#p3.3

[gr00vycat]

16.2.16 // 7:53PM [10/100 days of productivity] Been doing some P3.3 revision tasks that my teacher gave us (not compulsory but I'm DETERMINED to get an A* in my P3 re mock). Also artificial lighting is ugly.

[iamrevisinghonest-gcse]

Transformers

If an electrical conductor "cuts" through a magnetic field, a potential difference is induced across the ends of the conductor.

If a magnet is moved into a coil of wire, a potential difference is induced across the ends of the coil.

The transformer works as follows:

An alternating current flowing through the primary coil induces a changing magnetic field in the iron core

This magnetic field is also induced in the secondary coil

This induces an alternating potential difference across the ends of the secondary coil.

In a step-up transformer, the potential difference across the secondary coil is greater than that across the primary coil.

In a step-down transformer, the potential difference across the secondary coil is less than that across the primary coil.

The equation for calculating the potential difference across the primary or secondary coils of a transformer is:

Vp ÷ Ip = Vs ÷ Is

Vp = potential difference across the primary coil (volts, V)

Ip = potential difference across the secondary coil (volts, V)

np = number of turns on the primary coil

ns = number of turns on the secondary coil

If a transformer is assumed to be 100% efficient, the electrical power output equals the electrical power input.

The equation for calculating the electrical power output is:

Vp x Ip = Vs x Is

Vp = potential difference across the primary coil (volts, V)

Ip = current in the primary coil (amperes, amps, A)

Vs = potential difference across the secondary coil (volts, V)

Is = current in the secondary coil (amperes, amps, A)

Switch mode transformers are much lighter and smaller than traditional transformers and operate at a high frequency (usually from around 50 kHz to 200 kHz). They are used as mobile phone chargers. They do not used much power when they are switched on if no load is applied.

[iamrevisinghonest-gcse]

The Motor Effect

When an electric current flows through a wire, it produces a magnetic field around the wire.

The motor effect is when magnetic fields produced by electric currents are used to make things move. It has many appliances, such as the electric motor.

The size of the force can be increased by:

Increasing the strength of the magnetic field

Increasing the size of the current.

The direction of the force can be reversed by:

Reversing the direction of the current

Reversing the direction of the magnetic field.

[iamrevisinghonest-gcse]

Keeping Things Moving

Electric currents produce magnetic fields. Forces that are produced in magnetic fields can be used to make things move. This is called the motor effect. Appliances such as the electric motor use the motor effect to create movement.

There are many appliances that do not use 230 volts mains electricity. We use transformers to provide the required potential difference.

You should be able to use your skills, knowledge and understanding to:

Interpret diagrams of electromagnetic appliances in order to explain how they work

Compare different types of transformers and their uses in different applications.

Practical work to develop your skills and understanding:

Placing a foil strip with a current flowing through it into a strong magnetic field

Building a motor

Making a loudspeaker

Making a transformer using C cores and insulated wire

Demonstrating a transformer to show the difference between using d.c. and a.c.