Electromagnetic Induction & Transformers Contents Electromagnetic induction Transformers

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.

Stationary magnet What happens when the magnet is inside the coil? Nothing! A current is only induced when the magnet is moving.

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.

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

Increasing the size of the induced current What are the four ways in which the (induced) current from an AC generator can be increased? 1. _________________________ 2. _________________________ 3. _________________________ 4. _________________________ faster movement stronger magnetic field more coils larger area of coils

Electromagnetic Induction & transformers Contents Electromagnetic induction Transformers

Transformers What is a transformer? Where are transformers used? What do we call a transformer that increases voltage? What do we call a transformer that decreases voltage? A device used to increase or decrease voltage. In the national grid and household appliances. A step-up transformer. A step-down transformer.

How does electricity get to your home? power station national grid step-up transformer homes, factories, businesses, etc. step-down transformer

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

Which type of transformer? Is this a step-up or a step-down transformer? primary coil secondary coil This a step-down transformer because there are less turns in the secondary coil than the primary coil.

Which type of transformer? Is this a step-up or a step-down transformer? primary coil secondary coil This a step-up transformer because there are more turns in the secondary coil than the primary coil.

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: V1 N1 V2 N2 = In this formula, V is the voltage in a coil and N is the number of turns in that coil.

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? What is the output voltage? step-down V2 N2 V1 N1 = N2 N1 = V2 x V1 50 200 = V2 x 920 = 230 V

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? How many turns are on the secondary coil? step-up N2 V2 N1 V1 = V2 V1 = N2 x N1 175 35 = N2 x 100 = 500 turns