Transmitting Electricity

Learning Objectives Recall the parts of the national grid. Describe what a transformer does. Use the turns ration equation to predict the missing voltage or number of turns.

Question What happens to electricity when it is generated in power stations??

The National Grid All across the UK a network of pylons and cables distribute electricity to our houses.

How are transformers used to supply electricity?

Transformers The voltage of an alternating current can be changed using a transformer. A step-up transformer increases voltage. A step-down transformer decreases voltage.

Why Change Voltage? Voltage is increased as it is transmitted through the national grid. High voltage is very dangerous but reduces energy lost through heat. Voltage is reduced to 230 V before electricity is supplied to homes.

To know how an electric current can be generated in a wire. RULE TO REMEMBER... High = Low = Less energy wasted as Voltage Current heat  

To know how an electric current can be generated in a wire.

To know how an electric current can be generated in a wire. A transformer where the voltage rises is called a step-up transformer

To know how an electric current can be generated in a wire. A transformer where the voltage falls is called a step-down transformer

Direct or alternating current? Because transformers rely on induction (changing fields), they only work with alternating current (a.c.)

The Transformer Equation To know how an electric current can be generated in a wire. The Transformer Equation = Primary voltage Secondary voltage No. of turns on Primary coil No. of turns on Secondary coil or Vp Np = Vs Ns

To know how an electric current can be generated in a wire. Example 1 A transformer has 1000 turns on its primary coil and 3000 turns on its secondary. 30 V is applied across the primary coil. What is its output? V

To know how an electric current can be generated in a wire. Example 2 A transformer has 3800 turns on its primary and 100 turns on its secondary coil. Its output voltage is 6 V. a) Is it a step up or step down transformer? b) Calculate the input voltage. c) Explain why this could be suitable for charging a mobile phone.

a) It is a step down transformer. b) c) Mains voltage is 230V so this transformer is suitable for stepping down the voltage to a safe level for charging a mobile phone. V

Copy and complete the table Vs Ns = Vp Np Copy and complete the table Primary turns Np Secondary turns Ns Primary voltage Vp Secondary voltage Vs Step up or step down 100 20 3 400 10,000 10 50 240 12 5,000 33,000 11,000

Vs Ns = Vp Np Primary turns Np Secondary turns Ns Primary voltage Vp Secondary voltage Vs Step up or step down 100 20 15 3 down 400 10,000 10 250 up 1,000 50 240 12 15,000 5,000 33,000 11,000