Pick a topic, read the steps, then try them right in the sandbox below.
Class 12 — Electric field and potential around charges
Concept: field lines point away from positive charges and into negative
ones; potential is highest near a positive charge and lowest near a negative one, and
both fall off with distance.
- Switch to Electrostatics mode.
- Drag the small grey probe close to a positive charge and note Field |E| at
probe and Potential V at probe — both should be large.
- Drag the probe far from both charges — both readings should shrink toward zero.
- Flip one charge's sign (if a control is available) or drag the probe exactly
between two equal-and-opposite charges — the field lines should visibly curve from
the positive charge straight into the negative one.
Takeaway: field lines are a picture of force direction, while
potential is a single number describing the "electrical height" at a point.
Class 12 — Electromagnetic induction and Lenz's law
Concept: moving a magnet through a coil changes the magnetic flux through
it, and that changing flux induces an EMF: ε = −N dΦ/dt. The minus
sign is Lenz's law — the induced current always opposes the change that caused it.
- Switch to Induction mode.
- Set an Oscillation freq. and watch the magnet swing through the coil.
Watch Flux Φ rise and fall, and EMF ε=-NdΦ/dt spike
each time the flux is changing fastest (as the magnet passes through the coil).
- Note the Induced current direction flips depending on whether the magnet
is approaching or receding — that sign flip is Lenz's law in action.
- Raise Coil turns N and watch the EMF spikes grow taller for the same
magnet motion.
Takeaway: EMF depends on how fast the flux changes, not on the flux
itself — that's why the EMF peaks exactly when the magnet is moving through the coil,
not when it's sitting still inside it.
Class 12 — Motional emf and Lenz's law
Concept: a rod moving across a magnetic field has an emf ε = BLv induced in it. The current this drives is acted on by a
force that opposes the motion (Lenz's law), and the lost kinetic energy becomes heat.
- Open Motional emf: B = 0.8 T, L = 0.5 m, R = 2 Ω, m = 0.4 kg, starting speed 4 m/s. ε = BLv = 1.6 V, I = ε ÷ R = 0.8 A, and the braking
force is BIL = 0.32 N. The current flows anticlockwise.
- With no pull the rod slows down exponentially: v = v0e−t/τ with τ = mR ÷ B2L2 = 5 s. After 1 s the speed is 3.27 m/s. It
slides 20 m in total.
- The power turned into heat at the start is εI = 1.28 W, equal to the braking force times the speed (0.32 × 4).
- Add a steady pull of 2 N: the rod settles at the terminal speed vt = FR ÷ B2L2 = 25 m/s, where the pull equals the magnetic braking force.
Takeaway: ε = BLv; the induced current always opposes the change that causes it.
Class 12 — AC circuits: impedance and resonance
Concept: in a series R-L-C circuit driven by an AC source, the inductor and
capacitor's opposing reactances partly cancel, so total impedance
Z = √(R² + (XL−XC)²) can be tuned by
frequency — and there's one frequency where it's smallest.
- Switch to AC circuit mode.
- Set Resistance R, Inductance L and Capacitance C to fixed
values, then sweep Frequency f up from low to high.
- Watch Impedance Z — it should dip to a minimum at one particular
frequency (resonance), where Peak current I₀ and Avg. power
both hit their maximum.
- Check Phase φ at that same frequency — it should be at (or very near)
zero, meaning current and voltage are in step.
Takeaway: at resonance the inductor's and capacitor's reactances exactly
cancel, leaving only the resistance to limit the current — which is why current peaks
there.