IP Physics Notes (Upper Secondary, Year 3-4): 15) Electromagnetism

Study guide30 Sep 2025, 00:00 ZUpdated 30 Nov 2025

Map current-generated fields, magnetic forces, and the DC motor cycle for integration into IP problem solving.

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Q: What does IP Physics Notes (Upper Secondary, Year 3-4): 15) Electromagnetism cover?
A: Map current-generated fields, magnetic forces, and the DC motor cycle for integration into IP problem solving.

Quick recap -- Electric currents create magnetic fields, and those fields can push on other currents or moving charges. Use the right-hand grip to sketch fields and Fleming's left hand to predict the resulting forces.

The core idea is simple: Current can create magnetic fields, and magnetic fields can push current.

Use it as a working check: Use right-hand grip for fields around wires and solenoids. Use Fleming's left hand for force direction in motors and current-carrying conductors.

Then go one layer deeper: Work through solenoids, relays, force direction, and the DC motor cycle to practise linking field direction, current direction, and motion in one diagram.

Keep your practice loop tight via our IP Physics tuition hub-it links each topic here to quizzes, diagnostics, and WA-style problem sets.

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These notes align with SEAB GCE O-Level Physics (6091) content used in IP programmes (exams from 2026).

Status: SEAB O-Level Physics 6091 syllabus (exams from 2026) checked 2025-11-30 - scope unchanged; remains the reference for these notes.

Magnetic Effect of a Current

Straight wire: concentric circular field lines; use right-hand grip rule $\text{thumb} = \text{current, curled fingers} = \text{field direction}$

Reviewed by

Chee Wei Jie·Academic Advisor (Physics)

Given in the question	What to label first	What changes the force?	Common trap
Bar magnet poles	Field direction from north to south	Reversing the poles reverses force	Drawing field from south to north
Conventional current arrow	Current direction in the wire	Reversing the supply reverses force	Using electron flow when the question expects conventional current
Both field and current reversed	New field and new current both flip	Force stays in the original direction	Reversing the force twice without noticing
Wire parallel to field	Current is not cutting field lines	No sideways force in this ideal case	Applying Fleming's left hand when the three directions cannot be perpendicular

Diagram symbol	Meaning	How to use it	Common trap
Dot, $\odot$	Direction out of the page, towards you	Treat it as the current or field arrow pointing out of the paper.	Reading it as a positive charge rather than a direction symbol.
Cross, $\otimes$	Direction into the page, away from you	Treat it as the current or field arrow pointing into the paper.	Reversing dot and cross because both look like marks on the page.
Magnetic field from N to S	Field direction across the gap	Point Fleming's first finger from north pole to south pole.	Using the force direction as if it were the field direction.
Conventional current	Current from positive to negative terminal	Point Fleming's second finger in the current direction given by the circuit.	Using electron flow unless the question explicitly asks for it.

Moment in the rotation	What happens to the coil side	What the split-ring commutator does	Result
First half turn	Left and right sides experience opposite forces.	Each half-ring connects one coil end to one brush.	The coil starts rotating.
Just past the vertical position	The side that was on the left moves to the right.	The split ring swaps which brush each coil end touches.	Current in each side reverses.
Next half turn	The side is now in the opposite field position.	Reversed current combines with the changed position.	Force direction on each physical side reverses, but the torque still turns the coil the same way.

IP Physics Notes (Upper Secondary, Year 3-4): 15) Electromagnetism

Magnetic Effect of a Current

Applications of Current-Produced Fields

Force on a Current-Carrying Conductor

Fleming setup checkpoint

Dot-cross direction checkpoint

Force on Moving Charges

DC Motor Essentials

DC motor half-turn checkpoint

Worked Example: Predicting Motor Rotation

Practice Quiz

Key Takeaways

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