Light with wavelength $\lambda$ is produced by two point sources R and S and reaches a screen far away. At point P on the screen, the light intensity is zero. What might account for the zero intensity at P?
- ALight from the two sources is emitted $180^{\circ}$ out of phase and the path difference to P is $\frac{1}{2}\lambda$.
- BLight from the two sources is emitted in phase and the path difference to P is $\lambda$.
- CLight from the two sources is emitted $90^{\circ}$ out of phase and the path difference to P is $\lambda$.
- DLight from the two sources is emitted in phase and the path difference to P is $\frac{1}{2}\lambda$.