Q: The frequency of EM wave which is best suited to observe a particle of radius 3 × 10^{-4} cm is of the order

(a) 10^{15}

(b) 10^{14}

(c) 10^{13}

(d) 10^{12}

Sol: If λ be the radius of the particle then λ = 3 × 10^{-6} m

Frequency of EM wave , $\large \nu = \frac{c}{\lambda} $

$\large \nu = \frac{3 \times 10^8}{3 \times 10^{-6}} = 10^{14} $

Thus to observe the particle , the frequency of wave should be more than 10^{14} Hz i.e. 10^{15} Hz or smaller value of wavelength .