Define electromagnetic induction .

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

True or False? For electromagnetic induction to occur there must be relative motion between a conductor and a magnetic field.

True. For electromagnetic induction to occur there must be relative motion between a conductor and a magnetic field. This could be achieved by, for example, moving a conductor through a magnetic field, or moving a magnet through a coil.

Define induced e.m.f. in a conductor.

The induced e.m.f. in a conductor is the amount of work done per unit charge in separating the charges to the ends of the conductor.

How is an e.m.f. induced when a conductor cuts through magnetic field lines?

When a conductor cuts through magnetic field lines, an e.m.f. is induced as: free electrons (in the conductor) experience a magnetic force the magnetic force causes charges to separate the charge separation produces a potential difference (e.m.f.) across the ends of the conductor

True or False? An e.m.f. can be induced in a conductor without connecting it to a circuit.

True. An e.m.f. can be induced in a conductor without connecting it to a circuit. However, an induced current will only flow if the conductor is connected to a closed circuit.

How can the magnitude of an induced e.m.f. be increased?

The magnitude of an induced e.m.f. can be increased by increasing the length of the conductor in the field increasing the magnetic field strength increasing the velocity of the conductor increasing the number of turns of wire

Define magnetic flux .

Magnetic flux is the product of magnetic flux density and the area perpendicular to the field lines. It is a measure of the number of field lines in a given area.

One weber (Wb) is equal to 1 tesla multiplied by 1 metre squared (1 Wb = 1 T m 2 )

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

True. Magnetic flux is zero when the magnetic field lines are parallel to the area.

Define magnetic flux linkage .

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

True or False? Magnetic flux is sometimes measured in units of Wb-turns.

False. The unit of magnetic flux is the Weber (Wb). Magnetic flux linkage is sometimes described in units of Wb-turns.

State Faraday's law of induction .

Faraday's law of induction states the magnitude of an induced e.m.f is directly proportional to the rate of change of magnetic flux linkage .

When is a maximum e.m.f induced in a rectangular coil rotating in a magnetic field?

The induced e.m.f is at a maximum when the plane of the coil is parallel to the magnetic field lines. The sides of the coil cut the field lines at the fastest rate at this position.

True or False? No e.m.f is induced when a rotating rectangular coil is perpendicular to the magnetic field lines.

True. No e.m.f is induced when a rotating rectangular coil is perpendicular to the magnetic field lines.

True or False? Faraday's Law applies only to coils of wire.

False. Faraday's Law applies to any conductor experiencing a change in magnetic flux linkage.

How does increasing the number of turns on a coil affect the magnitude of an induced e.m.f?

Increasing the number of turns in a coil increases the induced e.m.f for a given rate of change of magnetic flux.

Lenz's law states the induced e.m.f in a coil or wire is such that it will oppose the change causing it.

True or False? Lenz's Law is a consequence of the principle of conservation of energy.

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

What happens to the direction of induced current when the direction of a magnet's motion is reversed?

When the direction of a magnet's motion is reversed, the direction of the induced current is also reversed.

What is self-induction ?

Self-induction is the effect in which a change in the current tends to produce an induced e.m.f. which opposes the change of current in the same circuit

What is mutual induction ?

Mutual induction is the effect in which a change in the current in one circuit tends to produce an induced e.m.f. which opposes the change of current in a neighbouring circuit

True or False? The back e.m.f. in self-induction is directly proportional to the rate of current change.

False. The back e.m.f. in self-induction is proportional to minus the rate of current change

What is a transformer ?

A transformer is a device that changes high alternating voltage at low current to low alternating voltage at high current, and vice versa.

What is the role of the soft iron core in a transformer?

The role of the soft iron core in a transformer is to significantly increase the strength of the magnetic field from the primary to the secondary coil.

True or False? In a step-up transformer, the primary coil has more turns than the secondary coil.

