GATE 2020 PH – Question 55
A plane electromagnetic wave of wavelength λ is incident on a circular conducting loop of radius $a\ll\lambda$. Find the angle in degrees between the Poynting vector and loop normal that permits maximum induced electrical signal.
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Show answer and explanation
Correct answer: -270 to -270 OR -90 to -90 OR 90 to 90 OR 270 to 270
Explanation
Faraday induction depends on magnetic flux through the loop, so the magnetic field must be aligned with the loop normal to maximize the signal. In a plane wave, the Poynting vector is perpendicular to B. It must therefore be perpendicular to the loop normal, giving 90° modulo 180°. The official key accepts −270°, −90°, 90° or 270°, all retained as separate exact alternatives. The polarization must also supply the required B orientation.