# Electromagnetic Induction Transformers Contents Electromagnetic induction Transformers 1

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Electromagnetic Induction & Transformers Contents Electromagnetic induction Transformers 1 of 32 20 © Boardworks Ltd 2005 2004

Electromagnetic induction What happens if a magnet is moved into a coil of wire? A current is induced in the coil when the magnet is moving. 1 20 2 of 32 © Boardworks Ltd 2005 2004

Stationary magnet What happens when the magnet is inside the coil? Nothing! A current is only induced when the magnet is moving. 1 20 3 of 32 © Boardworks Ltd 2005 2004

Electromagnetic induction What happens if the magnet is moved out of the coil of wire? A current is induced in the coil in the opposite direction. If the direction of movement is reversed, then the direction of the induced current is also reversed. 1 20 4 of 32 © Boardworks Ltd 2005 2004

Inducing current What will happen if a magnet is moved in and out of a coil of wire repeatedly? A current will be induced in the coil. When the magnet is moved into the coil, the current will flow in one direction. Then, when the magnet is moved out of the coil, the direction of the current is reversed and flows in the opposite direction. The induced current is constantly changing direction. What type of current is this? alternating current 1 20 5 of 32 © Boardworks Ltd 2005 2004

Increasing the size of the induced current What are the four ways in which the (induced) current from an AC generator can be increased? faster movement 1. _____________ stronger magnetic field 2. _____________ more coils 3. _____________ larger area of coils 4. _____________ 1 20 6 of 32 © Boardworks Ltd 2005 2004

Electromagnetic Induction & transformers Contents Electromagnetic induction Transformers 1 20 7 of 32 © Boardworks Ltd 2005 2004

Transformers What is a transformer? A device used to increase or decrease voltage. Where are transformers used? In the national grid and household appliances. What do we call a transformer that increases voltage? A step-up transformer. What do we call a transformer that decreases voltage? A step-down transformer. 1 20 8 of 32 © Boardworks Ltd 2005 2004

How does electricity get to your home? power station national grid step-up transformer homes, factories, businesses, etc. 1 20 9 of 32 step-down transformer © Boardworks Ltd 2005 2004

Why are transformers useful? riction is generated When electrical current flows, f______ eat in the conductor which in turn generates h___. This heat is wasted e_____. nergy More wasted energy is oltages than high voltages. created at low v_______ The voltage of the current is increased before it is transferred to the n______ ational g___, rid so that less energy is lost. Then, when the current gets to homes, schools or factories, the voltage is stepped d____. own 1 10 ofof 20 32 © Boardworks Ltd 2005 2004

Which type of transformer? Is this a step-up or a step-down transformer? secondary primary coil This a step-down transformer because there are less turns in the secondary coil than the primary coil. 1 11 ofof 20 32 © Boardworks Ltd 2005 2004

Which type of transformer? Is this a step-up or a step-down transformer? secondary primary coil This a step-up transformer because there are more turns in the secondary coil than the primary coil. 1 12 ofof 20 32 © Boardworks Ltd 2005 2004

Transformer calculations The size of the output voltage from a transformer depends on the ratio of the turns on the primary and secondary coils. This can be calculated using the following formula: V 1 V 2 = N 1 N 2 In this formula, V is the voltage in a coil and N is the number of turns in that coil. 1 13 ofof 20 32 © Boardworks Ltd 2005 2004

Transformer question (1) A transformer has 200 turns on its primary coil and 50 turns on its secondary coil. The input voltage is 920 V. • Is this a step-up or step-down transformer? step-down • What is the output voltage? V 2 V 1 = V 2 = = 1 14 ofof 20 32 N 1 N 2 x V 1 N 1 50 x 920 200 230 V © Boardworks Ltd 2005 2004

Transformer question (2) A transformer has 100 turns on its primary coil. It has an input voltage of 35 V and an output voltage of 175 V. • Is this a step-up or step-down transformer? step-up • How many turns are on the secondary coil? N 2 N 1 = N 2 = = 1 15 ofof 20 32 V 1 V 2 x N 1 V 1 175 x 100 35 500 turns © Boardworks Ltd 2005 2004