⚡Permanent Magnet Active: Strength 60 mT. Red represents
North; Blue is South.Drag magnet through coil bore
📋
Observation Data Logger
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Coil Setup
Loops (N)
Velocity (cm/s)
Flux Φ (μWb)
Induced EMF E (V)
Current I (mA)
Bulb Power P (mW)
📘 Faraday's Law & Induction Guide
What is Faraday's Law of Electromagnetic Induction?
In 1831, Michael Faraday discovered that an electric current can
be induced in a closed circuit whenever the magnetic flux linking
the circuit changes over time.
This physical principle underpins modern electrical engineering,
powering electric generators, transformers, induction motors,
wireless chargers, and magnetic levitation trains.
Key Physical Realizations
Magnetic Flux: The total number of magnetic
field lines passing through a given area.
Relative Motion: An EMF is only induced while
the magnet is in motion relative to the coil; when the magnet
stops moving, the induced EMF instantly drops to zero!
Lenz's Law: The induced electromotive force
always acts in such a direction as to oppose the change in
magnetic flux that produced it (conservation of energy).
Fundamental Equations (Class 9–12 Physics)
1. Magnetic Flux (Φ):
Φ = B · A · cos(θ) [Webers (Wb)]
Where B is magnetic flux density (Tesla), A is coil area (m²), and
θ is the angle between magnetic field and area normal.
2. Faraday's Law of Induction:
E = -N · (dΦ / dt) [Volts (V)]
Where N is the number of coil turns, and (dΦ/dt) is the time rate
of change of magnetic flux.
3. Motional EMF in a Conductor:
E = B · l · v [Volts (V)]
Where l is the length of conductor moving at velocity v
perpendicular to magnetic field B.
4. Induced Circuit Current & Electric Power:
I = E / R [Amperes (A)]
P = I² · R = E² / R [Watts (W)]
Interactive Controls & Manipulation
Drag Bar Magnet: Click and drag the bar magnet
horizontally into or out of the coil loops to observe real-time
induction.
Flip Magnet Polarity: Click the "⇄ Flip Magnet
Polarity" button to invert the North and South magnetic poles.
Notice how the induced EMF and electron drift direction reverse!
Turns Count (N): Change coil turns from 1 to 4
loops. Notice that 4 turns produce twice the induced EMF of 2
turns under identical speed.
Display Toggles: Toggle magnetic field lines,
electron drift animations, and field sensor readout.
Recommended Interactive Investigations
Experiment 1: Stationary Magnet vs Moving Magnet
Place the magnet right inside the coil and hold it completely
still. Note that the induced EMF reads 0.00 V and the bulb does
not glow! Move it suddenly to produce instant illumination.
Experiment 2: Dependence on Velocity
Push the magnet through slowly, then flick it through rapidly.
Observe how higher velocity (dx/dt) produces a dramatically
larger EMF and radiant bulb brightness.
Experiment 3: Verification of Lenz's Law
Push the North pole into the coil from the left. Observe the
positive induced EMF and current direction. Now pull the North
pole out to the left; the induced current immediately reverses
direction!
Experiment 4: Turn Scaling (2 vs 4 Turns)
Switch to Dual Coils and compare the peak voltage achieved
through the 2-turn coil versus the 4-turn coil at the same
speed.
Frequently Asked Questions
Q: Why is there a negative sign in Faraday's equation (E = -N
dΦ/dt)?
A: The negative sign represents Lenz's Law, ensuring that energy
is conserved. If the sign were positive, induced currents would
reinforce the changing flux, creating infinite free energy, which
violates the First Law of Thermodynamics.
Q: Why does the bulb glow brightly during both entry and exit
of the magnet?
A: The bulb's power is proportional to E² (P = E² / R). Because
squaring eliminates the negative sign, electrical power is
dissipated as light and heat regardless of which direction the
current is flowing.
Q: Why does the induced EMF reverse when pulling the magnet
out?
A: According to Lenz's Law, when a magnetic pole recedes, the coil
produces an attractive opposing field. This reverses the sign of
(dΦ/dt) and flips the direction of the induced electromotive
force.
📐 Mathematical Physical Derivation
Calculated Physical Solution
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Challenge Completed!
🎉
Outstanding work! You have successfully matched the experimental
parameters.
