“Transformers – Roberts in disguise” Core Physics – Energy Exam Date - “Transformers – Roberts in disguise” L/O :- To understand how electricity can be transported by the national grid from power stations to homes

Quick Quiz - What do you remember from last lesson? What are the pros and cons of nuclear energy? How does a coal power station turn the turbine to spin the generator? What is the equations for working out efficiency? How do you work out the pay-back time for insulation? What are the pros and cons of wind energy? How do storage heaters work? What happens to wasted energy? How does evaporation help to cool things down? What are the pros and cons of solar energy When is solar energy usually used?

Why can birds sit on high voltage cables? 24/04/2017 Why can birds sit on high voltage cables?

Electricity reaches our homes from power stations through the The National Grid 24/04/2017 Electricity reaches our homes from power stations through the National Grid: Power station Step up transformer Step down transformer Homes Our houses use electricity at 230 volts But if the electricity company transported through the power lines at 230 volts they would lose lots of energy as heat because the current would be too high To prevent this energy loss they use Transformers.

Use the transformers to work out how they affect voltage and current 24/04/2017 Use the transformers to work out how they affect voltage and current Where should the national grid use each type of transformer? How reproducible is your data? How could you improve it?

Step down transformers 24/04/2017 Step up transformers These have MORE coils on the second side and increase the voltage and decrease the current Step down transformers These have LESS coils on the second side and decrease the voltage and increase the current

Step down transformers 24/04/2017 Step up transformers The national grid use “step- up” transformers to increase the voltage and decrease the current before it goes into the power cables so less energy is lost Step down transformers The national grid use “step-down” transformers to reduce the voltage before it gets into our houses. This is important for safety.

Words – induce, step up, voltage Transformers 24/04/2017 Transformers are used to _____ __ or step down _______. They only work on AC because an Alternating current in the primary coil causes a constantly alternating Magnetic Field. This will “_____” an alternating current in the secondary coil. Words – induce, step up, voltage We can work out how much a transformer will step up or step down a voltage: Voltage across primary (Vp) No. of turns on secondary (Ns) Voltage across secondary (Vs) No. of turns on primary (Np)

Some transformer questions 24/04/2017 Primary voltage Vp Secondary voltage Vs No. of turns on primary Np No. of turns on secondary Ns Step up or step down? 12V 24V 100 ? 400V 200V 20 25,000V 50,000V 1,000 23V 230V 150

Some example questions 24/04/2017 Primary voltage Vp Secondary voltage Vs No. of turns on primary Np No. of turns on secondary Ns Step up or step down? 6V 24V 100 ? 400,000V 200V 1,000 25,000V 20,000 20 230V 150 1,500 A transformer increases voltage from 10V to 30V. What is the ratio of the number of turns on the primary coil to the number of turns on the secondary coil? A step-down transformer has twice as many turns on the primary coil than on the secondary coil. What will be the output (secondary) voltage if the input voltage is 50V?

What have you learnt? What is a transformer? What affect do step-up transformers have on the voltage and current? What affect do step-down transformers have on the voltage and current? How do the national grid use step-up and step-down transformers