# P3 (Edexcel)

(Information is from CGP revision book - I do know own the information, it is how I revise)

Triple Physics.
Topics:
Particles in Action:

• Kinetic theory and temperature in gases
• Kinetic theory and pressure in gases
• particles in an atom
• fundamental particles
• electro beams

Medical Physics:

• Total internal reflection
• medical uses of ligh
• energy metabolic rate
• intensity of radiation
• nuclear bombardment
• momentum conservation
• medical use of radiation
• medical research

The ___________ Divide line does not appear on some cards - do put it in yourself!  :)

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• Created by: Ga
• Created on: 14-04-12 16:29

## Kinetic Theory and Temperature of gases

Kinetic theory says Gases are: Randomly moving particles, in random direction. Also, the constantly collide and bounce of one another.

Absoloute zero : Is the coldest measurement at 0k or -273 'C

If you increase the temperature of something you give the particles more energy and they move more quickly.  Absolute Zero is when the atoms have as little kinetic energy as its possible to get.

To convert degrees Celsius to Kelvin, just ADD 273. And to convert Kelvin into degree Celsius, just SUBTRACT 273.
-Kinetic Energy is proportional to Temperature... Increase the temperature, increase the kinetic energy

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## Kinetic theory and Pressure in gases

Kinetic theory say: Colliding gas particles create PRESSURE.
When they collide with something, they exert a force a force on it. In a sealed container smash against the container's walls - creating an outward pressure.

- This pressure depends on how fast the particles are going, and how often.
If you heat the gas, the particles move faster and have more kinetic energy. Meaning that the particles will collide more often, creating more pressure. Temperature and pressure are directly proportional.
As the pressure doubles, the volume halfs (needs a fixed temp)
And if you put the same amount of gas in a bigger container , the pressure will decrease. (Inversely proportional)
EQUATION: Pressure   = Constant /OR  P1V1 =  P2V2                                          Temperature                          T1          T2

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## Particles in Atoms (Alpha)

Known properties of Alpha , Beta  and Gamma radiation .

Alpha is a helium nucleus 4/2He, and it is slow and heavy. It is strongly ionising however, it is stopped by paper and or skin. It is emitted when there are 82 protons because it is unstable due to having a heavy nuclei. There is a change as a result of the decay, within the nucleus 2 protons and 2 neutrons leave the nucleus and the mass number is down by 4. The proton number is also down by 2
For example:

Uranium(238/92) -> Th(234/90) + He(4/2)

The uranium has too heavy nuclei making it unstable. So when the alpha (Helium) is emitted, the end product Th has a reduced mass of 4, and proton number of 2.

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## Particles in Atoms ( Beta Negative)

Beta is an electron 0/-1e , it is light and fast. It is moderately ionising and it stopped by aluminium (thin metal).
Beta Negative or Beta  , is emitted when it has too many neutrons (when it is "neutron Rich") making it unstable. It can not get rid of the neutron because it is stuck together firmly instead, It converts the neutron into a proton whilst emitting an electron giving it the negative charge.

The electron is the radioactive decay. So the change in the nucleus is that a neutron is converted into a proton, and there is no change in the mass number. Although the proton number is increased by one. For example:187/75 Re -> 187/76Os + 0/-1e.

The Re emits an electron and makes the end product Os have the same mass number and an extra proton.

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## Particles in Atoms (Beta Positive)

Beta positive + is an anti-matter of beta negative. This basically means that it has the same properties as B- but it has an opposite charge.

Beta positive happens when it has too few neutrons which makes it unstable. To make it stable the proton changes to a neutron whilst emitting an electron but it has a positive charge. The mass number does not change but the proton number is decreased by one.

For example:
37/20 Ca -> 37/19 K + 0/+1 e

Because Beta + decay happened, the potassium proton number is decreased by one and the mass number stays the same.

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## Particles in atoms (Gamma)

Gamma radiation ()is an Electromagnetic radiation, it doesn't have any mass which means it is very fast. It is weekly ionising and its stopped by thick lead or thick concrete.

It occurs when the nuclei has too much energy after Alpha  or beta radiation. Its was of loosing energy is emitting Gamma radiation.

You never get gamma rays  emitted, it always goes with beta or alpha

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## N-Z graph

Any isotope which does not lie on the curve is unstable.

An isotope that lies above the curve has too many neutrons to be stable.

An isotope that lies below the curve has too few neutrons to be stable.

And an isotope that has more than 82 neutrons is unstable.

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## Fundamental Particles

Electrons and Positrons are FUNDAMENTAL PARTICLES. This means that they cannot divide into smaller particles.

Scientists can make NEW fundamental particles because when two protons collide at very high speed they release energy and this energy can turn into mass. This mass makes equal amounts of matter and anti-matter.

HOWEVER, Protons and Neutrons are not fundamental particles, they are made up by smaller particles called quarks. Three quarks makes up either a proton or a neutron.

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## Quarks [Fundamental particle]

Quark     Relative charge       Relative Mass
Up              2/3                        1/3

Down          -1/3                        1/3

- Proton =  2/3 + 2/3 + (-1/3) = +1        (Up, Up + Down)
- Neutron =  2/3 + (-1/3) + (-1/3) = 0    (Up, Down + Down)

A proton has a mass of 1 and a positive charge. A neutron has no mass and no charge.

When a proton is converted into a neutron, or visa versa. One of the quark changes. So when a neutron turns into a proton the nucleus has to produce a negative charge to keep the overall charge as 0. A proton into a neutron (up into a down)a positive charge is needed to keep it as an overall + charge.

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## Electron Beam

An Electron Gun uses THERMIONIC EMISSIONS.

What happens:
-The heater heats the CATHODE which gives more energy to the electrons. Once they have enough energy they are delocalised from the atom i.e they escape. This process is called Thermionic Emissions
- The electrons then accelerate, being pulled towards the ANODE.
-The Anode has a gap in it to channel the electrons into an electron beam.
-An ELECTRIC FIELD created between charge metal plates are used to deflect the electrons.
-The Phosphorescent Screen glows when the electrons hit it.
-Electron gun is vacuum tubes are also called CATHODE RAY TUBES.

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## Electron Beam

You can calculate the Kinetic Energy of each Electron.

The electron charge is -1.6 x 10^-19

EQUATION:
Kinetic energy = Charge of the electron x accelerating voltage.

You can also calculate the current produced.

EQUATION:
Current = charge (n x e)/time

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## Electron Beam

An Electron beam is DEFLECTED by an electric field.
An electron beam is attracted by a positive charge, and repelled by a negative charge.Using two pairs of charged metal plates, the electron beam can be deflected both up and down (by the Y-plates) and left and right (by the X-plates). Any stream of charged particles can be deflected like this, eg. a jet of charged ink particles.
How much particles are deflected by depends on four factors:
More deflection:

• Bigger Charge on plate
• Bigger Charge on particles
• Slower and lighter moving particles

Less deflection:

• Smaller charge on plates and particles
• Faster and heavier particles
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## Electron Gun (Ocsilloscope)

They are used in Tvs, Oscilloscopes, and to make X-rays.

Oscilloscopes:
An Oscilloscope is a device for displaying voltage and frequency of an electric signal. On a oscilloscope screen the X axis represents the time and the Y axis represents voltage
The voltage applied to the X plate in the electron beam controls the time base or how quickly the electron moves across the screen, The voltage applied to the Y plate affects the pattern displayed on the screen.
The voltage amplification control, adjusts the size of the display - the greater the y voltage the higher the amplitude of the image.

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