Electricity & Magnetism · AP Physics 2 Unit 3
Coulomb Law & Electrostatic Induction Simulator
Key exam takeaway: Electrostatic induction rule: "Opposite near, like far". Bringing a positive rod near an electroscope induces negative charge on the top knob and like positive charge on the diverging leaves.
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3D Simulation Stage● 60 FPS
Parameter Controls
μC
μC
m
Live Derivations & Metrics
Coulomb Force F
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Force Character
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Leaf Divergence Angle
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Interior Electric Field E
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Real-Time Formula Derivation
Governing Formula:
--Substitution:
--Regime: --
Worked Examples & Exam Question Deep Dive
Worked Problem
Problem: Two charges feel force F at distance r. If both charges double and distance halves, what is the new force?
Step-by-Step Derivation:
- From F = k(q1*q2)/r²: numerator becomes 2*2=4, denominator becomes (0.5)²=0.25. New force F' = 4/0.25 * F = 16F.
Worked Problem
Problem: Airplanes are frequently struck by lightning mid-flight. Why are passengers and avionics completely unharmed?
Step-by-Step Derivation:
- Faraday cage effect. The aluminum fuselage acts as a closed conductive shield; lightning currents route harmlessly over the exterior skin.
Student Inquiry Worksheet & Practice Problems
Q1. Variant 1: What charges do fur-rubbed rubber and silk-rubbed glass acquire? What is the microscopic mechanism?
Answer Key: Rubber: negative (gains electrons). Glass: positive (loses electrons). Friction transfers existing electrons based on electron affinity.
Q2. Variant 2: Identical metal spheres with +6q and -2q contact and separate. What is final charge on each?
Answer Key: Charge conservation: net charge = (+6q) + (-2q) = +4q. Spheres share equally, leaving +2q on each.
Q3. Variant 3: What three electrostatic equilibrium conditions characterize a conductor?
Answer Key: 1) Internal electric field is strictly zero everywhere; 2) net charge resides exclusively on the outer surface; 3) conductor is an equipotential volume.
Frequently Asked Questions & Misconceptions
When r approaches zero, does Coulomb force become truly infinite?
No! Coulomb's law assumes ideal "point charges". At near-zero distances, physical size and charge redistribution invalidate the point-charge model.
In a thunderstorm car lightning strike, is it safer inside the car or running out?
Stay inside! The steel automotive body acts as a protective Faraday cage directing lightning into the ground. Exiting exposes you as a lightning rod.
Why does an electrostatic plastic comb attract electrically neutral paper bits?
Dielectric polarization! The comb's field induces dipole polarization in paper bits; closer opposite charges experience greater attraction than distant like charges.
Why does a microwave door metal mesh block microwaves while letting visible light through?
Mesh holes (1mm) are much smaller than 12.2cm microwaves, acting as a continuous Faraday shield, but much larger than 500nm light waves.