6.20 know and use the relationship between input power and output power

VPIP =VSIS

(for 100% efficiency)

6.19 know and use the relationship between input (primary) and output (secondary) voltages and the turns ratio for a transformerinput (primary) voltage = primary turns output (secondary) voltage secondary turns

primary voltage / secondary voltage = turns on primary / turns on secondary

^Vp/_Vs = ^Np/_Ns

_{NOTE: 'N' stands for number of coils}

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

Transformers are used in the National Grid. This is because the wires are long there is more resistance, so a high current will cause a lot of heat which is dangerous and looses a lot of energy (it is not energy efficient). When electricity leaves a power plant/generator, a step up transformer is used, this increased the voltage but decreases the current. When electricity reaches nearby the areas it is to be used, for example factories and edge of towns, it is stepped down. Once the wires reach a home or business it is stepped down once more (to 230v) to make it useful in appliances that we use.

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

Transformers are used to change the current and voltage of electricity.

How they work...

A wire carrying a current is wrapped round one side of the transformer, another wire is wrapped round the other. There will be the same amount of power on both sides, but one will have a higher voltage and lower current the other a lower voltage and a higher current.

The transformer is made of iron, this is because it is a soft metal and can be turned on and off as a magnet (it is a magnetically soft material): the current from the first wire induces a magnetic field in the transformer, this then induces a current in the second wire.

More coils causes more higher voltage (and lower current). So if the second side has more turns of wire wrapped round the transformer it will step the voltage up (step up transformer.) If the second side has less turns, the voltage will be stepped down and current increased (step down transformer).

If your having trouble getting to grips with this (it is very hard!), the animation at the bottom of this page may help... http://www.bbc.co.uk/schools/gcsebitesize/science/edexcel/generation_transmission_electricity/transmitting_electricityrev2.shtml

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

If you rotate a magnet in a coil of wire, a current will be induced. Also, if you rotate coil of wire in a magnetic field a current will be induced.

Factors that increase the electricity induced...
- Strength of magnetic field
- Number of coils in wire
- Speed of rotations

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

- If you more a wire back and forth in a magnetic field or through a coil (solenoid), a voltage will be induced.
- Increasing the magnetic field strength, quickening the speed your moving the wire or increasing the number of coils, will all increase the voltage.

6.14 describe how the force on a current-carrying conductor in a magnetic field increases with the strength of the field and with the current.

Lets say, for example, you have a wire in a magnetic field. If you increase the current there will be more force on the wire; if you increase the strength of the magnetic field there will be fore force on the wire, meaning more force on the conductor.

6.13 use the left hand rule to predict the direction of the resulting force when a wire carries a current perpendicular to a magnetic field

The magnetic field finger is pointing south.

The current finger is pointing negative.

6.12 understand that a force is exerted on a current-carrying wire in a magnetic field, and how this effect is applied in simple d.c. electric motors and loudspeakers

If a current through a piece of wire is held at right angles to a magnetic field, the wire will move (as a force is created)

When a current flowing through a wire is put through a magnet, the magnetic field lines overlap. 

in some places, the direction of the fields are the same, and the magnetic field is stronger. in other places, the direction of the fields are in opposite directions, so the magnetic field is weaker. 

the wire is pushed from the strong part of the field to the weak part (the magnetic field lines don’t like being squished together) 

electric motors

the magnets on the two sides of the coil are at different directions. One side feels the force pushing it downwards, whilst the other is being pushed upwards, so the coil rotates. 

the direction current on each side of the coil is switched when the coil is vertical by the commutator, so the forces acting on each side is switched and the rotation direction is maintained 

to increase rate of motor turns:
- increase the number of turns or loops of wire (to make a coil)
- increase the strength of the magnetic field
- increase current flowing through the loop of wire 

cr:phychembi.tumblr.com

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

If a charged particle moves into a magnetic field, it experiences a force pulling it in the direction of the field.

When a charged particle, that is parallel to the magnetic field line, entres the magnetic fiend line, it will not experience a force. This is because the charged particle is already going in the direction of the magnetic field.

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

Straight wire

A magnetic field around a straight wire is a series of circles around the wire

Flat circular coil

A magnetic field around a flat circular coil is pretty much the same as a single wire, only there are two

Solenoid

A magnetic field around a solenoid is similar to a magnetic field around a bar magnet.

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

6.9 describe the construction of electromagnets

An electromagnet is a solenoid with an iron core inserted into it. If a current flows in the coil, a magnetic field is generated. Therefore, to make an electromagnet all you need to do is wrap a piece of wire around a magnetically soft material. When a current is induced in a wire, the magnetically soft material becomes magnetised. The coil is knows as a solenoid.

6.8 understand that an electric current in a conductor produces a magnetic field round it

If you run an electric current through any conductor of electricity (for example, a wire), a magnetic field will be produced around the conductor. However, this field is quite weak ( it is also in a circular shape).



If it helps, use the 'right hand rule' to find which direction the magnetic field runs.