Completed

The whole specification for IGCSE Physics has been completed (Yay!)
Good luck and happy studying.

7c) Particles

Geiger and Marsden's experiment with gold foil and alpha particles:
Experiment - Model with gold foil where nuclei of helium atoms (positively charged). If the model is correct all alpha particles would go straight through foil
Results - Some of the alpha particles bounced back meaning that inside the atoms there most be small positively charged nuclei which repels the passing alpha particles. So the model of the atom says that: most of the mass must be concentrated at the centre, nucleus must be small compared to atoms as very few alpha particles are deflected and negative charge (electrons) must be around the nuclear material.

Nuclear fission:
Is the splitting of a large nucleus (for example Uranium-235) into smaller fragments which is an artificial process so doesn't occur naturally- this releases energy.

Process steps:

1. The 'fuel' that is split in a nuclear reactor which is usually a stable isotope such as uranium-235 or platonium-239 
2. If a slow moving neutron gets absorbed by the nucleus the nucleus can split
3. Every time a U-235 nucleus splits up, it results in a small number of neutrons and chain reactions can occur if they go on to hit another U-235, causing it to split and release more smaller neutrons and so on. 
4. When a U-235 splits in two it will form two new daughter nuclei, usually Barium and Krypton- they are lighter elements than uranium
5. The new nuclei are usually radioactive
6. Each nucleus splitting gives out a lot of energy which is in the form of kinetic energy of the fission products - the daughter nuclei and (three) neutrons
7. This energy can then be converted into heat energy in the reactor by collisions with other atoms 

Nuclear Reactor:

1. free neutrons in the reactor start the fission process
2. The atoms produced the collide with other atoms causing the temperature to rise in the reactor
3. The moderator (water or graphite) slows neutrons so that they can successfully collide with uranium nuclei and chain reaction is controlled a steady output of heat
4. The control rods limit the rate of fission by absorbing excess neutrons- this also maintains a steady output of energy 
5. carbon dioxide or another gas is pumped through the reactor to carry away the heat generated 
6. The gas is passed through a heat exchanger and the water is heated turned to steam which turns the turbines and generator, generating electricity which can then be used by the National Grid to homes 

Nuclear waste? It's hard to find a suitable site to dispose and has to be stored until radioactivity levels are lower

(Extra: Nuclear Fusion is when two small nuclei are joined together, at the moment this can only occur naturally- an example of this would be the sun. This method doesn't produce waste and can be recycled)

7b) Radioactivity

Structure of Atoms:

The nucleus of an atom contains protons and neutrons. It makes up most of the mass of an atom, but virtually no space - tiny. in a nucleus are called the atomic number or proton number. The total
The electrons are negatively charged and are small. They are outside of the atom and take up the most space, giving it's overall size. 
The number of protons in a nucleus are called the atomic number or proton number. The total number of protons and neutrons in the nucleus are called the mass number or nucleon number.

Isotopes:
Have the same number of protons, but different number of neutrons (mass number/nuclear number)

Alpha Particles:

• made of 2 protons and 2 neutrons (like Helium) and are big, heavy and slow moving 
• don't penetrate far (easily stopped) 
• Strongly ionising 
• Electrically charged --> deflected by electric and magnetic fields
• emitting alpha particles decreases the atomic number by 2 and the mass number by 4 

Beta Particles

• Electron emitted from the nucleus of an atom when a neutron turns into a proton and an electron. When a beta particle is emitted the number of protons increases by 1, so the atomic number increases too
• Move quite fast and are small 
• penetrate moderately, and moderately ionising 
• Charged --> deflected by electric and magnetic fields 

Gamma rays

• no mass, just energy
• penetrate along way 
• weakly ionising 
• no charge and so isn't deflected 
• gamma emissions happen after alpha or beta decay --> no effect on atomic or mass number 

Penetrating power

Alpha --> blocked by paper, skin or a few cm of air 

Beta --> stopped by thin metal

Gamma --> thick lead or concrete 

Complete balanced nuclear equations:

Alpha decay

Beta decay

How to detect ionising radiation:

• radiation imprints on camera film 
• Geiger-Muller detector (GM counter) beeps in the presence, the more radiation the more frequency it beeps 

Where is it from?

Half Life:

• time taken for half of the radioactive atoms now present to decay 
•  

Uses and Dangers:
Alpha
detect a fire - ionises air, small current when smoke enters --> alarm goes off
Change cells - don't cause harm outside body, but most inside 

Beta
testing thickness - intensity proportional to paper thickness 
leaks in pipes - put in use GM counter
Change cell - can penetrate deeper into the body, not ionising 

Gamma
detect cracks - like an X ray 
Sterilisation - go through packaged source 
Medical imaging - inject radioactive tracer 
Radiotherapy - kill cancer cells 
Change cells - passed through flesh, bones absorb gamma rays (most) and not very ionising 

7a) Units

• Becquerel (Bq) 
• Centimetre (cm) 
• Hour (h) 
• Minute (m) 
• Second (s) 

Section 7

Radioactivity and Particles

6d) Electromagnetic Induction

Electromagnetic Induction: The creation of a voltage (and maybe a current) in a wire which is experiencing a change in magnetic field.

