Question: The electromagnetic waves used to purify water are
Step 1 (Identification of Electromagnetic Spectrum Properties): [0.5 Mark]
According to the NCERT Physics textbook (Chapter: Electromagnetic Waves), different regions of the electromagnetic spectrum are characterized by their specific frequency ranges and applications. Ultraviolet (UV) radiation, which lies in the frequency range of approximately $8 \times 10^{14} \text{ Hz}$ to $5 \times 10^{16} \text{ Hz}$, possesses sufficient energy to damage the DNA of microorganisms.
Step 2 (Application Analysis): [0.25 Mark]
The germicidal property of electromagnetic waves is directly proportional to their photon energy, given by the relation:
$$E = h\nu = \frac{hc}{\lambda}$$Where:
- $E$ = Energy of the photon
- $h$ = Planck's constant ($6.626 \times 10^{-34} \text{ J}\cdot\text{s}$)
- $\nu$ = Frequency of the wave
- $\lambda$ = Wavelength
UV rays have a shorter wavelength and higher frequency than visible light, allowing them to penetrate the cell walls of bacteria and viruses, effectively neutralizing them without the use of chemicals.
Step 3 (Final Concluded Answer): [0.25 Mark]
Comparing the given options, Ultraviolet rays are the standard electromagnetic waves used in water purifiers for sterilization. Therefore, the correct option is (B).
💡 EL10 Concept Insight: Think of Ultraviolet rays like tiny, invisible "energy bullets" that are just the right size to break the genetic code of germs, making it impossible for them to reproduce and keep you sick!