Section 6.1 · Problems · 7 of 11
Problem 6.1.7: Induced current in a small wire loop
Induced current in a small wire loop
#A uniform plane time-harmonic electromagnetic wave propagates in free space carrying a time-average power of per unit area of the wavefront, at a frequency of . A circular wire loop of radius is positioned in the field of the wave such that the rms emf induced in it is maximum. The inductance and resistance of the loop are and , respectively. Compute the rms intensity of the current induced in the loop, neglecting the magnetic field it produces (use the impedance of the loop).
Source: B. M. Notaroš, Electromagnetics, Problem 9.11.
Follow the chain flux emf current. The loop is small (), so is uniform over it, and it behaves as a series – circuit driven by the induced emf of Faraday's law (Section 5.3).
In free space :
and the rms value is .
The flux is , being the angle between and the normal of the loop. The emf is largest for : the loop lies in the plane of and , as in the figure. Faraday's law in phasor form, , gives
, , and
Since , with , and . The current lags the emf by and dissipates only .
Mind the denominator: it is . Writing instead is a common slip. The result, , uses the correct form.