6.20 Know and use the relationship: input power = output power for 100% efficiency

VPIP =VSIS


Voltage primary x current primary = voltage secondary x current secondary

Voltage in volts (v)
Current in amps (A)

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

^Vp/_Vs = ^Np/<sub>Ns
Voltage primary ÷ voltage secondary = Number of coils in primary ÷ number of coils in secondary

Number of coils has no units
Voltage is in volts</sub>

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

Figure 1

The structure of a step up (above) transformer and a step down (below) transformer can be seen in figure 1. As the voltage decreases, current increases, and vice versa. The transformer changes the size of the voltage by having a different number of primary and secondary coils. If there are more secondary coils, it is a step up transformer and will increase the voltage. If there are more primary coils, it is a step down transformer and will decrease the voltage. (Also has an iron core. That's important.)

6.16 Describe the generation of electricity by the rotation of a magnet within a coil of wire and of a coil of wire within a magnetic field and describe the factors which affect the size of the induced voltage

Most helpful video I've seen in a really long time, which hopefully works....

• Movement of magnet produces electromagnetic force 
• Movement + magnetism = current
• 2 slip rings make contact with 2 brushes with copper or carbon connected to an external circuit
• Coil rotates, one half upwards, other downwards
• This produces current in 1 direction
• As continues rotating, half moving upwards moves downwards, vice versa. This constant change results in AC
• Replacing slip rings with split ring produces DC because it reverses current when it is naturally going to reverse so it produces current in only one direction

More diagrams here

6.15 Understand that a voltage is induced in a conductor or a coil when it moves through a magnetic field or when a magnetic field changes through it and describe the factors which affect the size of the induced voltage

Voltage is induced in a conductor (typically a wire) or coil when it moves through a magnetic field (i.e when a wire is moved back and forth in a magnetic field) or when a magnet is moved continuously in and out of a coil of wire. 

GOLDEN RULE:
Field + Motion = Current induced

If you:

• increase magnetic field strength
• increase speed of magnet going in/out of coil of wire
• increase number of coils of wire

then more current will be induced :)

Let's talk about the magnet and the coil for a second. How does it work? 

• Magnet moves into the coil (let's say S side first)
• Electrons don't like change, so they form a S pole to repel the south pole
• Magnet moves out
• But then the electrons miss the south and they want it back (they don't like change) so they create a N pole to attract the south pole back again
• Magnet moves in
• This is repeated, inducing an alternating current (AC)
• (this is the basic idea for a generator)

WARNING: DO NOT USE THE WORD "CREATE" WHEN REFERRING TO CURRENT OR VOLTAGE. YOU WILL GET MARKED DOWN / MARK WILL NOT BE GIVEN.