Electromagnetism SPL: R. Maisonneuve, Publiphoto Diffusion

What is the motor effect? When a current is passed along a wire in a magnetic field, a force may be exerted on the wire – this is the motor effect. The size of the force is increased if the current or the strength of the magnetic field is increased. The direction of the force is reversed if the direction of the current or the magnetic field is reversed. The direction of the force is at right angles to the direction of the magnetic field and the wire. AQA Science © Nelson Thornes Ltd 2006  2

How does electromagnetic induction work? When a wire cuts the lines of a magnetic field, a potential difference (p.d.) is induced in a wire. If the wire is part of a complete circuit, the induced p.d. causes a current in the circuit. The current is increased if the wire moves faster or a stronger magnet is used. AQA Science © Nelson Thornes Ltd 2006  3

How do transformers work? A transformer consists of two coils of insulated wire (a primary coil and a secondary coil) wrapped on the same iron core. Transformers only work using alternating current. AQA Science © Nelson Thornes Ltd 2006  4

Why are transformers used in the National Grid? The National Grid supplies energy from distant power stations to our homes. For maximum efficiency and minimum energy wastage, the grid p.d. is at least 132 000 V. In your homes the p.d. is 230 V. Transformers are used to step the voltages up or down. AQA Science © Nelson Thornes Ltd 2006  5

What is the transformer equation? Higher What is the transformer equation? p.d. across primary, VP number of turns on primary, NP p.d. across secondary, VS number of turns on secondary, NS = SPL: R. Maisonneuve, Publiphoto Diffusion = AQA Science © Nelson Thornes Ltd 2006  6