Sound waves with wavelength $\lambda$ are produced by a loudspeaker and travel through two slits $P$ and $Q$. Two sound waves from these slits arrive together at $R$. What condition must be met for a microphone at $R$ to detect an intensity maximum (loud sound)?
- AThe amplitudes of the two waves at $R$ must be the same.
- BThe distance $PQ$ must be smaller than the wavelength $\lambda$.
- CThe two waves from the slits must have travelled the same distance to $R$.
- DThe two waves must be in phase at $R$.