2011 EdExcel Unit 1. This PowerPoint supports Topic 5 (Generating and transmitting electricity) from the 2011 EdExcel Physics Unit 1 module. W Richards. Topic 5 – Generation and Transmission of Electricity. Electric Current.
This PowerPoint supports Topic 5 (Generating and transmitting electricity) from the 2011 EdExcel Physics Unit 1 module
Note that electrons go from negative to positive and are “pushed” by the voltage
Electric current is a flow of charge around a circuit
By definition, current is “the rate of flow of charge”
Electric current is when electrons start to flow around a circuit. We use an _________ to measure it and it is measured in ____.
Potential difference (also called _______) is how big the push on the electrons is. We use a ________ to measure it and it is measured in ______, a unit named after Volta.
Resistance is anything that resists an electric current. It is measured in _____.
Words: volts, amps, ohms, voltage, ammeter, voltmeter
If a battery is added the current will ________ because there is a greater _____ on the electrons
If a bulb is added the current will _______ because there is greater ________ in the circuit
Power is defined as “the rate of transferring energy” and is measured in units called “Watts” (W).
The amount of power being transferred in an electrical device is given by:
Power = voltage x current
in W in V in A
Coal, oil and gas are called “fossil fuels”. In other words, they were made from fossils.
A “fuel” is something that can be burned to release heat and light energy. The main examples are:
A renewable energy source is clearly one that can be _______ (“renew = make again”), e.g. _____, solar power etc.
A ___________ energy source is one that when it has been used it is gone forever. The main examples are ____, oil and gas (which are called ______ ____, as they are made from fossils), and nuclear fuel, which is non-renewable but NOT a fossil fuel.
Words – non-renewable, coal, fossil fuels, wood, renewed
1) A fossil fuel is burned in the boiler
2) Water turns to steam and the steam drives a turbine
3) The turbine turns a generator
4) The output of the generator is connected to a transformer
5) The steam is cooled down in a cooling tower and reused
When a fuel is burned the two main waste products are _____ dioxide and ________ dioxide.
Carbon dioxide is a _________ ___ and helps cause _______ _________. This is produced when any fossil fuels are burned.
Sulphur dioxide, when dissolved in ________, causes ______ _____. This is mainly a problem for ___ power stations.
Nuclear power stations do not produce these pollutants because they don’t ____ fossil fuels.
Words – sulphur, coal, global warming, carbon, acid rain, greenhouse gas, rainwater, burn
The main difference is that the nuclear fuel is NOT burnt – it is used to boil water in a “heat exchanger”
These work in a similar way to normal power stations:
Different power stations have different start up times:
Coal, oil, gas and nuclear
Pollution – CO2 leads to global warming and SO2 leads to acid rain
Cheap fuel costs
Generate a lot of energy
Fuel will run out
Easy to use
Wind, tidal, solar etc
Often depend on the weather – is it sunny???
Won’t run out
Energy is “dilute” – in other words, it’s very spread out
Can we drive the turbine directly without burning any fossil fuels?
Biomass can be used as a fuel in a number of ways:
Biofuels have two main advantages over traditional fuels – they are ______ and ________. However, they still release ______ _______.
Words – alcohols, cleaner, burnt, renewable, methane, carbon dioxide
Solar panels – convert sunlight directly into electricity. Sunlight knocks electrons loose from the crystal structure and the loose electrons form an electric current. The amount of power depends on the area of the panel and the light intensity.
Heating for homes – these pipes carry water that absorbs heat energy and transfers it to the house.
Geothermal energy can be used in _______ areas such as ______. In a geothermal source cold water is pumped down towards ____ _____. The water turns to steam and the steam can be used to turn ______. In some areas the _____ rising at the surface can be captured and used directly.
Words – steam, Iceland, volcanic, turbines, hot rocks
A dynamo works by the same principle.
1) How can you make its output bigger?
2) How can you reverse the direction of its output current?
A generator at Drax power station in England
DC stands for “Direct Current” – the current only flows in one direction:
AC stands for “Alternating Current” – the current changes direction 50 times every second (frequency = 50Hz)
Step up transformer
Step down transformer
Electricity reaches our homes from power stations through the National Grid:
If electricity companies transmitted electricity at 240 volts through overhead power lines there would be too much ______ loss by the time electricity reaches our homes. This is because the current is ___. To overcome this they use devices called transformers to “step up” the voltage onto the power lines. They then “____ ____” the voltage at the end of the power lines before it reaches our homes. This way the voltage is _____ and the current and power loss are both ____.
Words – step down, high, power, low, high
Here’s my new shed. I want to connect it to the electricity I my house. Should I use an overhead cable or bury the cable underground?
Voltage across primary (Vp)
No. of turns on primary (Np)
Voltage across secondary (Vs)
No. of turns on secondary (Ns)
Transformers are used to _____ __ or step down _______. They only work on AC because an ________ current in the primary coil causes a constantly alternating _______ ______. This will “_____” an alternating current in the secondary coil.
Words – alternating, magnetic field, induce, step up, voltage
We can work out how much a transformer will step up or step down a voltage:
A 3kW fire left on for 1 hour uses 3kWh of energy
A 1kW toaster left on for 2 hours uses 2kWh
A 0.5kW hoover left on for 4 hours uses __kWh
A 200W TV left on for 5 hours uses __kWh
A 2kW kettle left on for 15 minutes uses __kWh
Electricity is measured in units called “kilowatt hours” (kWh). For example…
To work out how much a device costs we do the following:
Cost of electricity=Power (kW)xtime (h)xcost per kWh (p)
For example, if electricity costs 8p per unit calculate the cost of the following…
60W older bulb, roughly 70p, to be banned in the EU from 2012.
25W “energy efficient” light bulb, £7.30 on Amazon
The POWER RATING of an appliance is simply how much energy it uses every second.
In other words, 1 Watt = 1 Joule per second
E = Energy (in joules)
P = Power (in watts)
T = Time (in seconds)
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