Matter that is made out of quarks

Exam questions will basically deal with up, down and strange quarks.

Remember that in any interaction, the baryon number on the left must be same as the baryon number on the right. Strangeness does not have to be conserved.

Four fundamental forces

All forces in physics can be reduced to these four:

In line with quantum theory, which says that everything has to come in lumps, the forces work by the exchange of particles (lumps).

The particles are called gauge bosons and they are called virtual particles because they only exist as messengers between two particles carrying the force. They can never exist on their own because they would be meaningless.

To imagine repulsion caused by exchanging particles, think of two skaters approaching each other on ice.

· A throws a heavy ball to B.
· Conservation of momentum means that A is pushed away from B.
· B catches the ball from A.
· Conservation of momentum means that B is pushed away from A.

Feynman diagrams

This is for people who are re-sitting module 1.

Remember that a Feynman diagram shows the way that particles interact:




This example shows two protons repelling each other. Remember that a photon of an electromagnetic wave is the particle that carries the force for electromagnetic forces.








We start to read this example in the bottom left hand corner. A single neutro appears. Then something happens that produces a proton and two other particles. The neutron must have decayed.

The other two particles are created from a W-. This is the particle responsible for the weak nuclear force.

This example is called beta decay, because the electron produced is ejected from the nucleus.



This is another version of the same beta decay. This time it shows the quarks that make up the neutron at the start. It allows us to see that beta decay causes one of the quarks to change flavour.

The Pressure Law

This is for the case when you have

• Fixed mass of gas
  Constant Volume

When we did the experiment in class, this is what we got:

We extended the line backwards to the point at which there was zero pressure. If the pressure is zero then the molecules are no longer moving and are thus unable to crash into the walls of the container. Each molecule has zero kinetic energy. Using the rule:

Average kinetic energy of one molecule = 3/2 kT

Zero kinetic energy will mean zero temperature. So we call this point (-273oC) ABSOLUTE ZERO.

Finally we can re-plot the graph with a temperature scale in Kelvin starting from Absolute Zero.

Now we have a proportional pattern and we can conclude that:

• Pressure is proportional to absolute temperature
• Double the Kelvin temperature, double the pressure
• p/T = a constant
• p1/T1 = p2/T2

Charles' Law

This is for the case when you have

• Fixed mass of gas
• Constant pressure

When we did the experiment in class, this is what we got:

The above graph looks strange because we could only do a range of temperatures from ice to steam.

Next we extended the line backwards until we had zero volume. You can't have less than zero volume so it must have the lowest possible temperature, ABSOLUTE ZERO.

Finally, we have the case where a new temperature scale is invented starting at ABSOLUTE ZERO. This graph passes through the origin (because we moved the origin!) so we get a proportional pattern

It means

• Volume is proportional to absolute (Kelvin) temperature
• Double the Kelvin temperature, double the volume
• V/T = a constant
• V1/T1 = V2/T2

It is explained by saying that molecules are moving faster at a higher temperature so they spread further apart.

Be prepared to draw extra lines on the graph through absolute zero for

• Higher constant pressure
• Lower constant pressure

Boyle's Law

Remember that for an ideal gas there are 4 large scale measurable properties:

• Total mass of the gas
• Pressure of the gas
• Temperature of the gas
• Volume of the gas

Boyle's Law is the rule for a fixed mass of gas at constant temperature.

Here is the graph to show how volume varies with pressure:

It's not rocket science. High pressure means that you are squeezing the the gas so the volume must go down.

The mathematical pattern is:

• Volume is inversely proportional to pressure
• pV = a constant
• p1V1 = p2V2
• Double the pressure, halve the volume

You need to know how to draw further curves on the graph

• Above the existing curve for higher temperature - the particles will be moving faster pushing outwards into a bigger volume and causing more pressure
• Below the existing curve for lower temperature

Electric power question

The question that you were set was about a hairdryer with two heating wire coils in parallel. The first part about calculating the length of the wire went well. It was 3 metres. You then calculated the power of R1 which was 300 Watts (to 1 sig fig)

In the second part, it said that wire 2 was then connected in parallel and there was 3 x the power used.

This is the easy way to solve it.

Three times the power means a combined output of 900 Watts. But R1 is already giving out 300 Watts so R2 must give out 600 Watts.

R2 on its own has twice the power of R1, but the supply voltage is the same.

P=IV

So twice the power means twice the current.

If twice as much current is getting through, then wire 2 must have half the resistance.

Half the resistance means half the length.

Wire 2 is 1.5 metres.

Specific heat capacity

Specific heat capacity is the amount of energy needed to make the temperature of 1 kg of water go up by 1 Kelvin.

Note that the size of 1 Kelvin is actually the same as 1 Celsius. Temperature changes are the same whether they are measured in Celsius or kelvin.

So in specific heat capacity questions you don't need to change the temperatures into Kelvin.

The formula is on the data sheet.

They will either give you the specific heat capacity in the question or give you enough data to calculate it.

Past papers

You can get copies of past papers and mark schemes from the AQA website. We are studying Physics Syllabus A.

http://www.aqa.org.uk/qual/gceasa/phyA_assess.html

If you want to see the syllabus, you can click on "Specifications" at the top of the page. The 2007 syllabus is available as an Adobe file. You were given a hard copy of the syllabus, but it may be that your filing is terrible.

You want the bits called Subject Content
AS Module 2
AS Module 3

(and AS module 1 if you are re-sitting the January exam)

The syllabus is a useful list of things you need to revise.

Resultant force

When they use the words "resultant force" in an exam question, they want you to talk about the balance between the driving force and the counter force on an object. They then want you to link it with the equation for Newton's Second Law:

Resultant force = mass x acceleration

F = ma

A favourite example is an object falling through air.

• At first, the only force is gravity(weight) downwards. It is not yet going fast enough for there to be air resistance. Gravity is the winner and hence the resultant force is downwards. There is a resultant force so the object accelerates, going faster.
• A faster object has more air resistance.
• The weight of the object does not change. So the force downwards stays the same whilst the the counter force upwards keeps increasing.
• The resultant force gets smaller and smaller. The objects keeps accelerating but the speed goes up by less and less each time.
• Eventually air resistance upwards = weight downwards.
• There is ZERO resultant force.
• There is NO acceleration.
• The object stays at the same speed, TERMINAL VELOCITY.