Bukhovtsev-et-al-Problems-in-Elementary-Physics

434
ANSWERS AND SOLUTIONS
cent slits Is
6=BD-AC=dsln tp-dsln a
These waves add up and Intensify each other when
d (sin cp-sin 8)=kl
where k= I, 2, 3, ... for the maxima lying at the right of the central one
(Jl=O) and k=~I, -2, -3, ••• for those lying at its left.
The maximum order of the spectrum will be observed when q>=-9()O.
Thus d (-1- ~ ) =kA. Hence, k=-6. The spectrum of the sixth order
may be observed. The minus sign shows that the spectrum lies to the left
of the central one.
802. As follows from the formula d (sin q>-sin 8)=kA (see the solution
to Problem 801), the period of the grating will be minimum with tangential
Incidence of the rays: 9=90°. In this case d d ~ . Therefore, the period of
the grating should satisfy the inequality d~ ~ •
803. In the general case, as shown in the solution of Problem 801, the
sought condition will be
d (sin cp-sin 9)=kA
It may be rewritten as
2dcos CPt 9 sin cP 2 9=kA
q>+9 T 9