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Magnetism & Electromagnetism - Coggle Diagram
Magnetism & Electromagnetism
Magnetism & Electromagnetism
Magnetic Fields
Region where magnetic materials experience a force
Field lines go from North to South
Closer lines = stronger field
Wire field: circular (right-hand rule)
Solenoid field: like a bar magnet (strong & uniform inside)
Permanent & Induced Magnets
Permanent: always magnetic (e.g., bar magnet)
Induced: magnetic only when near another magnet
Magnetic materials: iron, steel, nickel, cobalt
Magnetic Materials
Iron: soft magnetic, easy to magnetise/demagnetise
Steel: hard magnetic, keeps magnetism
Non-magnetic: copper, aluminium, plastic
Electromagnets
Made with: coil of wire + current + iron core
Strength increased by:
More turns
Higher current
Adding soft iron core
Uses of Electromagnets
Scrap yard magnets
MRI machines
Electric bells
Relays
Maglev trains
The Motor Effect
When current flows in a wire in a magnetic field ➝ a force is produced
Fleming’s Left-Hand Rule:
Thumb = Force
First Finger = Field (N ➝ S)
Second Finger = Current (positive ➝ negative)
Max force when wire is perpendicular to field
Electromagnetic Induction
Moving a wire in a magnetic field induces a current
Bigger effect if:
You move the wire faster
Use stronger magnetic field
More coils
Fleming’s Right-Hand Rule for direction
Transformers
Step-up: more secondary turns ➝ increases voltage
Step-down: fewer secondary turns ➝ reduces voltage
Only works with AC
Equations:
Vp / Vs = Np / Ns
Vp × Ip = Vs × Is
Common Exam Mistakes
Forgetting direction of magnetic field lines
Using wrong hand rule
Thinking transformers work with DC ❌
Forgetting how to strengthen electromagnets
Magnetism & Electromagnetism
Magnetic Fields
Magnetic field: Region where a magnetic material or a moving charge experiences a force
Field lines: Show direction and strength (N ➝ S, never cross)
Closer lines = stronger field
Field around a straight current-carrying wire: circular, use Right-Hand Thumb Rule (thumb = current, fingers = field)
Field around solenoid: similar to a bar magnet
Strong and uniform inside coil
Adding an iron core increases field strength (acts as a soft magnetic material)
Permanent & Induced Magnets
Permanent magnets: Always produce their own magnetic field (e.g., bar magnet)
Induced magnets: Become magnetic only when placed in a magnetic field
When field is removed, induced magnet may lose magnetism (temporary)
Magnetic materials: iron, steel, nickel, cobalt
Iron = soft magnetic (magnetises/demagnetises easily)
Steel = hard magnetic (retains magnetism longer)
Electromagnets
Made using: wire coil (solenoid) + current + iron core
Strength depends on:
Number of turns in coil
Size of current
Presence of soft iron core
Magnetic field disappears when current stops
Used in devices that need magnetism to be turned on/off
Uses of Electromagnets
Scrap yard cranes: to lift/attract metal objects
MRI scanners: strong adjustable fields
Electric bells: pull striker toward bell
Relays: act as electromagnetic switches
Maglev trains: levitate and propel using magnetic repulsion
The Motor Effect
A current-carrying conductor in a magnetic field experiences a force
Force is caused by interaction between magnetic field and moving charges
Direction of force: Fleming’s Left-Hand Rule
Thumb = Force (motion)
First finger = Field (North to South)
Second finger = Current (positive ➝ negative)
Force is max when wire is at 90° to field
No force when wire is parallel to field
Electromagnetic Induction
A conductor moving through a magnetic field cuts field lines ➝ induces a voltage (and current if circuit is complete)
Creating current by movement = electromagnetic induction
Increased induced current if:
Move wire faster
Use stronger magnetic field
Use coil with more turns
Fleming’s Right-Hand Rule for direction:
Thumb = motion
First finger = Field
Second finger = Induced current
Transformers
Devices that change voltage of AC using electromagnetic induction
Core made of soft iron (easily magnetised/demagnetised)
Step-up transformer: more turns on secondary coil ➝ higher output voltage
Step-down transformer: fewer turns on secondary ➝ lower voltage
Only works with
AC
(needs changing field)
Equations:
Vp / Vs = Np / Ns
Vp × Ip = Vs × Is (if transformer is 100% efficient)
Common Exam Mistakes
Mixing up direction of magnetic field (N ➝ S, not the other way)
Confusing left-hand and right-hand rules
Saying transformers work with DC (they don’t!)
Forgetting how to strengthen an electromagnet (core, current, turns)
Not using correct equation or rearranging it wrong