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.
The exam board love those "three formula" and this is an example of one:
= Voltage ÷ Current or
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...
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...
Resistance and gradient: The steeper the graph line, the lower the resistance. Pretty obvious if you think about it.
And that's the first horrible bit of electricity done! :)
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...
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:
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:
Which are which? C'mon, this is all really basic stuff!
Advantages and Disadvantages
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.
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?
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:
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!
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...
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 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.
This requires no particles. The heat energy is emitted from the object as waves known as infrared.
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:
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!