peak and a consecutive .......... peak.
The peak-to-peak voltage is the distance between a positive peak and a consecutive negative peak.
What do rms values of current and voltage allow you to do?
They allow an a.c. value to be compared to its equivalent d.c. — the direct value that produces the same heating effect (power dissipation).
In an a.c. circuit, the electrons drift steadily in one direction.
True or False?
False.
In a.c. the electrons move back and forth with simple harmonic motion, because the current periodically reverses direction.
Write the equations relating rms current and rms voltage to their peak values.
$I_{r m s} = \frac{I_{0}}{\sqrt{2}}$
$V_{r m s} = \frac{V_{0}}{\sqrt{2}}$
where I₀ = peak current and V₀ = peak voltage.
The rms current is equal to 0.707 × I₀, which is about 70% of the .......... current.
The rms current is equal to 0.707 × I₀, which is about 70% of the peak current.
How do you calculate the peak voltage from the rms voltage?
$V_{0} = \sqrt{2} \times V_{r m s}$
How is the peak-to-peak voltage related to the peak voltage?
Peak-to-peak voltage = peak voltage (V₀) × 2.
The peak value of an a.c. current gives the equivalent d.c. that produces the same heating effect.
True or False?
False.
It is the rms value (not the peak value) that is equivalent to the direct current producing the same power / heating effect.
An oven is connected to a 230 V rms mains supply. Calculate the peak-to-peak voltage.
Peak-to-peak = (√2 × V_rms) × 2 = (√2 × 230) × 2 = 651 V (3 s.f.).

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