EM Induction

What is electromagnetic induction?

Electromagnetic induction is the production of an induced potential difference (and therefore a current if the circuit is complete) when there is relative movement between a magnet and a conductor.

How can an electric current be produced by electromagnetic induction in the laboratory?

Move a magnet relative to a coil of wire, or move the coil relative to the magnet. This changes the magnetic field through the coil and induces a potential difference.

What happens if the magnet and conductor are stationary relative to each other?

No potential difference is induced because there is no change in the magnetic field through the conductor.

What factors affect the size of an induced potential difference?

The speed of relative movement, the strength of the magnetic field, and the number of turns on the coil. Increasing any of these increases the induced potential difference.

What determines the direction of an induced potential difference?

The direction of the relative movement and the direction of the magnetic field determine the direction of the induced potential difference.

What does the induced magnetic field do according to Lenz's law?

The magnetic field produced by the induced current opposes the original change that caused the induction.

How does electromagnetic induction generate electricity on a large scale?

Generators use electromagnetic induction. A coil and magnetic field move relative to each other, inducing a potential difference and current in the coil.

What is an alternator?

An alternator is a generator that produces alternating current (a.c.), where the current repeatedly changes direction.

How does an alternator generate a.c.?

A coil rotates in a magnetic field, causing the induced potential difference and current to repeatedly reverse direction.

What is a dynamo?

A dynamo is a generator that produces direct current (d.c.).

How does a dynamo produce d.c.?

Electromagnetic induction produces a changing potential difference, but a split-ring commutator reverses the connections every half-turn so the current flows in one direction.

How does a microphone work?

A microphone converts pressure variations in sound waves into variations in electrical current. The sound causes a diaphragm to vibrate, producing corresponding variations in the electrical signal.

How does a loudspeaker work?

A loudspeaker converts variations in electrical current into pressure variations in air. The varying current causes a coil in a magnetic field to move, making the speaker cone vibrate.

How do headphones work?

Headphones use the reverse effect of a microphone: variations in electrical current cause a diaphragm to vibrate, producing sound waves.

How can an alternating current in one circuit induce a current in another circuit?

An alternating current produces a changing magnetic field. This changing magnetic field passes through a nearby coil and induces a potential difference and current in the second circuit.

What is a transformer?

A transformer is a device that uses electromagnetic induction to change the size of an alternating potential difference.

Can a transformer work with direct current (d.c.)?

No. A transformer requires a changing magnetic field, so it operates with alternating current (a.c.).

What is the primary coil of a transformer?

The primary coil is the coil connected to the input a.c. supply.

What is the secondary coil of a transformer?

The secondary coil is the coil from which the transformed a.c. output is taken.

What does a step-up transformer do?

A step-up transformer increases the output potential difference.

What does a step-down transformer do?

A step-down transformer decreases the output potential difference.

What determines whether a transformer steps voltage up or down?

The relative numbers of turns on the primary and secondary coils. More turns on the secondary gives a step-up transformer; fewer turns gives a step-down transformer.

What is the transformer turns ratio equation?

Vp/Vs = Np/Ns

What does Vp represent in the transformer equation?

Vp is the potential difference across the primary coil, measured in volts (V).

What does Vs represent in the transformer equation?

Vs is the potential difference across the secondary coil, measured in volts (V).

What does Np represent in the transformer equation?

Np is the number of turns on the primary coil.

What does Ns represent in the transformer equation?

Ns is the number of turns on the secondary coil.

A transformer has 200 primary turns and 1000 secondary turns. Is it step-up or step-down?

It is a step-up transformer because the secondary coil has more turns than the primary coil.

A transformer has 1000 primary turns and 200 secondary turns. Is it step-up or step-down?

It is a step-down transformer because the secondary coil has fewer turns than the primary coil.

Why is electrical energy transmitted at high voltage in the national grid?

For a given power, increasing the voltage reduces the current. Lower current means less energy is dissipated as thermal energy in the transmission cables, improving efficiency.

Why does reducing current reduce heat loss in transmission cables?

The power dissipated in the cables is related to P = I²R. A smaller current produces a much smaller power loss because current is squared.

Where are step-up transformers used in the national grid?

Step-up transformers are used near power stations to increase the voltage before electricity is transmitted over long distances.

Where are step-down transformers used in the national grid?

Step-down transformers are used near homes and businesses to reduce the voltage to safer levels suitable for domestic and local use.

What is the transformer power equation for a transformer with 100% efficiency?

Vp × Ip = Vs × Is

What does Ip represent in the transformer power equation?

Ip is the current in the primary coil, measured in amperes (A).

What does Is represent in the transformer power equation?

Is is the current in the secondary coil, measured in amperes (A).

What does 100% transformer efficiency mean?

It means the power transferred to the secondary coil equals the power supplied to the primary coil, with no energy losses.

How does a step-up transformer affect current in an ideal transformer?

If the voltage is increased, the current decreases so that power remains constant.

How does a step-down transformer affect current in an ideal transformer?

If the voltage is decreased, the current increases so that power remains constant.

Why are transformers important in the national grid?

They allow voltage to be increased for efficient long-distance transmission and then reduced to suitable voltages for domestic and local use.

What is the main advantage of high-voltage transmission?

High voltage allows the same power to be transmitted using a smaller current, reducing heating losses and improving transmission efficiency.

What equations are used to explain high-voltage power transmission?

P = E/t, P = IV, Vp/Vs = Np/Ns, and VpIp = VsIs.