Question: Assertion (A) : Out of Infrared and radio waves, the radio waves show more diffraction effect. Reason (R) : Radio waves have greater frequency than infrared waves.
Step 1 (Governing Law & Given Data): [0.25 Mark]
The diffraction of a wave is inversely proportional to its frequency ($f$) and directly proportional to its wavelength ($\lambda$). The relationship between speed ($c$), frequency ($f$), and wavelength ($\lambda$) is given by:
$$c = f \lambda \implies \lambda = \frac{c}{f}$$Diffraction is significant when the size of the obstacle/aperture is comparable to the wavelength ($\lambda$) of the wave.
Step 2 (Step-by-Step Logical Working): [0.5 Mark]
- Comparing the electromagnetic spectrum: Radio waves have a much lower frequency ($f_{radio} < f_{IR}$) compared to Infrared waves.
- Using the relation $\lambda \propto \frac{1}{f}$, since $f_{radio} < f_{IR}$, it follows that $\lambda_{radio} > \lambda_{IR}$.
- Because diffraction effects are more pronounced for waves with longer wavelengths, radio waves exhibit a greater diffraction effect than infrared waves.
- Evaluating the Reason (R): The statement "Radio waves have greater frequency than infrared waves" is false, as radio waves have lower frequencies.
Step 3 (Final Concluded Answer): [0.25 Mark]
Assertion (A) is True, but Reason (R) is False.
💡 EL10 Concept Insight: Think of diffraction like a wave trying to bend around an obstacle; long, lazy waves (like radio waves) bend around corners easily, while short, fast waves (like infrared) are too "stiff" to bend and get blocked more easily.