2b) Electricity and The Atom Flashcards by Aish Sehgal

What is the UK mains supply (approximately)?

230v

Alternating Current supply (AC)

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What is an electric current?

Movement if charge carriers

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What is the frequency if the AC mains supply?

50 cycles per second

50 Hz

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What is AC and DC?

Alternating Current - mains supply
Current is constantly changing direction

Direct Current - cells/batteries
Current flows in the same direction

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How can you work out the frequency of a supply?

Frequency = 1/time period

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What is a time period on an oscilloscope?

Time taken to complete one cycle

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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

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How much is one millisecond in seconds?

1ms = 0.001s

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What are the metal parts of a plug made out if and why?

Copper or brass

Very good conductors

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What is the case, cable grip and cable insulation made out of and why?

Rubber or plastic

Good insulators and flexible

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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

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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

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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)

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What is a circuit breaker?

An electrical safety device which protect the circuit from damage if too much current flows

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What does an RCCB stand for?

Residual Current Circuit Breaker

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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

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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 ```