Y9 Physics - Magnetism/Electromagnetism markscheme tips

How a loudspeaker works

Current flows through the coil, the coil gets magnetised, magnetic fields of the coil and permanent magnet interact, resultant magnetic force pushing cone and solenoid, if current direction reverses then cone reverses, amplitude of cone (loudness) depends on strength of current, frequency of cone (pitch) depends on how often current reverses. Causes variations in air pressure and causes air particles to oscillate (about fixed positions) creating longitudinal sound waves

How an electromagnet works

Switch closed, current flows in the coil, coil becomes magnetised, core becomes magnetised (if relevant)

How a relay circuit works

Current flows in the low-current control circuit. Electromagnet becomes magnetised. Iron armature moves to close contacts. This allows higher voltage circuit to work and connects lower voltage circuit to higher voltage circuit

How an electric bell works

Switch closed, current flows through the coil, coil and core becomes magnetised creating electromagnet, electromagnet’s magnetic field attracts iron armature, hammer attached to armature hits bell, contact points lose contact, spring pulls armature back so that contact points make contact again, cycle repeats

Ways to increase magnetic force exerted by an electromagnet

Increase current, increase number of coils, add a soft iron core

How to plot a magnetic field

Place the magnet on paper, draw around the magnet, place the compass at the North Pole, place a dot where the north seeking pole is pointing, move thé magnetic compass so that the end of the South seeking pole is at that dot, repeat until you reach the South Pole, draw a line over these dots, repeat from different points of the North Pole, ADD ARROWS POINTING FROM NORTH TO SOUTH