False. In a step-up transformer, the secondary coil has more turns than the primary coil

What is an A.C. generator ?

An A.C. generator is a device which converts energy from a mechanical store to an electrical store. The output of an A.C. generator is alternating current .

What components make up a simple A.C. generator?

A simple A.C. generator consists of the following components: a rectangular coil of wire rotating in a magnetic field slip rings and brushes

What is the purpose of slip rings in an A.C. generator?

The purpose of slip rings in an A.C. generator is to provide a continuous connection between the rotating coil and the external circuit.

How does the induced e.m.f. vary with time in an A.C. generator?

The induced e.m.f. varies sinusoidally with time in an A.C. generator and is 90° out of phase with the flux linkage The direction reverses every half rotation of the coil.

True or False? In an A.C. generator, the maximum e.m.f is induced when the magnetic flux linkage through the coil is at a maximum.

False. In an A.C. generator, when a maximum e.m.f is induced, the magnetic flux linkage is zero , but the change in flux linkage is at a maximum.

True or False? No e.m.f is induced when a rotating rectangular coil is perpendicular to magnetic field lines.

True. No e.m.f is induced when a rotating rectangular coil is perpendicular to magnetic field lines.

How can the size of the induced e.m.f. in a rotating coil be increased?

The size of the induced e.m.f in a rotating coil can be increased by increasing the frequency of rotation.

What is the effect of doubling the angular speed of a rotating coil on the induced e.m.f and frequency of rotation?

The effect of doubling the angular speed of a rotating coil is: the size of the induced e.m.f. doubles the frequency of the rotation doubles

