6.20 know and use the relationship: input power = output power

V_pI_p = V_sI_s

For 100% efficiency

V = Voltage

I = Current

p = primary

s = secondary

To find one value rearrange the equation (i.e. divide by something on both sides to leave a value on the other)

(V_pI_p) ÷ I_s  = V_s

Always use A for current, not kA 

Always use V for voltage, not kV

6.19 know and use the relationship between input (primary) and output (secondary) voltages and the turns ratio for a transformer.

V = Voltage

n = Number of turns

p = primary

s = secondary

Input Voltage / Output Voltage = Number of turns of primary / number of turns on secondary

Always use volts and not kV

6.18 explain the use of step-up and step-down transformers in the large-scale generation and transmission of electrical energy

The voltage produced by power stations is too low to be transmitted efficiently. Power = VI (voltage x current) so for a given amount of power the current must be higher to accommodate for the lower voltage and current causes the wires to heat up. 

1. A step up transformer is used to boost the voltage, thus lowering the current, before it's transmitted.
2. Step down transformers are used at the end of the journey to lower the voltage to 230V and a much higher current. 

6.17 describe the structure of a transformer, and understand that a transformer changes the size of an alternating voltage by having different numbers of turns on the input and output sides

Transformer:

On the left we have the primary coil, then a soft iron core and then a secondary coil.

The job of the transformer is to change the size of the voltage of an alternating current.
They do this by having a different number of coils on the primary coil and secondary coil.

When an a.c. current is applied to the primary coil the soft iron core magnetises and demagnetises quickly. This induces a current an a.c. current in the secondary coil.

A step-up transformer has less coils on the primary coil than it does on the secondary so it steps up the voltage.
A step-down transformer has more coils on the primary coil than on the secondary so it steps down the voltage.

6.11 understand that there is a force on a charged particle when it moves in a magnetic field as long as its motion is not parallel to the field

When an electron, proton or any other charged particle moves through a magnetic field it experiences a force as long it's not moving parallel to the field lines.

6.9 describe the construction of electromagnets

A wire is wrapped around a soft core (usually iron). When this wire has a current flowing through it the core becomes magnetised thus making an electromagnet.

6.10 sketch and recognise magnetic field patterns for a straight wire, a flat circular coil and a solenoid when each is carrying a current

Magnetic Field Around A Straight Wire

Magnetic Field around a Flat Circular Coil

Magnetic Field around a Solenoid

Ignore the B= thing up top but do take note of where the current goes in and out represented by "I"

Using LHR in any question like this may be useful