Wave Properties in Vacuum

Steps:

• Recall the wave equation for electromagnetic waves in vacuum: speed of light $c = f \lambda$, where $f$ is frequency and $\lambda$ is wavelength.
• Since $c$ is constant, rearrange to $f = \frac{c}{\lambda}$, showing inverse proportionality.
• Intensity $I$ relates to amplitude $A$ by $I \propto A^2$.
• Velocity $c$ is fixed and independent of amplitude or wavelength.

Why A is correct:

• From $c = f \lambda$, frequency $f$ is inversely proportional to wavelength $\lambda$ as $f \propto \frac{1}{\lambda}$.

Why the others are wrong:

• B: Amplitude does not affect wave velocity, which is constant at $c$.
• C: Intensity is proportional to the square of amplitude, not amplitude directly.
• D: Velocity is constant in vacuum, not varying with wavelength.

Final answer: A