What do all these have in common What

Transformers Learning Outcomes By the end of this lesson you will be able. .

• Electricity is transferred from power stations to homes through the wires and

• To reduce these losses, the National Grid transmits electricity at a low

Power station 25, 000 V Step up Step down transformer National grid transformer cables

The Transformer Principle AIM: To investigate how the output voltage of a transformer depends

The Transformer Principle Primary coil with 30 turns 2 V V Secondary coil with

The Transformers Principle Primary Turns Secondary Turns Input Voltage / V 30 10 2.

The Transformer principle • State the independent, and all the control variables (remember this

The Transformer principle Extra challenge: For transformers, which are 100% efficient, the output voltage

The Transformer principle • If the output voltage is less than the calculated voltage,

Applications of transformers A step up transformer increases the voltage (Point up) A step

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What do all these have in common? What are they used for? 1

Transformers Learning Outcomes By the end of this lesson you will be able. . . To investigate practically how a transformer works. To identify some applications of transformers. Keywords Transformer, step-up, step-down , c-core 2

• Electricity is transferred from power stations to homes through the wires and cables of the National Grid. • When a current flows through a wire some energy is lost as heat. The higher the current, the more heat is lost. 4

• To reduce these losses, the National Grid transmits electricity at a low current. This needs a high voltage. • Power = voltage x current • Power stays the same so. . • Power = voltage x current 5

Power station 25, 000 V Step up Step down transformer National grid transformer cables and wires 400, 000 V Homes and Schools 230 V 6

The Transformer Principle AIM: To investigate how the output voltage of a transformer depends upon the number of turns on the secondary coil. APPARATUS • Electrical power supply set at 2 V A. C. • Connecting wires • An A. C. multimeter (to measure the voltage) • Iron C-core with primary coil of 30 turns of wire on it. • Various iron C-cores with 10, 20, 30, 40, 50 and 60 turns of wire • Calculator 7

The Transformer Principle Primary coil with 30 turns 2 V V Secondary coil with 10, 20, 30, 40, 50 or 60 turns C-cores V SAFETY Always switch off the power supply before making any changes to the circuit. 8

The Transformers Principle Primary Turns Secondary Turns Input Voltage / V 30 10 2. 0 Output Voltage /V Expected Output Voltage /V Leave this column for now 9

The Transformer principle • State the independent, and all the control variables (remember this from IAAs). • Plot a graph of output voltage (V) (y-axis) against number of turns on secondary coil (xaxis). • Describe how the output voltage depends on the number of turns on the secondary 10

The Transformer principle Extra challenge: For transformers, which are 100% efficient, the output voltage can be calculated using this equation. • Use this equation to calculate the expected output voltage (empty column on the table) • How does these answers compare with your results? 11

The Transformer principle • If the output voltage is less than the calculated voltage, the transformer is less than 100% efficient. • Come up with ideas why this may be. 12

Applications of transformers A step up transformer increases the voltage (Point up) A step down transformer decreases the voltage (Point down) Decide whether you think the following are step up transformers or step down transformers. Extra challenge: Explain why. 13

Lap top charger 14

X ray machine 15

Phone charger 16

National Grid 17

Can you think of any other examples? 18