Question: Q. 7. Find the wavelength of electromagnetic waves of frequency $5 \times 10^{19} \mathrm{~Hz}$ in free space. Give its two applications.
A [O.D. I, II, III 2014]
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Solution:
Ans. $\quad \lambda=\frac{c}{v}=\frac{3 \times 10^{8}}{5 \times 10^{19}}=6 \times 10^{-12} \mathrm{~m}=0.06 \AA 1$
This wavelength corresponds to $X$-rays which are used :
(i) as a diagnostic tool,
(ii) as a treatment for certain forms of cancer.
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[CBSE Marking Scheme 2014]
[AT]. 8. Distinguish between any two types of propagation of electromagnetic waves based on (i) frequency range over which they are applicable and (ii) communication systems in which they are used.
U] [CBSE SQP, 2015-2016]
Ans. (i) $X$-rays and Gamma Rays : $5 \times 10^{19} \mathrm{~Hz}$
Infrared Rays : $3 \times 10^{13} \mathrm{~Hz}$
(ii) Microwaves : Aircraft navigation
Radiowaves : Radio and Television Communication system.
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