12. For diffraction of waves by a single slit of width a at a distance D from the screen, which is right?
(A)the first maximum occurs at \( a\sin\theta = \lambda \)
(B)smaller a will result in larger separations between minima
(C)the intensity of each maximum is the same
(D)the diffraction is more easily observed for lights of shorter wavelength than those of longer wavelength
(E)the first maximum occurs at \( a\sin\theta = 3\lambda/2 \)