physics revision guide

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  • Created on: 29-05-12 09:38
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Particles in action
Radioactivity
Alpha ()
Strong ionising
Only travels a few centimetres in air
Stopped by a thin sheet of paper
Helium mass
Alpha decay
The breakdown of a large mass
Occurs with isotope that have 82+ protons
Beta ()
Is ionising
Stopped by 3mm of aluminium
Beta + decay
The process of a proton changing into a neutron
Products: neutron and positron
Beta - decay
the process of a neutron turning into a proton
products: a proton and electron
Gamma ()
energy ,ray and way
gamma decay
weak ionising
a by-product of a or decay
Interactions of radiation with matter
Alpha particle ­ the e- is pulled by the positive alpha particle
Beta-particle ­ the electron is pulled out by the beta- particle
Gamma ­ the electron gains energy from gamma
Neutrons ­ neutrons can't react but may release a gamma ray if it hits the nucleus.
Positron
e+ -
positive e+
meets an
electron
creating

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­ in the photon effect a photon interacts either with an electron which is bound
in an individual atom or with an electron in condensed matter, usually solid, which is not bound
*
Crompton effect ­ in Crompton effect, the photon
scatters from a free electron or a loosely bound atomic electron. The scattered photon has less
energy than the incident photon and excess energy is transferred to the electron.…read more

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Electron gun
1. The source of electron is a metal (cathode)
2. A low voltage supply heats the filament giving the electron
enough energy to leave the surface
3. A high voltage from a d.c. power supply is connected
between the cathode and anode pulling the electron towards the
anode
4. The shape of the anode focuses the electron into a beam.
They are accelerated by the attractive force.
5. The speed of the electrons depends on the voltage of the
high voltage supply.…read more

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Gas properties and pressure
Pressure and volume
The exerted force by the particles hitting the container surface gives the gas pressure. The smaller
the volume the more collisions there would be, so the gas pressure increases.
Pressure and temperature
As the temperature increases the pressure increases in a constant volume.…read more

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Conservation of momentum:
The momentum before collision is the same after.
Energy, work and power
GP E (J ) = m (kg)×g ( kg ) ×N
h (m)
power (W ) = work done or energy transferred (J )
time (s)
Energy and intensity
W
( m2) intensity= power
area
Voltage
V T = V 1 + V 2 + V 3
Adding the measurements on the three voltmeters gives the
power supply potential difference (p.…read more

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Pulse oximetry
The pulse oximeter is for measuring the oxygen in the blood in the arteries. A sensor (a photodiode)
is placed on one side of the finger to detect a beam of red light, from an LED and a beam of infrared
radiation from an IRED. The ratio of the red light to the infrared radiation absorbed on passing
through the finger gives a measure of the percentage of oxygen in the blood.…read more

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PET scan
The tracers depend on what the scan is for. A commonly used radioisotope is fluorine-18. A nucleus
of F-18 is used to replace an oxygen nucleus in a sugar molecule. When the radioactively tagged
glucose is injected into the bloodstream, it travels to parts of the body that use glucose for energy.
Malignant tumours show up because they use glucose differently to normal cells. The nucleus decays
to an oxygen-18 nucleus, so the glucose does not change into a different compound.
1.…read more

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