Light of wavelength $\lambda$ is produced by two point sources R and S and reaches a screen far away. The light intensity at point P on the screen is zero. What could 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 $\frac{1}{2}\lambda$.