A microwave oven heats food with microwaves of frequency 2.5 GHz. The wavelength of these microwaves in vacuum is (Take \(c=3\times10^{8}\ \mathrm{m\,s^{-1}}\))
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → 12 cm
Microwaves are electromagnetic waves. So their wavelength in vacuum follows from \( \nu\lambda=c \).
\( \nu=2.5\times10^{9}\ \mathrm{Hz} \)
\( \begin{aligned} \lambda &= \frac{c}{\nu} \\ &= \frac{3\times10^{8}}{2.5\times10^{9}} \\ &= 0.12\ \mathrm{m} \\ &= 12\ \mathrm{cm} \end{aligned} \)
NCERT (2026-27):
Nature of electromagnetic waves – “… This relation is often written in terms of frequency, ν (=ω/2π) and wavelength, λ (=2π/k) as”
\( \displaystyle 2\pi\nu=c\left(\frac{2\pi}{\lambda}\right) \quad \text{or} \) \( \nu\lambda=c \)\( \qquad [8.9(b)] \)