Three waves of equal frequencies having amplitudes $10\ \mu\text{m}$, $4\ \mu\text{m}$ and $7\ \mu\text{m}$…

Three waves of equal frequencies having amplitudes $10\ \mu\text{m}$, $4\ \mu\text{m}$ and $7\ \mu\text{m}$ arrive at a given point with successive phase difference of $\frac{\pi}{2}$. The amplitude of the resulting wave (in $\mu\text{m}$) is given by
  1. 7
  2. 6
  3. 5
  4. 4

Solution

Using vector algebra, [The diagram shows two opposite horizontal vectors of $10\ \mu\text{m}$ and $7\ \mu\text{m}$ resolving into a net horizontal vector of $3\ \mu\text{m}$, perpendicular to a vertical vector of $4\ \mu\text{m}$.] $\Rightarrow$ Resulting wave, $A_R = \sqrt{(4)^2 + (3)^2} = 5\ \mu\text{m}$

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