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Exam
NEET
Subject
Physics
Chapter
Electromagnetic Waves

NEET · Physics · Electromagnetic Waves

An LC circuit is used as a transmitter to generate electromagnetic...

An LC circuit is used as a transmitter to generate electromagnetic waves in free space. If the circuit contains an inductor of inductance L=2.5π2L = \dfrac{2.5}{\pi^2} mH and a capacitor of capacitance C=1C = 1 μ\muF, what is the wavelength of the emitted electromagnetic wave?
(Take the speed of light in vacuum c=3×108c = 3 \times 10^8 m/s)

Options

  1. A1.5×104π\dfrac{1.5 \times 10^4}{\pi} m
  2. B10410^4 m
  3. C3×1043 \times 10^4 m
  4. D6×104π6 \times 10^4 \pi m

Correct answer

C. 3×1043 \times 10^4 m

Step-by-step solution

The frequency of the emitted electromagnetic wave is equal to the resonant frequency of the oscillating charge in the LC circuit.

The resonant frequency is given by:
f=12πLCf = \dfrac{1}{2\pi \sqrt{LC}}

Given L=2.5π2×10−3L = \dfrac{2.5}{\pi^2} \times 10^{-3} H and C=10−6C = 10^{-6} F, we have:
LC=2.5×10−9π2=25×10−10π2LC = \dfrac{2.5 \times 10^{-9}}{\pi^2} = \dfrac{25 \times 10^{-10}}{\pi^2}

LC=5×10−5π\sqrt{LC} = \dfrac{5 \times 10^{-5}}{\pi} s

Substituting this into the frequency formula:
f=12π(5×10−5π)=110×10−5=104f = \dfrac{1}{2\pi \left( \dfrac{5 \times 10^{-5}}{\pi} \right)} = \dfrac{1}{10 \times 10^{-5}} = 10^4 Hz

The wavelength λ\lambda of the electromagnetic wave in free space is:
λ=cf=3×108104=3×104\lambda = \dfrac{c}{f} = \dfrac{3 \times 10^8}{10^4} = 3 \times 10^4 m

Answer: 3×1043 \times 10^4 m
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