Alternating current

Equipment

• «Mô hình vật lý» 3D canvas: a coil rotating in a magnetic field; drag to rotate the view
• «Quan hệ định lượng» canvas: the i(t) plot updated by the parameters
• «Cảm ứng từ / mức» (magnetic field / level) slider, 0.10–1.00 T
• «Góc / tốc độ» (angle / speed) slider, factor 0.33–2.22×
• «Tạm dừng / Chạy tiếp» (pause/resume) buttons per panel; readout «i(t)=I₀ sin(ωt), T=2π/ω; I hiệu dụng = I₀/√2 = …»

Procedure

1. Change the amplitude via the magnetic field

   In «1. Mô hình vật lý», slide «Cảm ứng từ / mức» from 0.10 to 1.00 T and watch the coil and the plot: the amplitude I₀ is proportional to B because the induced emf follows the flux. Read «I hiệu dụng = I₀/√2 = …» at two B values and check that the RMS ratio matches the B ratio; compare with $I_{rms} = I_0/\sqrt{2}$.

2. Change the angular frequency

   Raise «Góc / tốc độ»: the coil spins faster and the «2. Quan hệ định lượng» plot packs more cycles into the same time — ω increases so $T = 2\pi/\omega$ shrinks. Count the cycles on the graph at two speed settings and compare the ratio with the displayed factor (e.g. ×2.00 vs ×1.00 should double the cycles).

3. Freeze the graph and read the phase

   Press «Tạm dừng» under the graph to freeze i(t). Read i at the marked instant and check it against $i = I_0\sin(\omega t)$: when the coil plane is parallel to the field the flux is zero but its rate of change is maximal, so i peaks. Press «Chạy tiếp» to let the point move on.

4. Predict and cross-check

   Predict first: does doubling «Góc / tốc độ» change the amplitude, or only the frequency? Since the peak emf $\mathcal{E}_0 = N B S \omega$, spinning faster raises both frequency and amplitude. Check on the RMS readout while changing speed with B fixed; then tabulate I₀(B) at fixed speed to confirm the linear relation.

Simulation

Experiment history

Related physicists

Related library topics