IGCSE 0625 · ELECTRICITY & MAGNETISM · 4.5

Electromagnetic effects

The magnetic effect of a current, the force on a conductor and the motor, electromagnetic induction and the generator, and transformers and the grid. It brings magnetism and electricity together to run the modern world.

TOPIC 4.5: ELECTROMAGNETIC EFFECTS CAMBRIDGE IGCSE PHYSICS 0625 · PATHWAYS TheLucidSTEM · thelucidstem.com BUILDS ON 4.1 Magnetism 4.2 Electrical quantities LEADS TO The power grid Motors & generators ELECTRO- MAGNETISM 1 · MAGNETIC EFFECT OF A CURRENT An electric current always makes a magnetic field around it. The field circles a straight wire. A coil (solenoid) makes a field like a bar magnet. More turns, more current, or an iron core make it stronger. Used in electromagnets, relays, and loudspeakers. N S a solenoid acts like a bar magnet 2 · FORCE ON A CONDUCTOR A current-carrying wire in a magnetic field feels a force. Fleming's left-hand rule gives the direction. Reverse the current or the field and the force reverses too. A d.c. motor spins a coil using a split-ring. N S force current out field N → S 3 · INDUCTION & THE GENERATOR Moving a magnet near a coil induces an EMF. A changing field through the coil makes a voltage; faster motion gives more. Reverse the motion and the EMF reverses. An a.c. generator spins a coil between magnets and takes current off through slip rings. N S move G the meter shows the induced current 4 · TRANSFORMERS & THE GRID A changing current in one coil induces a voltage in another coil on the same core. Vₚ / Vₛ = Nₚ / Nₛ (Extended) Step-up raises voltage; step-down lowers it. The grid sends power at very high voltage so the current is small and little is lost as heat in the cables. primary secondary more turns on the secondary raises V
TOPIC 4.5: ELECTROMAGNETIC EFFECTS CAMBRIDGE IGCSE PHYSICS 0625 · PATHWAYS TheLucidSTEM · thelucidstem.com BUILDS ON 4.1 Magnetism 4.2 Electrical quantities LEADS TO The power grid Motors & generators ELECTRO- MAGNETISM 1 · MAGNETIC EFFECT OF A CURRENT An electric current always makes a magnetic field around it. The field circles a straight wire. A coil (solenoid) makes a field like a bar magnet. More turns, more current, or an iron core make it stronger. Used in electromagnets, relays, and loudspeakers. N S a solenoid acts like a bar magnet 2 · FORCE ON A CONDUCTOR A current-carrying wire in a magnetic field feels a force. Fleming's left-hand rule gives the direction. Reverse the current or the field and the force reverses too. A d.c. motor spins a coil using a split-ring. N S force current out field N → S 3 · INDUCTION & THE GENERATOR Moving a magnet near a coil induces an EMF. A changing field through the coil makes a voltage; faster motion gives more. Reverse the motion and the EMF reverses. An a.c. generator spins a coil between magnets and takes current off through slip rings. N S move G the meter shows the induced current 4 · TRANSFORMERS & THE GRID A changing current in one coil induces a voltage in another coil on the same core. Vₚ / Vₛ = Nₚ / Nₛ (Extended) Step-up raises voltage; step-down lowers it. The grid sends power at very high voltage so the current is small and little is lost as heat in the cables. primary secondary more turns on the secondary raises V
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