GENERATING ELECTRICITY

radioactive decay, fusion and fission all give off…

energy

what is radioactive decay

completely spontaneous, has one daughter nuclei product and alpha/beta particle

what is fission

fission is non-spontaneous

* requires a neutron fires at nucleus

it has two daughter nuclei and 3 neutrons as products

what is fusion

fusion happens in stars

it joins two nuclei together to make one nucleus

describe the process of fission in a Uranium 235 nucleus

* a neutron is fired at the nucleus
* the U235 nucleus splits into two daughter nuclei
* a small number of individual high energy neutrons are also given off
* energy is released

what can be caused by the neutrons given off by fission

the high energy neutrons can then target more U235 nuclei causing more fission

* CHAIN REACTION

write the chemical reaction of the fission of U235

235/95U + 1/0n -→ 140/55Cs + 93/37Rb +3(1/0n)

function of fuel rods in a nuclear reactor

source of the U235

function of shielding in a nuclear reactor

prevents any radioactive material escaping by absorbing the radioactive decay

function of control rods in a nuclear reactor

control the rate of reaction.

* rate of reaction is too high, the rods are lowered
* they absorb excess neutrons and reduce the rate of fission
* if the rate of reaction is too slow, the rods are lifted
* allows the rate to increase

function of the moderator in a nuclear reactor

absorbs some of the energy of the high energy product neutron, slowing them down to a more moderate speed so fission can still take place but at a more controlled rate

describe the process of fusion

* smaller nuclei combine into a larger nuclei
* occurs in stars
* creation of a larger nucleus results in a loss in mass from the smaller nuclei and a release of energy
* requires high energy, pressure and temperature in order to overcome the electrostatic repulsion between protons

the nuclei in fusion are always…

positively charged

* repel eachother
* need high kinetic energy to overcome

waste products of fusion are…

still radioactive

waste products of fusion can cause…

cancer/mutations in humans

where is the waste product of fusion typically stored

in mountains/underground

what protects humans from the products of nuclear fission in a reactor

concrete around the core of the reactor

waste products of fusion can cause…

cancer in humans

what happens if the rate of reaction gets too high in a nuclear reactor

it explodes

what is the function of the live wire in a plug?

carries charge

what is the function of the earth wire in a plug?

grounds the plug

what is the function of the neutral wire in a plug?

completes the circuit back to its source

what is a fuse

a small piece of wire that melts and breaks the circuit if a surge occurs

what are 3 hazards of mains electricity

1. damaged insulation
* touching exposed wire -→ electrocution
2. overheating cables
* caused by too much current in the wire
* leads to a fire of melting of insulation
3. damp conditions
* water + wires -→ water conducts electricity
* short circuit = fire
* electrocution

explain differences in current and voltage in mains vs cell

cell: produces direct current, voltage is much lower than mains

mains: produces an alternating current (50hz), voltage is much higher (230V)

describe the generator effect

* movement of a magnet through a coil
* magnetic feild ‘cuts’ the coil
* induces a voltage
* a complete circuit means there is a current

how to increase voltage produced by the generator effect

* increase number of coils
* increase stregth of magnet
* move it faster

describe how a transformer works

1. the a.c supply provides an alternating current to the primary coil
2. the ac creates a changing magnetic feild around the primary coil
3. the soft iron core strengthens and channels the changing magnetic feild over to the secondary coil
4. the changing magnetic feild is being cut by the secondary coil
5. this induces a alternating/changing voltage and a current if circuit is complete

transformers only work with ac or dc?

ac as they depend on a changing magnetic feild

does the iron core conduct current in a transformer?

no it channels the changing mag feild

what is a step up transformer

it increases voltage in secondary coil in comparison with the primary coil (more turns in secondary coil)

what is a step down transformer

it decreases voltage in secondary coil in comparison with the primary coil (less turns in secondary coil)

what is the equation that links no of coil turns with voltage

voltage (primary)/voltage (secondary) = no of turns in coil (primary)/no of turns in coil(secondary)

how efficient are transformers

100%

what is the equation that shows the efficiency of the transformer is 100%

current (primary) x voltage (primary) = current (secondary) x voltage (secondary)

how do transformers work in power transmission lines

* the step up transformer drastically increases the voltage
* high voltage, low current
* current causes heating effects in wires, so a smaller current wastes less energy from heat loss
* the cables are very thick in order to decrease their resistance, reduces power loss
* the step down transformer at the end reduces the voltage to an appropriate amount for household use (240V)

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how renewable is solar energy?

renewable

cost

efficiency

conditions

does it work all the time

light energy -→ electrical energy

* renewable (no pollution)
* no fuel cost
* expensive to buy
* can provide energy in areas with no mains
* inefficient
* does not work at night or when its cloudy

how renewable is wind energy?

renewable

cost

efficiency

conditions

does it work all the time

kinetic energy -→ electrical energy

* renewable
* no fuel cost
* weather dependant (needs high wind speed)
* noisy and ruins views

how renewable is tidal energy?

renewable

cost

efficiency

conditions

does it work all the time

kinetic energy -→ electrical energy

* renewable
* no fuel cost
* reliable
* expensive to build
* destroys habitats
* easy to switch on

how renewable is biomass energy?

renewable

cost

efficiency

conditions

does it work all the time

chemical -→ electrical

* if replaced - sustainable
* cheap
* readily available
* no increased CO2 levels overall (biomass takes up co2 when growing)
* gives off atmospheric pollutants when burned

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how renewable is geothermal energy?

renewable

cost

efficiency

conditions

does it work all the time

thermal -→ electrical

* renewable
* no fuel cost
* hot water + steam can heat houses directly
* only available in certain volcanic areas

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how renewable is hydroelectric energy?

renewable

cost

efficiency

conditions

does it work all the time

gravitational potential -→ kinetic energy -→ electrical

* renewable
* no fuel cost
* easy to switch on
* reliable
* expensive to build
* floods farmland/forces poeple out of homes

how renewable is nuclear energy?

renewable

cost

efficiency

conditions

does it work all the time

nuclear -→ electrical

* no pollutants
* reliable
* non renewable
* accidents lead to radioactive material in atmosphere