Compare factors affecting induced voltage magnitude
Compare speed, field strength and coil turns while keeping geometry and measurement conditions controlled.
Section P4.5.1 · Electromagnetic induction
Mapped to the named 0654 section using teaching from the corresponding single-science course. A 0654-specific review of every Core and Supplement objective is still in progress. Written practice is self-checked; it does not demonstrate supervised laboratory competence or award an official Cambridge grade.
Before you begin
- Distinguish voltage from current.
- Compare signed readings by absolute magnitude.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
Which reading has the greater magnitude: +0.10 V or −0.25 V?
What you will learn
- Compare speed, field strength and coil turns while keeping geometry and measurement conditions controlled.
- Compare magnitude through controlled changes in speed, field and linked turns, with sign and loading kept separate.
Change the linked field more rapidly
For comparable geometry and motion intervals, moving a magnet or conducting section more quickly changes the linking more rapidly and increases induced e.m.f. magnitude. A stronger field can likewise increase the magnitude for the same movement and arrangement. Stop movement in an otherwise fixed setup and the sustained response disappears.
A coil with more linked turns can give a larger total induced e.m.f. under the same change per turn. This is a statement about the voltage contributions adding, not a guarantee that the measured current rises in the same ratio: more turns can also change resistance and other circuit properties.
Compare one factor and use evidence correctly
Keep the same magnet pole, alignment, movement range and receiver geometry when testing speed. Hold movement and coil setup fixed when testing field strength. For turn comparisons, retain the same change per turn and use suitable voltage measurement or account for detector-circuit changes.
A supplied table of readings can support a qualitative trend, but three measurements do not establish a universal numerical proportionality. Direction reversal changes sign; magnitude comparisons use absolute reading size. No new formula relating field strength and speed is required for this Core objective.
Sources for this lesson
Pause and explain
More turns produce a larger induced e.m.f. Does detector current necessarily rise in the same ratio?
Worked example
Supplied comparable voltage peaks are +0.10 V at slow motion and −0.25 V at faster reversed motion. Compare magnitudes.
Show the worked solution
- Ignore sign only for the magnitude comparison.
- Magnitudes are 0.10 V and 0.25 V.
- The faster trial has the larger peak, while direction also changed.
Answer Faster trial magnitude 0.25 V exceeds 0.10 V; sign records direction separately.
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Choose Easy, Normal or Difficult. Save your answers and open worked review after finishing.
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Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
State three controlled ways to increase induced e.m.f. magnitude in a magnet–coil arrangement.
Give me a hint
Compare the rate of change and linked coil contributions.
Compare my reasoning
- Move the magnet more quickly with path fixed.
- Use a stronger field with motion fixed.
- Use more linked turns with the same change per turn.
Faster movement, stronger field and more linked turns, under matched conditions.
Look for these in your work
- Name all three factors.
- State comparison controls.
Comparable peak readings are −0.12 V, +0.30 V and −0.08 V. Order their magnitudes largest to smallest.
Give me a hint
Use absolute values rather than signed numerical order.
Compare my reasoning
- Magnitudes are 0.12, 0.30 and 0.08 V.
- The largest is 0.30 V.
- Then 0.12 V and 0.08 V.
0.30 V > 0.12 V > 0.08 V.
Look for these in your work
- Use magnitudes.
- Retain voltage units.
Two coils have different turns and resistances. Their detector currents differ. Explain why this alone is insufficient to isolate a turns–e.m.f. relationship.
Give me a hint
Current depends on both driving voltage and circuit resistance.
Compare my reasoning
- Turn count changes the voltage contributions.
- Different receiver resistance also changes current.
- Measure comparable voltage or account for the resistance difference.
The current comparison is confounded by resistance; it does not isolate induced e.m.f. alone.
Look for these in your work
- Name both influences.
- Propose a controlled voltage comparison.
Common mistakes
- Current depends on receiver resistance.
- Magnitude uses absolute value.
- A small data set is not a universal law.
What can you explain now?
What changes can increase coil induced e.m.f. magnitude under otherwise matched conditions?
Compare with the explanation
Faster change, stronger field or more linked turns
Each can increase the induced voltage under the stated controlled comparison.
After trying it yourself, choose your next review. This is your self-assessment.
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Make it stick
Compare magnitude through controlled changes in speed, field and linked turns, with sign and loading kept separate.
If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.