CW Feb 25, 20194. What is electromagnetic induction?

How is this different from conventional current?

Explain what causes a current.

What is a current?

CW Feb 25, 20194. What is electromagnetic induction?

How is this different from conventional current? Conventional current is the flow of positive charge when in reality it is negatively charged electrons that flow.

Explain what causes a current. Current is caused by an electromotive force (EMF) which is a type of voltage. The size of the current depends on the resistance.

What is a current? A current is a flow of charge, this is usually an electron.

Learning Objectives

Show understanding that a conductor moving across a magnetic field or a changing magnetic field linking with a conductor can induce an e.m.f. in the conductor

State the factors affecting the magnitude of an induced e.m.f.

Knowledge organiserQuantity How do we find it? What does it mean?

Transformer equationVp / Vs = Np / Ns

Measure V using a voltmeter and count N

The ratio of the voltages of the primary and secondary coils is equal to the ratio of the

number of turns of the primary and secondary coils

Transformer efficiencyIpVp = IsVs

Measure I and V using an ammeter and a voltmeter

The electrical power (IV) of the primary coil is equal to the power of the secondary coil

if the efficiency is 100%

IGCSE Physics: 7. Electromagnetic effects

Any charge moving through a magnetic field experiences a force

If the charge is in a wire moving perpendicular to the magnetic field, the force is along the wire. The force does

work on each charge: voltage

If the movement of the wire is in the force of a rotating coil, then the two sides of the coil

move in opposite direction and the generated voltages add. This voltage generated will be

sinusoidal (AC)

When a changing voltage is applied to the primary coil, a changing magnetic field is generated. This magnetic field moves through the core and through

the secondary coil

To keep the torque (turning force) from reversing every half turn, a split ring commutator (and brushes)

is used which reverses the current at that point meaning the force continues in the same direction

The uniform magnetic field goes from north to south cutting through the coil

When a current-carrying conductor is placed in a magnetic field it

experiences a force: this is the motor effect

Key term Description

Conventional current

Always use this when dealing with motors and generators. The current moves from the positive terminal to the negative one: the opposite of electron flow

Solenoid A coil of current-carrying wire which generates a magnetic field in the shape of a bar magnet

Right hand screw rule

Used to determine both the direction of a magnetic field around a wire (thumb points in the direction fo I) or the poles of an electromagnet (fingers curl in direction of I)

Left hand rule Used to determine the force (F) of a wire undergoing the motor effect if the magnetic field direction (B) and the conventional current direction (I) are known

Motor A device which converts electrical energy into kinetic energy (and sound). It relies on the motor effect to provide a force on a current-carrying wire in a magnetic field

Split-Ring commutator

Allows a DC motor to keep moving in the same direction by ensuring the force continues to be in the same direction

Generator A device which converts kinetic energy into electrical energy. It relies on the generator effect to provide on a force on electrons (which does work) which is voltage

Transformer A device which steps-up (more turns on secondary) or steps-down (more turns on primary) the voltage to reduce the current (P = IV) to make electricity transfer more efficient

Efficiency How well a device transfers energy usefully. If all input energy goes to make useful energy the device is 100% efficient.

As a current-carrying coil is being cut by an external magnetic field a force is produced. As the

convectional current is in opposite directions the force on either end is in opposite directions

When a changing magnetic field moves through the secondary coil, an emf is generated. The sizes of this depends on the turn ratio of

the two coil

Transformers are used to step-up voltage and hence reduce current (P = IV) so less energy

is lost via heating when electrify is transferred through the National Grid

To determine the direction of the magnetic field, point your thumb in

the direction of the conventional current and your fingers curl in the

direction of the field lines

When a current is present in a conductor a circular magnetic field

is present.

If the conductor is coiled into a solenoid, the field has the same shape as that of a bar magnet

We can investigate the motor effect with this set-up. What happens when

the current and field are changed?The left hand rule for the motor effect:

FBI

The field lines above the wire are going in the same direction so add up to make a stronger

field. The field lines below cancel out to make a weaker field.

The force pushes the wire down away from the strong magnetic

field. The lines act like elastic band which don’t like to be squashed

A current-carrying coil experiences a turning force inside a uniform magnetic field. The motor effect is increased with increased

turns, current and magnetic fieldThe conventional current acts in opposite

direction on either side of the coil

We can determine the poles of the end of the electromagnetic using the right hand screw rule again: coil your fingers in the direction of the conventional current and your thumb

points to the north pole

When the conductor goes into the page we draw an “X”, when

coming out it has a “.”

Explain your decision.

Choose the odd one out.

Electromagnetic induction

Electro: ElectricityMagnetic: Magnetism

Induction: creation

“Electromagnetic or magnetic induction is the production of an electromotive

force across an electrical conductor in a changing magnetic field.”

What happens when the magnetic field is moved into the wire?

What happens when there is no relative movement?

What happens when the wire is moved in to the magnetic field?

What is the brightness of the lamp caused by?

