Which of the EM waves with following wavelengths is relatively harmful for human body?
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → \( 30\,\mathrm{nm} \)
The harm a radiation does depends on its photon energy, which increases as the wavelength decreases (\( E = hc/\lambda \)).
2000 nm and 1000 nm lie in the infrared, and 700 nm is at the red end of the visible range; these photons carry about 0.6 eV to 1.8 eV, mostly producing only heating.
30 nm lies in the ultraviolet region (far UV). Its photons carry about
\( \displaystyle E = \frac{1240}{\lambda\,(\mathrm{nm})}\,\mathrm{eV} = \frac{1240}{30}\,\mathrm{eV} \approx 41\,\mathrm{eV} \)
This is enough to ionise atoms and damage living cells, so 30 nm radiation is the most harmful to the human body.
NCERT (2026-27):
Ultraviolet Rays – “It covers wavelengths ranging from about 4 × 10–7 m (400 nm) down to 6 × 10–10 m (0.6 nm). … UV light in large quantities has harmful effects on humans.”