2b) Electricity and The Atom Flashcards
What is the UK mains supply (approximately)?
230v
Alternating Current supply (AC)
What is an electric current?
Movement if charge carriers
What is the frequency if the AC mains supply?
50 cycles per second
50 Hz
What is AC and DC?
Alternating Current - mains supply
Current is constantly changing direction
Direct Current - cells/batteries
Current flows in the same direction
How can you work out the frequency of a supply?
Frequency = 1/time period
What is a time period on an oscilloscope?
Time taken to complete one cycle
What do the gain dial and time base dial control on an oscilloscope?
Gain dial - how many volts each centimetre division represents on the vertical axis
Time base dial - how many milliseconds each division represents on the horizontal axis
How much is one millisecond in seconds?
1ms = 0.001s
What are the metal parts of a plug made out if and why?
Copper or brass
Very good conductors
What is the case, cable grip and cable insulation made out of and why?
Rubber or plastic
Good insulators and flexible
What 3 coloured wires do most cables have?
Brown live wire - alternates current from positive and negative voltage
Blue neutral wire - 0v
Earth wire - carries electricity to Earth for safety and to prevent fires and shocks
What does earthing mean?
Case must be attached to an earth wire which can never become live
All appliances with metal cases are earthed to reduce risk of electric shock
When is an appliance double insulated?
If the appliance has a plastic casing and no metal parts showing
Doesn’t need an earth wire
Only live and neutral (two-core cables)
What is a circuit breaker?
An electrical safety device which protect the circuit from damage if too much current flows
What does an RCCB stand for?
Residual Current Circuit Breaker
Why are circuit breakers better than fuses?
Easily reset by flicking a switch
More convenient than fuses which gave to be replaced
Even work for small current changes which aren’t big enough to melt a fuse
Quicker - safer
What is an isotope?
Different forms of the same element
Atoms with the same number of protons but a different number of neutrons
What does it mean by an isotope is radioactive?
It decays into other elements and gives out radiation
What is background radiation?
Radiation that is present at all times, all around us
Where does the background radiation we receive come from?
Naturally occurring isotopes around us - in the air, in fold, in rocks etc.
From cosmic rays mostly from the sun in space
Due to man-made sources - nuclear accidents like Chernobyl or dumped waste
What are the three types of radiation?
Alpha
Beta
Gamma
Describe an alpha particle
Two neutrons and two protons Same as helium nucleus Relatively big, heavy, slow moving Don't penetrate very far into materials and are stopped quickly Strongly ionising
What does the term ionising mean?
When atoms bash into other atoms and knock electrons off them
Describe beta particles
They are Electrons Move quite fast and are small Penetrate moderately into materials Moderately ionising Long range in air Virtually no mass Charge of -1
What happens in the nucleus when a b-particle is emitted?
For every b-particle emitted, a neutron turns into a proton in the nucleus
Describe gamma rays
Opposite of alpha particles
Penetrate far into materials without being stopped
Pass straight through air
Weakly ionising - tend to pass through atoms rather than collide
No mass and no charge
Very short wavelength EM waves
What happens when a nucleus decays by alpha emission?
It’s atomic number decreases by two (two less protons)
It’s mass number decreases by four (two less electrons as well as protons)
What happens when a nucleus decays by alpha emission?
Increases the atomic number by one (one more proton)
Mass number doesn’t change (same electrons and same neutrons)
What is a half-life?
The average time it takes for the number of nuclei in a radioactive isotope to halve
How can nuclear industry workers ensure they aren’t being exposed to too much radiation?
Wearing protective clothing and face masks to stop them touching or inhaling radioactive material
Monitor their radiation doses through regular check-ups
How can radiographers ensure they aren’t being exposed to too much radiation?
Wearing lead aprons
Stand behind lead screen to protect them from prolonged exposure to radiation
What does radiation dose or the amount of radiation your exposed to depend on?
Location - underground rocks release radioactive radon gas, high altitudes have more exposure to cosmic rays
Occupation - nuclear industry workers, radiographer, miners and pilots have higher risks
Describe the charges on each type of radiation
Alpha: positive charge
Beta: negative charge
Gamma: no charge (neutral)
What happens to each type of radiation when travelling through a magnetic or electric field?
Both alpha and beta particles deflected but in opposite ways
Alpha particles deflected less because they have a larger mass
Gamma has no charge so it doesn’t get deflected
What is the unit for measuring radioactivity?
Becquerel (Bq)
1 Bq means one nucleus decaying per second
What happens to the radioactivity of a sample over time?
It decreases
What is the count rate?
Number of radioactive emissions detected per unit of time
What is nuclear fission?
Splitting up of big atomic nuclei
What is nuclear fusion?
Joining up of small atomic nuclei
Happens in the sun
State some uses of radiation
Smoke detectors - alpha
Tracers on medicine - short life beta or gamma
Radiotherapy - treatment of cancer - gamma
Sterilisation - gamma
Life cycle of a star bigger than the sun
Protostar Main sequence star Red super giant Supernova Neutron star Black hole
Life cycle of a star same size as the sun
Protostar Main sequence star Red giant White dwarf Black dwarf
