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JEE Main 202127 AugustEvening Shift

Exam: JEE Main
Year: 2021
Date: 27 August
Shift: Evening Shift
Subject: Physics
Chapter: Communication System

JEE Main 2021 · 27 August · Evening Shift · Physics · Communication System

An antenna is mounted on a 400m tall building. What will be the...

An antenna is mounted on a

400m

tall building. What will be the wavelength of signal that can be radiated effectively by the transmission tower upto a range of

44km

?

Options

A $605m$
B $302m$
C $37 . 8m$
D $75 . 6m$

Correct answer

A. $605m$

Step-by-step solution

d = \sqrt{2R{h}_{T}}

$⇒ 44 \times {10}^{3} = \sqrt{2 \times 6400 \times {10}^{3} \times {h}_{T}}$

$⇒ {h}_{T} = 151 . 25m$

$∵$ ${l}_{antenna} \ge \dfrac{\lambda}{4}$

$⇒ \lambda \le 4l$

considering, ${h}_{T} = 1 =$ length of antenna

$\lambda = 4 \times 151 . 25 = 605m$

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