Google
Web
Revision-GCSE

Physics

Is physics the hardest science? Discuss on the forums... Personally, I think it is, so let's start with that topic, to give you lot longer to revise it... This is from the Year 10 Physics module; however, it's the stuff that you need to know in Year 11.

Electricity

Key Words... learn these and you'll never go wrong...
Current (amps) The flow of electrons round a circuit.
Voltage (volts) The "driving force" that pushes the current around the circuit.
Resistance (ohms) Anything that slows down the flow.

The exam board love those "three formula" and this is an example of one:

Resistance = Voltage ÷ Current or
Voltage = Resistance x Current or
Current = Voltage ÷ Resistance

Basically that means: A greater Voltage allows more Current to flow, while a greater Resistance allows less Current to flow.

Another way of putting it: The current through a resistor (at a constant temperature) is proportional to the voltage across the resistor.

Key circuit symbols...Exams love these, especially the obscure ones. Draw them all from memory...


Voltmeter


Ammeter

Filament Lamp

Resistor

Cell

Battery

LDR

Thermistor

Fuse

Diode

Variable Resistor
LED

Switch open

Switch closed
Motor
Loudspeaker

Resistance is futile (look up "futile" for your english exam)...

LDR - As the light intensity increases, the resistance drops.

Thermistor - As the temperature increases, the resistance drops. (However, there are thermistors that work the opposite way round.

Here's how I remember it: Working in the cold, dark of the night with LDRs and Thermistors, you're pretty much screwed...

Three graphs your life wouldn't be complete with... In other words learn them for the exam...

The current through a resistor at a constant temperature will be proportional to the voltage running through it. As the temperature of a filament lamp increases, the resistance increases. A diode only allows the current to flow in one direction. In the other direction the resistance is infinity.

Resistance and gradient: The steeper the graph line, the lower the resistance. Pretty obvious if you think about it.

And finally...

Remember a voltmeter goes in parallel with the component you're measuring, while a ammeter goes in series.

Voltmeters measure voltage (p.d. for potential difference, if you're posh).

Ammeters measure the current, in amps (amps are symbolised as "I" for some reason...)

And that's the first horrible bit of electricity done! :)

Go to top!


Creating Electricity

Ever wondered where that stuff powering your computer comes from? Well, electricity's just the most useful form of energy, as it can be transferred to any of the other forms easily. And as energy cannot be created or destroyed, electricity needs to be made by converting one of the other forms...

If you move a magnet into a coil of wire that is part of a complete circuit, potential difference (voltage) is created between the ends of the wires. This leads to a current being created (or induced to use the proper terminology).

By cutting through the magnetic fields in the opposite direction, the current in reversed. This is how we get a.c. electricity (alternate current).

A more sophisticated way though is to create electricity by rotating a coil of wires in a magnetic field or rotating a magnet in a coil of wires. This is what happens in all electricity generators (except nuclear). Their energy is converted to kinetic, which rotates the magnet to produce electricity.

The size of the current increases by:

  • Increasing the speed of movement (moving the magnet faster).
  • Increasing the strength of the magnetic field (stronger magnet).
  • Increasing the number of turns on the coil.
  • Increasing the area of the wire.

Go to top!


Renewable and Non-renewable

So now we know a little bit about electricity, how exactly do generators work?

First, check you know what the key words are:

Renewable

1. They will never run out ...so long as the sun keeps shining...

2. They are much less harmful to to the environment.

3. Only main trouble is that they don't produce much energy and are often unreliable.

Non-renewable

1. These ones will run out.

2. They all do a lot of damage to the environment.

3. But they do produce loads of energy.

Which are which? C'mon, this is all really basic stuff!

Non-renewable
Renewable
Coal
Hydroelectric
Oil
Solar
Nuclear
Wind
Natural Gas
Tidal
Wave
Geothermal
Biomass (Wood)

Advantages and Disadvantages

Energy Source
Advantages
Disadvantages
 Fossil Fuels (coal, oil, gas) Cheap. Reliable. Meets demand. Pollution - leading to Global Warming, Acid Rain. Will run out.
 Nuclear Produces loads of energy.

Dangerous. Nuclear waste disposal problems. 

 Geothermal Cheap. No atmospheric pollution. Can meet demand.  Finding a site. Rocks will eventually cool.
 Hydroelectric No atmospheric pollution. Meets demand. Renewable.

Location. Expensive to build. Environmental problems. 

 Wind

No atmospheric pollution. Renewable. 

Unreliable. Produces dilute energy. Some people find them "visually polluting". 
 Solar No atmospheric pollution. Renewable.  Unreliable. Expensive to build.
 Tidal No pollution. Renewable.  Site. Can't meet demand. Expensive to build.
 Wave No atmospheric pollution. Renewable. 

Dilute energy. Can cause environmental problems.

Um, yeah. Like though most renewables have high initial costs, they don't cost much to run. Only trouble is most don't produce a lot of electric, as it's dilute energy...and so can't meet demand.

Costs for running a nuclear plant are low, but setting up, decommissioning and disposing of waste make costs fairly high... (For more on nuclear reactions, click here.)

Besides nuclear and solar energy, the various energy sources are used to spin the turbines, which in turn spin the generator. The generator is the magnet that spins inside the coil of wire (or vice versa), inducing a current.

