KCET · Physics · Communication System
An antenna uses electromagnetic waves of frequency \( 5 \mathrm{MHz} \). For proper working, the size of
the antenna should be :
- A \( 15 \mathrm{~km} \)
- B \( 15 \mathrm{~m} \)
- C \( 3 \mathrm{~km} \)
- D \( 300 \mathrm{~m} \)
Answer & Solution
Correct Answer
(B) \( 15 \mathrm{~m} \)
Step-by-step Solution
Detailed explanation
(B)
\( C=\mathrm{f\lambda} \)
\( \lambda=\frac{C}{f}=\frac{3 \times 10^{8}}{5 \times 10^{6}}=\frac{3}{5} \times 10^{2}=60 \mathrm{~m} \)
The antenna length should be \( \frac{\lambda}{4}=\frac{60}{4}=15 \mathrm{~m} \)
\( C=\mathrm{f\lambda} \)
\( \lambda=\frac{C}{f}=\frac{3 \times 10^{8}}{5 \times 10^{6}}=\frac{3}{5} \times 10^{2}=60 \mathrm{~m} \)
The antenna length should be \( \frac{\lambda}{4}=\frac{60}{4}=15 \mathrm{~m} \)
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