IEB PHYSICAL SCIENCES / PHYSICS E · ELECTRODYNAMICS
PHYSICAL SCIENCES / PHYSICS
ELECTRODYNAMICS
IEB study notes | Magnetism, motors, induction, generators, transformers &
AC
THE BIG IDEA
Electricity and magnetism are closely linked. Electric currents create magnetic fields. Magnetic fields
can exert forces on current-carrying wires, allowing motors to turn. A changing magnetic field through
a coil can produce a voltage, allowing generators and transformers to work.
HOW TO USE THESE NOTES
FEATURE HOW TO STUDY
Official IEB definition Memorise the provided wording exactly.
Understand it Focus on the physical reason behind the rule.
Diagram Use the drawing to determine direction or recognise a device.
Worked example Practise the standard examination method.
Difficult / exception Check a misconception or an unusual condition.
Practise your intuition Make your own prediction before viewing the answer.
Enrichment knowledge Useful background beyond the minimum SAG requirements.
QUICK SYMBOL GUIDE
⊙ means out of the page (towards you); ⊗ means into the page (away from you). B is magnetic flux
density, Φ is magnetic flux, N is number of turns, and emf is induced voltage. Learn one idea at a time.
Core knowledge · Exam definitions · Visual explanations · Practice 1
, IEB PHYSICAL SCIENCES / PHYSICS E · ELECTRODYNAMICS
1 ELECTROMAGNETISM
1.1 What is a magnetic field?
A magnetic field is a region where magnets, magnetic materials or moving electric charges can
experience magnetic effects. Permanent magnets have magnetic fields, and electric currents also
produce magnetic fields.
CORE IEB FACT
A magnetic field exists around a permanent magnet or a current-carrying conductor.
Field lines are imaginary lines that show the direction of the field. The direction at a point follows the
line’s arrow. Closer field lines indicate a stronger field. They never cross. Outside a bar magnet, field
lines run from north to south; inside the magnet they return from south to north.
1.2 Straight current-carrying wire
Around a straight wire the magnetic field forms circles centred on the wire. Use the right-hand grip
rule: point your right thumb in the direction of conventional current; your curled fingers show the
direction of the circular magnetic field.
Current OUT of page (dot = arrow tip)
Field anticlockwise: right-hand thumb out of page
View looking along the wire: dot = current towards the reader, so the field is anticlockwise.
Current INTO page (cross = arrow tail)
Field clockwise: right-hand thumb into page
Cross = current away from the reader; reverse the current and the field reverses.
Core knowledge · Exam definitions · Visual explanations · Practice 2
PHYSICAL SCIENCES / PHYSICS
ELECTRODYNAMICS
IEB study notes | Magnetism, motors, induction, generators, transformers &
AC
THE BIG IDEA
Electricity and magnetism are closely linked. Electric currents create magnetic fields. Magnetic fields
can exert forces on current-carrying wires, allowing motors to turn. A changing magnetic field through
a coil can produce a voltage, allowing generators and transformers to work.
HOW TO USE THESE NOTES
FEATURE HOW TO STUDY
Official IEB definition Memorise the provided wording exactly.
Understand it Focus on the physical reason behind the rule.
Diagram Use the drawing to determine direction or recognise a device.
Worked example Practise the standard examination method.
Difficult / exception Check a misconception or an unusual condition.
Practise your intuition Make your own prediction before viewing the answer.
Enrichment knowledge Useful background beyond the minimum SAG requirements.
QUICK SYMBOL GUIDE
⊙ means out of the page (towards you); ⊗ means into the page (away from you). B is magnetic flux
density, Φ is magnetic flux, N is number of turns, and emf is induced voltage. Learn one idea at a time.
Core knowledge · Exam definitions · Visual explanations · Practice 1
, IEB PHYSICAL SCIENCES / PHYSICS E · ELECTRODYNAMICS
1 ELECTROMAGNETISM
1.1 What is a magnetic field?
A magnetic field is a region where magnets, magnetic materials or moving electric charges can
experience magnetic effects. Permanent magnets have magnetic fields, and electric currents also
produce magnetic fields.
CORE IEB FACT
A magnetic field exists around a permanent magnet or a current-carrying conductor.
Field lines are imaginary lines that show the direction of the field. The direction at a point follows the
line’s arrow. Closer field lines indicate a stronger field. They never cross. Outside a bar magnet, field
lines run from north to south; inside the magnet they return from south to north.
1.2 Straight current-carrying wire
Around a straight wire the magnetic field forms circles centred on the wire. Use the right-hand grip
rule: point your right thumb in the direction of conventional current; your curled fingers show the
direction of the circular magnetic field.
Current OUT of page (dot = arrow tip)
Field anticlockwise: right-hand thumb out of page
View looking along the wire: dot = current towards the reader, so the field is anticlockwise.
Current INTO page (cross = arrow tail)
Field clockwise: right-hand thumb into page
Cross = current away from the reader; reverse the current and the field reverses.
Core knowledge · Exam definitions · Visual explanations · Practice 2
