Fundamentals of Electricity and Magnetism
What this domain tests
Fundamentals of Electricity and Magnetism tests Ohm’s law, series and parallel circuits, AC RMS and power, magnetic flux, and electromagnetic induction. Answers must be unit-correct and show the formula used.
Core rules
- Ohm’s law: V = IR. Power: P = VI = I²R = V²/R.
- Series: same current, voltages add, R_total = R1 + R2. Parallel: same voltage, currents add, 1/R_total = 1/R1 + 1/R2.
- For a sine wave, RMS = peak/√2; a 230 V supply is 230 V RMS, about 325 V peak. Form factor = 1.11.
- Magnetic flux Φ is in webers; flux density B = Φ/A in tesla; mmf = NI. Faraday’s law e = N dΦ/dt; Lenz’s law opposes the change.
Worked example
A 230 V, 2 kW heater is connected to a stable supply. I = P/V = 2000/230 = 8.70 A. Its resistance is R = V/I = 230/8.70 = 26.4 Ω. Check: P = V²/R = 230²/26.4 ≈ 2004 W. If the supply falls to 200 V and resistance stays constant, P = 200²/26.4 ≈ 1515 W, so heat output drops.
Traps that cost marks
Using peak voltage in power calculations, mixing W and kW, adding parallel resistances directly, ignoring power factor in AC loads, and forgetting that induced emf opposes the flux change. In magnetic circuits, an air gap has high reluctance and reduces flux for the same mmf.