Explain what you think is happening? (tick the ‘Field lines’ box)

What factors affect the brightness of the lamp?

https://phet.colorado.edu/sims/html/faradays-law/latest/faradays-law_en.html

Factors that affect the magnitude of an induced emf:

The strength of the magnetic

The number of turns in the coil

The speed of the magnet

The area of the coil

Describe how each factors affects the magnitude of the induced emf.

Explain why these factors affect the induced emf.

Write down these factors.

Factors that affect the magnitude of an induced emf:

The strength of the magnetic (greater)

The number of turns in the coil (greater)

The speed of the magnet (greater)

The area of the coil (greater)

This is because the larger and the faster the change in field lines being cut of the coil, the greater the induced emf.

What happens when the magnet is reveresed and then brought back in to the coil?

Explain your observations?

What happens when the magnet is moved back out the coil?

Learning Objectives

Show understanding that a conductor moving across a magnetic field or a changing magnetic field linking with a conductor can induce an e.m.f. in the conductor

State the factors affecting the magnitude of an induced e.m.f.

Knowledge organiserQuantity How do we find it? What does it mean?

Transformer equationVp / Vs = Np / Ns

Measure V using a voltmeter and count N

The ratio of the voltages of the primary and secondary coils is equal to the ratio of the

number of turns of the primary and secondary coils

Transformer efficiencyIpVp = IsVs

Measure I and V using an ammeter and a voltmeter

The electrical power (IV) of the primary coil is equal to the power of the secondary coil

if the efficiency is 100%

IGCSE Physics: 7. Electromagnetic effects

Any charge moving through a magnetic field experiences a force

If the charge is in a wire moving perpendicular to the magnetic field, the force is along the wire. The force does

work on each charge: voltage

If the movement of the wire is in the force of a rotating coil, then the two sides of the coil

move in opposite direction and the generated voltages add. This voltage generated will be

sinusoidal (AC)

When a changing voltage is applied to the primary coil, a changing magnetic field is generated. This magnetic field moves through the core and through

the secondary coil

To keep the torque (turning force) from reversing every half turn, a split ring commutator (and brushes)

is used which reverses the current at that point meaning the force continues in the same direction

The uniform magnetic field goes from north to south cutting through the coil

When a current-carrying conductor is placed in a magnetic field it

experiences a force: this is the motor effect

Key term Description

Conventional current

Always use this when dealing with motors and generators. The current moves from the positive terminal to the negative one: the opposite of electron flow

Solenoid A coil of current-carrying wire which generates a magnetic field in the shape of a bar magnet

Right hand screw rule

Used to determine both the direction of a magnetic field around a wire (thumb points in the direction fo I) or the poles of an electromagnet (fingers curl in direction of I)

Left hand rule Used to determine the force (F) of a wire undergoing the motor effect if the magnetic field direction (B) and the conventional current direction (I) are known

Motor A device which converts electrical energy into kinetic energy (and sound). It relies on the motor effect to provide a force on a current-carrying wire in a magnetic field

Split-Ring commutator

Allows a DC motor to keep moving in the same direction by ensuring the force continues to be in the same direction

Generator A device which converts kinetic energy into electrical energy. It relies on the generator effect to provide on a force on electrons (which does work) which is voltage

Transformer A device which steps-up (more turns on secondary) or steps-down (more turns on primary) the voltage to reduce the current (P = IV) to make electricity transfer more efficient

Efficiency How well a device transfers energy usefully. If all input energy goes to make useful energy the device is 100% efficient.

As a current-carrying coil is being cut by an external magnetic field a force is produced. As the

convectional current is in opposite directions the force on either end is in opposite directions

When a changing magnetic field moves through the secondary coil, an emf is generated. The sizes of this depends on the turn ratio of

the two coil

Transformers are used to step-up voltage and hence reduce current (P = IV) so less energy

is lost via heating when electrify is transferred through the National Grid

To determine the direction of the magnetic field, point your thumb in

the direction of the conventional current and your fingers curl in the

direction of the field lines

When a current is present in a conductor a circular magnetic field

is present.

If the conductor is coiled into a solenoid, the field has the same shape as that of a bar magnet

We can investigate the motor effect with this set-up. What happens when

the current and field are changed?The left hand rule for the motor effect:

FBI

The field lines above the wire are going in the same direction so add up to make a stronger

field. The field lines below cancel out to make a weaker field.

The force pushes the wire down away from the strong magnetic

field. The lines act like elastic band which don’t like to be squashed

A current-carrying coil experiences a turning force inside a uniform magnetic field. The motor effect is increased with increased

turns, current and magnetic fieldThe conventional current acts in opposite

direction on either side of the coil

We can determine the poles of the end of the electromagnetic using the right hand screw rule again: coil your fingers in the direction of the conventional current and your thumb

points to the north pole

When the conductor goes into the page we draw an “X”, when

coming out it has a “.”

There is a voltage because field lines are cut

Voltage is greater More field lines are cut per second.

Lower

Greater

Opposite direction

What is electromagnetic induction?

Write down your best answer to this question.

Include any key words or diagrams you think are

necessary