To get a bigger voltage....
Increase the strength of the magnet
Increase the speed of movement
Increase the number of turns on the coil

You can reverse the current direction:
reverse the magnetic field by flipping the magnet
switching/ change the direction of wire movement

Only get an induced current if it is part of a complete circuit, otherwise it would be an induced voltage (will always be an induced voltage)

Factors that increase the amount of electricity being produced: strength of magnetic field, number of coils in wire, speed of rotations

Paper Two- Transformers 

Is a device which can increase or decrease the value of an alternating voltage by having different number of turns on input and output sides. It consists of two coils wound round an soft iron core. 

    

Step-Up Transformers

• increases the voltage by more turns on the secondary coil than primary

Step-Down Transformers

• decreases the voltage by having more turns on the primary coil than secondary

input(primary)voltage/ output(secondary)voltage =  primary turns/ secondary turns 

Vp/Vs = Np/ Ns 

Transformer efficiency:

= Power output from secondary coil / Power input to primary coil 

= (I_sV_s) / (I_pV_p) x 100% 

(I_sV_s) / (I_pV_p)

 when a transformer is supplying current, it is almost 100% efficient 

6c) Electromagnetism

Magnetic fields in current-carrying wire:

• an electric current in a material produces a magnetic field around it 
• the larger the electric current, the stronger the magnetic field 
• the direction of the magnetic field depends on the direction of the current 

Paper Two-

Straight wire, Flat circular coil and Solenoid:

The magnetic field around a straight wire is circular:

The magnetic field around a flat circular coil ellipses (egg-shaped):

The magnetic field around a solenoid  is electromagnet: 

If something with a charge is moving across a magnetic field it will 

experience a force from the field, unless it's parallel. 

D.C. Electric Motor (simple):

• wire in magnetic field 
• force turns a 'split ring communicator' ---> charge goes from brushes in wires 

      Four factors

1. more current 
2. more turns on coil 
3. stronger magnetic field 
4. soft iron core 

Loudspeaker:

• force pushes current away from field, pushes core which makes sound ---> cone vibrates 

The left hand rule:

Helps to figure out the thrust/motion, field and current of the wire to then work out which way the force is acting.

Wire in magnetic field increase (<) current = more force on wire 

Wire in magnetic field increase (<) strength = more force on wire 

6b) Magnetism

 Paper Two- 
Repel and attract

Opposite poles attract to one another:


Same poles repel one another:


Magnetic substances can also be attracted by a magnet

Properties of a magnetic material

Magnetically hard material ---> retains its magnet properties for a long period of time/permanent. hard to demagnetise

Magnetically soft material ---> loses its magnetic properties almost as soon as the magnet field leaves

Magnetic field lines:

• represent shape and direction of magnetic field 
• gives an idea of magnetic field 

Induced Magnetism;

When a magnet is brought near a magnetic material then the material will acts as a magnet because the magnetic field encourages them to align and form poles. Examples: iron, cobalt and nickel. 

The closer the magnet, the stronger the induced magnetism becomes. 

Experiments to find the magnetic field pattern of a permanent magnet and two bar magnets:
Can use multiple compasses or iron fillings to see the magnetic field.

     

Hold two opposite poles close together so that they attract
and makes a uniform magnetic field:

6a) units

• Ampere (A) 
• volt (v) 
• watt (W) 

Section 6

Magnetism and electromagnetism

5d) Ideal gas molecules

Particle theory says that gases consist of very small particles which are constantly moving in completely random directions.

Brownian motion supports the particle theory because large, heavy particles can be moved with Brownian motion with smaller, lighter particles travelling at a high speed. This is way particles appear to be moving around randomly when you observe them in a lab.

Gases have a random motion, so when they collide with something they exert a force on it, and their momentum and direction change.
In a sealed container gas particles smash particles against the container walls- this creates an outward pressure. The pressure depends on how fast the particles are going and how often they hit the walls (average speed)

Absolute Zero
The coldest that anything can get is -273℃ - this temperature is called/ known as the absolute zero. At the absolute zero, atoms have little kinetic energy as it's possible to get.

Kelvin scale
unit: K
begins at the absolute zero (-273℃) and so there are no minus numbers

temperature in degrees Celsius = temperature in Kelvin - 273
temperature in Kelvin = temperature in degrees Celsius + 273

The temperature of a gas (in Kelvin) is proportional to the average kinetic energy of its particles

As the kelvin increases, energy increases. As the energy of something increases, its particles will move faster and with more force. This means that more force is exerted over a fixed area increasing the pressure.
So if a gas has its kelvin increased, it will exert more force on its container, and then pressure goes up.

pressure/ temperature (in K) = constant 
p/T = constant 
or: p₁/T₁ = p₂/T₂

pressure x volume = constant 
pV = constant 
p₁V₁ = p₂V₂ 

5c) Change of State

Whole Part is for Paper Two ONLY

SOLID	LIQUID	GAS
regular pattern	irregular pattern	widely spread
close together	random arrangement	random arrangement
vibrate	move around each other	move quickly around in all directions
can't be compressed	can't be compressed	can be squashed or compressed