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>

6.18 Explain the use of step-up and step-down transformers in the largescale generation and transmission of electrical energy

Transformers in the national grid are used to stop the wires from overheating - a very high current flowing through very long wires would produce a lot of heat, because the wires have some resistance.

• Step up transformers increase the voltage, decrease the current to stop energy waste through heat when passing through long wires

• In households, wires are shorter so there's less heat wasted, so step down transformer decreases voltage and increases current to make it more useful to us. 

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.

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.

Two things that increase force on the wire (which is the "current carrying conductor") are:

• increasing strength of magnetic field
• increasing amount of current flowing

:)

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

Hello world. This is the left hand rule, and it can be used to determine the direction of force, magnetic field and / or current when a wire carries a current perpendicular  to the magnetic field. (figure 1)

Figure 1

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

A force is exerted on a current carrying wire - you see this if you put it between two ends of a U shaped magnet with a current through it. Depending on the direction of the current, it will either move up or down. 

In speakers (link to BBC bitesize), the current is constantly changing direction. This means the poles of the electromagnet change, and so the wire varies between moving up and down - the current varies with the music. The electromagnet moves back and forth, creating vibrations, generating sound waves whose frequency changes with the frequency of the current.

In simple DC motors (link to BBC bitesize) , as we know, the wire experiences a force when it is within a magnetic field, and it moves. The current needs to be reversed every half term, which is done by a split ring commutator, to keep it spinning. The momentum it gains after it has started spinning helps keep it going, too.

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

There is a force acting on the charged particle when it moves in the magnetic field unless its motion is parallel to it, in which case there isn't really, because it is already moving in the direction the magnetic field "wants" it to.

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
Basically little circles around the wire. Direction determined with right hand grip. (fig 1)

Figure 1

Solenoid (coil of wire)

Sort of like a regular magnetic field...in a tube... (fig 2) Direction can be found with right hand grip.

Figure 2

Flat coil

Like a regular wire x2 with a line in the middle. Again, determined with right hand grip. (fig 3)

Figure 3

6.9 Describe the construction of electromagnets

A coil of wire with a soft iron core and a current running through it will induce a magnetic field.

WARNING: do not use the word "create" for magnetic field, you will not get the mark :(

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

An electric current in a conductor, such as a wire, produces a magnetic field around it. Fairly self explanatory point. (:

6.7 Describe how to use two permanent magnets to produce a uniform magnetic field pattern.

Hold two opposite poles very close to each other so they attract. This will make a uniform magnetic field :) kind of as if they were one magnet

6.6 Describe experiments to investigate the magnetic field pattern for a permanent bar magnet and that between two bar magnets

1. 

• Take a piece of paper and a compass
• Place a magnet in the middle of the paper
• Slowly move the compass around the magnet. Draw on the paper where the arrow points each time
• Repeat until shape of magnetic field forms
• MULTIPLE COMPASSES MAY BE USED

2.

• Take a sheet of paper, iron filings and a magnet
• Place magnet under paper
• Carefully pour iron filings onto paper
• Magnetic field shape should form
• Yay

6.5 Understand that magnetism is induced in some materials when they are placed in a magnetic field

Some materials can become magnetic when they are placed in a magnetic field as it aligns all the domains inside, forming poles. Can happen to Fe, Co and Ni.

6.4 Understand the term ‘magnetic field line’

Magnetic field lines show the direction of the magnetic field (north to south). Field is 3D, lines give an idea. MUST NEVER TOUCH WHEN DRAWING. Add arrows :)

6.3 Describe the properties of magnetically hard and soft materials

Soft magnetic materials

• loses its magnetism almost as soon as it leaves the magnetic field
• can be magnetized / demagnetized
• i.e. soft iron core
• i.e. in electromagnets

Hard magnetic materials

• retains its magnetic properties

6.2 Understand that magnets repel and attract other magnets and attract magnetic substances

Magnets attract / repel other magnets depending on their poles and attract magnetic substances, which consist of:

• iron (Fe)
• nickel (Ni)
• cobalt (Co)

and any alloys that contain those metals.

6.1 Use the following units: ampere (A), volt (V), watt (W).

Amp (A) - current

Volt (V) - voltage (surprise!)

Watt (W) - power

5.8 Describe the arrangement and motion of particles in solids, liquids and gases

Solid

• Close
• Vibrating
• Little energy
• No bumping other than vibration

Liquid

• Sort of close, with some gaps
• Some movement
• Some energy
• Particles bounce / collide with each other, creating some gaps

Gas

• Far apart
• Lots of energy
• Lots of movement
• Collisions that spread particles often
• Collisions / bumping creates space between particles

5.7 Understand the changes that occur when a solid melts to form a liquid, and when a liquid evaporates or boils to form a gas

Solid to liquid

• More energy
• Particles move faster
• Bump more frequently
• Further apart
• Brush past each other

Liquid to gas

• Much more energy
• Particles move much faster
• Bump more frequently
• Very far apart
• Hardly touch (except when bumping..tee hee)

*mind blown*

1.36 Understand that: the universe is a large collection of billions of galaxies, a galaxy is a large collection of billions of stars, our solar system is in the Milky Way galaxy.

So basically:

• the universe is a large collection of billions of galaxies 

• a galaxy is a large collection of billions of stars

• our solar system is in the Milky Way galaxy. 

1.35 Use the relationship between orbital speed, orbital radius and time period

0. 
   
1. orbital speed = 2 x π x r / T
2. ( 2 x pi x radius ÷ time)

Orbital speed in m/s

Radius in m

Time in sec

1.34 Describe the differences in the orbits of comets, moons and planets

• All have elliptical orbits
• Moons orbit around planets
• Comets orbit stars
• Planets orbit stars
• Comets have elongated orbits

Figure 1: A comet's orbit

The comet will be moving fastest when it is further away from the star (right end of the ellipse)

1.33 Explain that gravitational force causes the following..

...

• causes moons to orbit planets
• causes the planets to orbit the sun
• causes artificial satellites to orbit the Earth 
• causes comets to orbit the sun 

If an object is within a planet's gravitational field, it will orbit around it in an orbit. These are not perfect, circular orbits for planets and satellites. Comets have elliptical orbits.

1.32 Understand gravitational field strength, g, and recall that it is different on other planets and the moon from that on the Earth

All objects have an attracting force. The Earth attracts you and you attract the Earth. The larger the object, the larger the attracting force. Planets are large enough to have a gravitational field, and we measure this and call it g. 

On earth, g is approximately 10 n/kg

On other planets, it varies with their mass.