Q: What does IP Physics Notes (Upper Secondary, Year 3-4): 16) Electromagnetic Induction cover? A: Apply Faraday and Lenz, sketch AC generator waveforms, and compute transformer ratios for power transmission questions.
Quick recap -- Changing magnetic flux induces emf. Remember: faster change -> larger emf, and the induced current always opposes the flux change (Lenz). Generators and transformers are direct applications.
The core idea is simple: Induction happens when magnetic flux changes.
Use it as a working check: Faster motion, stronger magnets, or more coil turns increase induced emf. Lenz's law says the induced current opposes the change that caused it.
Then go one layer deeper: Use the generator and transformer sections to practise explaining flux change, predicting polarity, sketching AC output, and applying voltage-turns ratios.
Keep your practice loop tight via our Sec 4 IP Physics tuition hub. It links each topic here to quizzes, diagnostics, and WA-style problem sets.
For Integrated Programme students: Your current school materials, teacher instructions, and assessment scope take precedence because IP topic sequence and depth vary by school. This is an Eclat IP guide, not the O-Level / SEC G3 exam-track guide.
Faraday: magnitude of induced emf E is proportional to rate of change of magnetic flux linkage.
Lenz: induced current direction opposes the change producing it (conservation of energy).
Practical consequences:
Move magnet faster -> larger E.
Use stronger magnet or more coil turns -> larger E.
No change in flux -> no induction.
Induction Setups
Pushing/pulling magnet through coil.
Moving a conductor across magnetic field lines.
Rotating a coil in a uniform magnetic field (basis of AC generator).
Use right-hand grip rule to infer the induced polarity that opposes the motion (e.g., approaching north pole induces north on near face of coil).
Lenz direction checkpoint
Before choosing a current direction, name the change first. The induced current is chosen to oppose that change, not to copy the magnet's motion.
Situation
Flux change to name first
Induced face needed
Common trap
North pole moves towards coil
North-going flux through coil increases
Near face becomes north to repel the approach
Saying "opposes the magnet" without naming the increasing flux
North pole moves away from coil
North-going flux through coil decreases
Near face becomes south to attract it back
Using the same current direction as the approach case
South pole moves towards coil
South-going flux through coil increases
Near face becomes south to repel the approach
Forgetting that the pole label flips but the opposition idea stays
Magnet held still inside coil
Flux is not changing
No induced emf or current
Thinking a strong magnet alone is enough for induction
Misconception check: Lenz's law opposes the change in flux, not the existence of flux. A stationary magnet can give a strong flux but still produce no induced current.
Alternating-Current Generator
Coil rotates in magnetic field; flux linkage varies sinusoidally.
Slip rings maintain continuous connection; output is AC.
Peak emf depends on rotation speed, flux density, and coil turns.
Voltage-time graph: sine wave crossing zero twice per revolution; faster rotation increases frequency.
Generator graph checkpoint
For generator questions, connect coil orientation to rate of flux change before sketching the voltage-time graph.
coil position
-> flux through coil
-> rate of flux change
-> induced emf size and sign
Coil moment
Flux through coil
Rate of change
Graph cue
Coil face is broadside to the field
Maximum or minimum flux
Momentarily zero
Emf crosses zero.
Coil face is edge-on to the field
Flux passes through zero
Greatest rate of change
Emf has maximum magnitude.
Half a turn later
Same orientation but opposite side leading
Same magnitude, opposite direction
Emf has opposite sign.
Faster rotation
Flux pattern repeats more quickly
Greater rate of change
Higher peak emf and higher frequency.
Worked check: if a coil rotates twice as fast in the same magnetic field, the graph completes cycles twice as often. The peak emf also increases because the flux changes faster, not because the maximum flux through the coil has become larger.
Misconception check: maximum flux and maximum emf do not occur at the same instant. Emf depends on how quickly flux is changing, so it is zero when the flux is momentarily at a maximum or minimum.
Transformers
Two coils wound on common soft-iron core; only works with AC (changing flux required).
Step-up: Ns>Np -> voltage increases, current decreases.
Step-down: Ns<Np
Real transformers suffer losses:
Copper loss: I2R heating; mitigated with low-resistance windings.
Eddy currents: reduced via laminated cores.
Hysteresis: reduced by soft iron core.
Flux leakage: minimised by tight coupling between coils.
Transformer setup checkpoint
Before substituting into the transformer equations, label the input side, output side, and whether voltage is stepping up or down. This keeps the turns ratio and current change tied to the same physical story.
Question clue
First label
Equation move
Trap to avoid
Supply is connected to one coil
That coil is the primary, p.
Put its voltage and turns under Vp and Np.
Calling the lower-voltage side "primary" just because it is safer.
More turns on secondary
Step-up transformer
Ns>Np, so Vs>Vp
Fewer turns on secondary
Step-down transformer
Ns<Np, so Vs<Vp
Ideal transformer power is assumed
Input power equals output power
Use VpIp=VsIs
Worked check: if Np=200, Ns=1000, and Vp=12V, then the transformer is step-up because the secondary has more turns. The output voltage is
Vs=VpNpNs=12×2001000=60V.
Misconception check: a transformer does not create extra power. If the ideal output voltage is five times larger, the output current is five times smaller for the same transferred power.
Worked Example: Step-Down Calculation
The primary voltage is
11kV,Np=3,300,Ns=110
The secondary voltage is
Vs=Vp(Ns/Np)=11,000×110/3,300≈3.67×102V
Assuming ideal behaviour,
Is=P/Vs≈2.73×102A
so the primary current is
Ip=IsVs/Vp≈9.2A
Power Transmission Rationale
Power delivered: P=VI.
Transmission loss in cables: Ploss=I2Rcable.
Step-up to high voltage -> smaller current -> dramatically lower I2R losses.
Step-down near consumers for safe household voltages.
Practice Quiz
Step through flux-change scenarios, generator waveforms, and transformer calculations in this induction checkpoint.
Key Takeaways
Identify flux changes: moving magnet/coil, changing area, changing field strength.
Lenz's law gives induced current direction; the induced field always resists the cause.
Transformers rely on AC; memorise ratio equations and common loss-reduction techniques.
In transmission questions, emphasise "high voltage -> low current -> reduced I2R losses" to justify design choices.
-> voltage decreases, current increases.
.
Increasing both voltage and current in an ideal transformer.
.
Reversing the ratio and getting a larger output voltage.
.
Forgetting that higher voltage means lower current for the same power.