How A.C. works

A.C. stands for alternating current. As you rotate a coil of wire inside the magnetic fields, the direction of the current changes. When the wire cuts through the north end of the magnetic field, a voltage is produced. The coil will rotate to cut through the south end, producing a voltage in the opposite direction. This means in every turn of the wire, positive and negative charges are produced: a.c. electricity.

Mind baffling? Here's a page with an animation, which might clear things up: http://www.wvic.com/how-gen-works.htm. It ain't over yet though...

Slip rings and brushes

Each end of the coil is attached to separate metal cylinders called slip rings. These make electrical contact with the coil and rotate with it.

To get the electricity to an external circuit, conducting brushes are used. These do not move, but they are in continuous contact with the rotating slip rings.

National Grid

Once our electricity is being generated, it needs to get to people's houses. It travels along the National Grid. It's power we're after from electricity, and the formula for it is P = V x I.

Therefore, you need either a lot of voltage or a lot of current. The only trouble with current is it produces a lot of heat because of resistance, which loses energy. So instead, a huge voltage is used.

Transformers "step up" the voltage to 40,000 and then it is carried along the wires to houses. Transformers at the other end "step down" the voltage, to safe levels.

All that trouble for a bit of electricity?

Go to top!


Energy Transfer

Now we've got the electricity, what do we do with it? Why did we go to all that trouble, and why does electricity blitz through most things around you? Simple answer: It's one of the easiest energies to convert to another form...

Here are some examples of ordinary house electricity conversions:
Application Energy Transfer
Radio/Speaker Electrical Energy -> Sound Energy
Light Bulb Electrical Energy -> Light Energy

 

Cooker

 

 Electrical Energy -> Heat Energy
 Fan  Electrical Energy -> Kinetic Energy
There are of course, other common energy transfers you ought to know:
 Milk float  Chemical Energy (battery) -> Kinetic Energy, Light Energy, Sound energy, etc.
 Rollar coaster  Kinetic Energy -> Gravitational potential.
 Bow  Elastic Potential Energy -> Kinetic Energy

Sadly, things aren't perfect. The reason? Some energy gets wasted in the conversion.

A typical lamp bulb, for example, will produce only 6 jewels of light for every 100 jewels provided. The rest is lost, mainly in heat.

Finding out how much useful energy is converted is called finding its efficiency. It's a fairly simple calculation:

If we use the previous light bulb example it's merely a case of dividing 6 by 100 = 0.06. Efficiency is always written as a percentage, so the efficiency of the light is 6%.

The more efficient something is, the better it is at converting the starting energy to the useful energy.

What about the wasted energy?

Most wasted energy ends up as either heat or sound, which will enter the environment. The energy will become more and more dissipated, meaning it is very difficult to do anything with it.

That's all there is to it!

Go to top!


Heat Energy The very last bit...

Heat can be transferred in three different ways: conduction, convection and radiation. All three are more "hot" than cool...

Conduction

This occurs in solids, though metals are the best conductors. The heat gives particles energy to only vibrate in a solid, which has a knock-on effect on their neighbors. Heat energy is passed this way.

Metals are much better conductors because they have free electrons. They move around and carry the heat energy from the hot part of the metal to the cooler regions.

Convection

Convection passes heat on through gases and liquid. Heating gives particles energy. In gases and liquids, this means the particles can move around everywhere. Hot air and water is less dense, as the particles are more spread out. The dense gas/liquid will sink while the hot rises.

Radiation

This requires no particles. The heat energy is emitted from the object as waves known as infrared.

  • Black, matt objects are better emitters and absorbers of heat.
  • Silver, shiny objects are better reflectors of heat.

This is why in hot temperatures, white t-shirts are worn - to reflect the heat. In good ol' Britain, of course, you get a lot of black clothing...

Keeping the home hot...

Because heat has a habit of escaping the house (you don't let the cold in, you let the heat out) it's important to prevent heat loss. There are several different methods, and some are better than others. Some are more expensive too...

Other methods include carpets to stop heat escape from the floors and curtains for the windows...

Cost effective or effective? You need to know the difference. The most effective is the one that naturally saves the most money, for example here it is Cavity Wall Insulation as that saves £70.

Cost effective though, is slightly difference. The cheaper ones are more cost-effective because you get your money back faster.

To find out which methods would be better in a certain scenario, you need to take into account how long you'll be staying in the house. Say you'll be living there for ten years:

Method
Initial Cost
Annual Saving
Saved over 10 years
Balance after 10 years
Double Glazing £2,000 £60 £600 £-1,400
Draught Proofing £50 £50 £500 £450
Cavity Wall Insulation £500 £70 £700 £200
Thermostatic Controls £100 £20 £200 £100
Loft Insulation £200 £50 £500 £300
Hot Water Tank £10 £15 £150 £140

As we can see from the table, it would be pointless to put in Double Glazing. For ten years, the best method would be Draught Proofing.

And that, my friends, is all you need to know for the Year 10 Physics! Happy revising!

Go to top! or Take a Quiz!


 

 

AQA homepage

BBC GCSE Bitesize

Pokemon Ultimate

Critique Circle

Level Up


All text copyright © 2006 to EJ Taylor. Page Template created by James Taylor. Site created: 10 April, 2006. Last revised: 2 August, 2015