The generator effect and transformers

When can a voltage be induced?

When there is motion between a magnetic field and a conductor

When can a current be induced?

If the conductor is part of a complete circuit

How to increase the size of the induced voltage 3

• increase the speed of movement

• Increase the magnetic field strength

• Increase the number of turns on the coil

Describe how generators work 5

• the permanent magnets provide a uniform magnetic field in the generator

• The conductor is made to turn in a way that it cuts the magnetic field lines

• As the coil is forced to rotate in the magnetic field, a voltage is induced in the wire

• The induced voltage/current changes direction every half turn

• Slip rings and brushes ensure the contacts do not swap every half turn so maintain a constant contact

What does a step-up transformer have?

• more turns on the secondary coil

• Increases voltage

• Decreases current

What does a step-down transformer have?

• fewer turns on the secondary coil

• Decreases voltage

• Increases current

Describe the structure of a transformer 3

• 2 coils of wire

• The coils are linked by a soft iron core

• (Mention the relative number of each turns on each coil)

Why do transformers need an alternating current?

• to provide an alternating magnetic field In the core

• Which then cuts the conductor of the secondary core

• Otherwise no voltage will be induced

Describe how transformers work 5

• An alternating voltage provides an alternating current around the primary coil

• This produces an alternating magnetic field

• This induced an alternating magnetic field in the iron core

• The alternating magnetic field of the iron core induces an alternating voltage across the secondary coil

• This creates an alternating current in the secondary coil if it is in a circuit.

Why are voltages stepped up?

To increase efficiency during transmission

Why are voltages stepped down?

To be made safe for use

Why do EVs slow down quicker during regenerative braking?

• the chemical store of the battery is increased

• Energy is conserved so the kinetic store of the car must decrease.

Explain how the transmission of electrical power is made more efficient by using step-up and step-down transformers.

• the cables for transmission act as a resistor

• Ohm’s law V=IR

• Therefore if P=IV then P=I² R

• Power loss is proportional to the current squared

• As P=IV if the current increases, the voltage decreases because P is constant

• Higher currents dissipate more energy to the surroundings

• Therefore we increase the voltage to decrease the current using a step-up transformer

• This reduces wasted energy

• Step-down transformers are used downstream to lower voltage and increase current for domestic use

• Transformers can be made more efficient using low resistance coils and a soft iron core

• Energy wastage can be reduced by using low resistance wires.