Question

If amplitude of waves at distance r from a point source is A, the amplitude at a distance 2r will be

• A. 2A
• B. A
• C. A/2
• D. A/4

Answer 1

Answer: (C)

A/2

Answer 2

I ∝ A² and I $\propto \frac{1}{r^{2}}$ so r$\propto \frac{1}{A}$; $\frac{r_{1}}{r_{2}} = \frac{A_{2}}{A_{1}} \Rightarrow$A₂ = A₁ $\left( \frac{r_{1}}{r_{2}} \right)$= A $\left( \frac{1}{2} \right)$= A/2