To radiate EM signal of wavelength $\lambda$ with high efficiency, the antennas should have a minimum size equal to :

JEE Main · 2023 · 13 Apr 2023 · Shift 2 · EM Waves

To radiate EM signal of wavelength

λ

with high efficiency, the antennas should have a minimum size equal to :

(A) $\frac{λ}{2}$
(B) $\frac{λ}{4}$ ✓ Correct
(C) $2 λ$
(D) $λ$

Answer: (B)

Solution

An antenna radiates efficiently only when its physical size is comparable to the wavelength of the signal it transmits, because a very short conductor cannot sustain a standing wave of that signal. The smallest length that supports such a standing wave corresponds to one quarter of the wavelength, so the minimum antenna size is

\frac{λ}{4}

JEE Main · 2023 · 13 Apr 2023 · Shift 2 · Single correct option

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