P1H Smart Lesson 4

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

Write Down Transformers are devices that can change the size of A.C. voltages – they cannot be used to change D.C. voltages.

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

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.

? = 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 12 100 Vs = 10 x 12 = 12 volts

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

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

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