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P1H Smart Lesson 4
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DC and AC 18/04/2016 Write Down V DC stands for “Direct Current” – the current only flows in one direction: Time 1/50th s AC stands for “Alternating Current” – the current changes direction 50 times every second (frequency = 50Hz) 230V T V
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Write Down Transformers are devices that can change the size of A.C. voltages – they cannot be used to change D.C. voltages.
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Words – step down, high, power, low, high
The National Grid Electricity reaches our homes from power stations through the National Grid: Power station Step up transformer Step down transformer Homes Write Down 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
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Write Down Transformers only produce an output voltage when the input voltage is constantly changing. When it is changing the following equation can be used for transformer calculations.
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? = 300 12 100 Vs = 10 x 12 = 12 volts This is 10 times bigger on top
SO Vs must be 10 times bigger than Vp ? = 300 Vs = 10 x 12 = 12 volts
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Power is the energy transferred (also known as Work Done) per second
Power is measured in watts, which is also known as joules per second (j/s) Write Down
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Non-renewable energy sources
18/04/2016 Write Down Advantages Disadvantages Pollution – CO2 leads to global warming and SO2 leads to acid rain Cheap fuel costs Coal, oil, gas and nuclear Generate a lot of energy Fuel will run out Easy to use
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Renewable energy sources
18/04/2016 Write Down Advantages Disadvantages Often depend on the weather – is it sunny??? Clean Wind, tidal, solar etc Won’t run out Look ugly Energy is “dilute” – in other words, it’s very spread out Easily accessible
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