Topic 7 of 8 · Form 6
Electric and magnetic fields, induction and alternating currents
Coulomb's law F = Qq/(4πε₀r²); field strength E = F/q; uniform fields E = V/d; electric potential V = Q/(4πε₀r); motion of charged particles in uniform fields.
Notes for this topic 1 file, in order
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Electric fields
Coulomb's law F = Qq/(4πε₀r²); field strength E = F/q; uniform fields E = V/d; electric potential V = Q/(4πε₀r); motion of charged particles in uniform fields.
Capacitance
C = Q/V; energy W = ½QV = ½CV²; capacitors in series and parallel; discharge Q = Q₀e^(−t/RC); time constant τ = RC.
Worked example: A 2 200 µF capacitor charged to 12 V discharges through 5.0 kΩ. Find the time constant and the p.d. after 22 s.
τ = 11 s → V = 12e⁻² = 1.62 V
Magnetic fields
F = BIL sin θ; F = Bqv sin θ; circular paths r = mv/(Bq); Hall effect V_H = BI/(ntq); velocity selection.
Electromagnetic induction
Flux Φ = BA; flux linkage NΦ; Faraday's and Lenz's laws.
Alternating currents
I = I₀ sin ωt; rms values Irms = I₀/√2; mean power = ½I₀V₀; rectification and smoothing with a capacitor.
Check yourself
- Find the energy stored in a 470 µF capacitor at 9.0 V.
- A proton moves at 2.0 × 10⁶ m s⁻¹ perpendicular to a 0.10 T field. Find the radius (m = 1.67 × 10⁻²⁷ kg).
- The peak voltage is 325 V. Find the rms voltage.
Show answers
- 0.019 J
- 0.21 m
- 230 V
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