Question

Choose the correct answer from the alternatives given.
The frequency of electromagnetic wave, which best suited to observe a particle of radii $3\times {10}^{-4}cm$ is of the order of:

• A. ${10}^{15}$
• B. ${10}^{16}$
• C. ${10}^{13}$
• D. ${10}^{12}$

Answer 1

Answer: (C)

${10}^{13}$

Size of particle

$=2\times (3\times {10}^{-4})=6\times {10}^{-4}cm\Rightarrow 6\times {10}^{-6}m$

To observe a particle, the wavelength of electromagnetic waves must be of the size of the particle.
Hence, frequency of the wave is given by:

$f=\frac{c}{\lambda }$

$=\frac{3\times {10}^8}{6\times {10}^{-6}}=0.5\times {10}^{14}=5\times {10}^{13}Hz$