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Define electromagnetic induction.
Electromagnetic induction is the process in which an e.m.f or current is induced in a closed circuit due to changes in magnetic flux.
True or False?
For electromagnetic induction to occur there must be relative motion between a conductor and a magnetic field.
True.
For electromagnetic induction to occur there must be relative motion between a conductor and a magnetic field.
This could be achieved by, for example, moving a conductor through a magnetic field, or moving a magnet through a coil.
Define induced e.m.f. in a conductor.
The induced e.m.f. in a conductor is the amount of work done per unit charge in separating the charges to the ends of the conductor.
How is an e.m.f. induced when a conductor cuts through magnetic field lines?
When a conductor cuts through magnetic field lines, an e.m.f. is induced as:
- free electrons (in the conductor) experience a magnetic force
- the magnetic force causes charges to separate
- the charge separation produces a potential difference (e.m.f.) across the ends of the conductor
True or False?
An e.m.f. can be induced in a conductor without connecting it to a circuit.
True.
An e.m.f. can be induced in a conductor without connecting it to a circuit.
However, an induced current will only flow if the conductor is connected to a closed circuit.
What is the induced e.m.f., $ε$ , in a straight conductor moving through a magnetic field?
The induced e.m.f. in a straight conductor is: $ε = B L v$
Where:
- $B$ = magnetic flux density (T)
- $L$ = length of the conductor in the field (m)
- $v$ = velocity of the conductor travelling through the field (m s^–1)
What is the induced e.m.f., $ε$ , in a coil with $N$ turns moving through a magnetic field?
The induced e.m.f. in a coil is: $ε = B L v N$
Where:
- $B$ = magnetic flux density (T)
- $L$ = length of the conductor in the field (m)
- $v$ = velocity of the conductor travelling through the field (m s^–1)
- $N$ = number of turns of wire in the coil
How can the magnitude of an induced e.m.f. be increased?
The magnitude of an induced e.m.f. can be increased by
- increasing the length of the conductor in the field
- increasing the magnetic field strength
- increasing the velocity of the conductor
- increasing the number of turns of wire
Define magnetic flux.
Magnetic flux is the product of magnetic flux density and the area perpendicular to the field lines.
It is a measure of the number of field lines in a given area.
Define 1 weber (Wb).
One weber (Wb) is equal to 1 tesla multiplied by 1 metre squared (1 Wb = 1 T m²)
State the equation for magnetic flux when the given area is perpendicular to the magnetic field.
The equation for magnetic flux when the given area is perpendicular to the magnetic field is: $Φ = B A$
Where:
- $B$ = magnetic flux density (T)
- $A$ = cross-sectional area (m²)
What does $θ$ represent in the equation $Φ = B A \cos θ$ ?
$θ$ represents the angle between the magnetic field and a normal (perpendicular line) to the area.
True or False?
Magnetic flux is zero when the magnetic field lines are parallel to the area.
True.
Magnetic flux is zero when the magnetic field lines are parallel to the area.
Define magnetic flux linkage.
Magnetic flux linkage is the product of the magnetic flux and the number of turns on the coil.
State the equation for magnetic flux linkage when the coil is at an angle of $θ$ to the field.
The equation for magnetic flux linkage is: $N Φ = N B A \cos θ$
Where:
- $N$ = number of turns of coil
- $B$ = magnetic flux density (T)
- $A$ = area of coil (m²)
- $θ$ = angle between the field and a normal to the area (°)
When is magnetic flux linkage at a maximum value?
Magnetic flux linkage is at a maximum value when the field and the area of the coil are perpendicular, i.e. when $θ = 90 °$ or $\cos θ = 1$
- the equation for calculating flux linkage $N Φ = N B A \cos θ$
- maximum flux linkage = $N B A$
True or False?
Magnetic flux is sometimes measured in units of Wb-turns.
False.
The unit of magnetic flux is the Weber (Wb).
Magnetic flux linkage is sometimes described in units of Wb-turns.
What three changes to a coil in a magnetic field can induce an e.m.f in it?
An e.m.f is induced in a coil when there is a change in:
- magnetic flux density, $B$
- area of coil within the field, $A$
- angle between the coil and field, $θ$
State Faraday's law of induction.
Faraday's law of induction states the magnitude of an induced e.m.f is directly proportional to the rate of change of magnetic flux linkage.
State the equation for Faraday's law of induction.
The equation for Faraday's law of induction is: $ε = - N \frac{∆ Φ}{∆ t}$
Where:
- $ε$ = induced e.m.f (V)
- $N$ = number of turns on coil
- $∆ Φ$ = change in magnetic flux (Wb)
- $∆ t$ = time interval (s)
When is a maximum e.m.f induced in a rectangular coil rotating in a magnetic field?
The induced e.m.f is at a maximum when the plane of the coil is parallel to the magnetic field lines.
The sides of the coil cut the field lines at the fastest rate at this position.
True or False?
No e.m.f is induced when a rotating rectangular coil is perpendicular to the magnetic field lines.
True.
No e.m.f is induced when a rotating rectangular coil is perpendicular to the magnetic field lines.
