P3 Electromagnetism Revision

Electromagnetism How do you make an electromagnet? Insulated wire wrapped round a soft iron core. When current applied a magnetic field is produced.

Electromagnetism How does a scrapyard crane work? Current passed through electromagnet, switches magnet on, steel frame of vehicles attach

Electromagnetism How does a circuit breaker work ? Switch held in place with iron latch, when too much current passes through electromagnet it attracts the iron switch and breaks circuit

Electromagnetism How does an electric bell work? Iron armature is pulled onto the electro magnet, breaks circuit, switching off circuit, releasing armature, cycle repeats

Electromagnetism How does a relay work? Current passes through electromagnet, pulls armature onto electromagnet, armature closes the switch gap and switches on motor.

Electromagnetism What is the motor effect? The force produced when a current in a wire is passed through a magnetic field

Electromagnetism How could you increase the size of the force in the motor effect? Increase the current, increase the size of the magnetic field (bigger magnet).

Electromagnetism Draw Fleming’s Left Hand rule and label the fingers?

Electromagnetism What happens to the force if you reverse the current? You reverse the direction of the force.

Electromagnetism What happens to the force if you reverse the magnetic field? You reverse the direction of the force.

Electromagnetism Describe how a loudspeaker works? Current passes through coil, force moves coil forward, current changes direction, force in opposite direction moves coil back in. Diaphragm vibrates so much sound waves are produced Watch a video

Electromagnetism Why does a loudspeaker work with ac current? The current needs to be changing direction so the force also changes direction. Direct current would make the loudspeaker only move out and stay there.

Electromagnetism Describe how an electric motor works? A current carrying coil rotates in a magnetic field. Force on each side of the coil act in opposite directions. Split ring commutator reverses the current so coil pushed in same direction Watch a video

Electromagnetism What is electromagnetic induction? Process of inducing a voltage using a magnetic field

Electromagnetism How is a voltage induced using a magnetic field? Conductor cuts the lines of a magnetic field, voltage induced across the ends of the conductor Watch a video

Electromagnetism Why are transformers useful? They step up voltage from power stations to reduce energy loss. They also step down voltage so it is safe for consumers. They reduce energy loss.

Electromagnetism How does a transformer work? Alternating current in primary coil induces an alternating magnetic field which induces an alternating voltage in the secondary coils.

Electromagnetism Why do transformers only work with alternating current? You need an alternating current to produce the alternating magnetic field that will induce ac in the secondary coil.

Electromagnetism What is a switch mode transformer?

Electromagnetism Which devices use switch mode transformers? Mobile phone chargers

Electromagnetism In terms of percentages, how efficient are transformers? Almost 100%

Electromagnetism Which equation shows in terms of power that transformers are 100% efficient? V p x I p = V s x I s

Electromagnetism Draw a step up and step down transformer Notice that both of these are 100% efficient because power in = power out