True or False?
Faraday's Law applies only to coils of wire.
False.
Faraday's Law applies to any conductor experiencing a change in magnetic flux linkage.
How does increasing the number of turns on a coil affect the magnitude of an induced e.m.f?
Increasing the number of turns in a coil increases the induced e.m.f for a given rate of change of magnetic flux.
Write an expression for the e.m.f. induced in a straight conductor moving perpendicularly across a magnetic field.
The e.m.f. induced in a straight conductor is: $ε = N \frac{∆ (B A)}{∆ t} = B (\frac{∆ A}{∆ t})$
Where:
- $N$ = 1 (for a straight conductor)
- $B$ = magnetic flux density (T)
- $∆ A$ = area swept out by conductor (m²)
- $∆ t$ = time interval (s)
Write an expression for the e.m.f. induced in a coil as it enters a perpendicular magnetic field.
The e.m.f. induced in a coil entering a perpendicular magnetic field is: $ε = N \frac{∆ (B A)}{∆ t} = N A (\frac{∆ B}{∆ t})$
Where:
- $N$ = number of turns on coil
- $A$ = area of coil (m²)
- $∆ B$ = change in magnetic flux density (T)
- $∆ t$ = time interval (s)
State Lenz's Law.
Lenz's law states the induced e.m.f in a coil or wire is such that it will oppose the change causing it.
What does the negative sign represent in the equation $ε = - N \frac{∆ Φ}{∆ t}$ ?
The negative sign represents the direction of the induced e.m.f. which will always oppose the change that produced it.
True or False?
Lenz's Law is a consequence of the principle of conservation of energy.
True.
Lenz's Law is a consequence of the principle of conservation of energy.
What happens to the direction of induced current when the direction of a magnet's motion is reversed?
When the direction of a magnet's motion is reversed, the direction of the induced current is also reversed.
What is self-induction?
Self-induction is the effect in which a change in the current tends to produce an induced e.m.f. which opposes the change of current in the same circuit
What is mutual induction?
Mutual induction is the effect in which a change in the current in one circuit tends to produce an induced e.m.f. which opposes the change of current in a neighbouring circuit
True or False?
The back e.m.f. in self-induction is directly proportional to the rate of current change.
False.
The back e.m.f. in self-induction is proportional to minus the rate of current change
What is a transformer?
A transformer is a device that changes high alternating voltage at low current to low alternating voltage at high current, and vice versa.
What is the role of the soft iron core in a transformer?
The role of the soft iron core in a transformer is to significantly increase the strength of the magnetic field from the primary to the secondary coil.
True or False?
In a step-up transformer, the primary coil has more turns than the secondary coil.
False.
In a step-up transformer, the secondary coil has more turns than the primary coil
What is an A.C. generator?
An A.C. generator is a device which converts energy from a mechanical store to an electrical store.
The output of an A.C. generator is alternating current.
What components make up a simple A.C. generator?
A simple A.C. generator consists of the following components:
1. a rectangular coil of wire rotating in a magnetic field
2. slip rings and brushes
What is the purpose of slip rings in an A.C. generator?
The purpose of slip rings in an A.C. generator is to provide a continuous connection between the rotating coil and the external circuit.
What is the equation for magnetic flux linkage in a rotating coil?
The equation for magnetic flux linkage in a rotating coil is: $N Φ = B A N \cos ω t$
Where:
- $B$ = magnetic flux density (T)
- $A$ = area of the coil (m²)
- $N$ = number of turns on the coil
- $ω$ = angular speed of the coil (rad s^-1)
- $t$ = time interval (s)
What is the equation for the induced e.m.f. in a rotating coil?
The equation for induced e.m.f. in a rotating coil is: $ε = B A N ω \sin ω t$
Where:
- $B$ = magnetic flux density (T)
- $A$ = area of the coil (m²)
- $N$ = number of turns on coil
- $ω$ = angular speed of the coil (rad s^-1)
- $t$ = time interval (s)
How does the induced e.m.f. vary with time in an A.C. generator?
The induced e.m.f. varies sinusoidally with time in an A.C. generator and is 90° out of phase with the flux linkage
The direction reverses every half rotation of the coil.
True or False?
In an A.C. generator, the maximum e.m.f is induced when the magnetic flux linkage through the coil is at a maximum.
False.
In an A.C. generator, when a maximum e.m.f is induced, the magnetic flux linkage is zero, but the change in flux linkage is at a maximum.
True or False?
No e.m.f is induced when a rotating rectangular coil is perpendicular to magnetic field lines.
True.
No e.m.f is induced when a rotating rectangular coil is perpendicular to magnetic field lines.
How can the size of the induced e.m.f. in a rotating coil be increased?
The size of the induced e.m.f in a rotating coil can be increased by increasing the frequency of rotation.
What is the effect of doubling the angular speed of a rotating coil on the induced e.m.f and frequency of rotation?
The effect of doubling the angular speed of a rotating coil is:
- the size of the induced e.m.f. doubles
- the frequency of the rotation doubles