CALCULATIONS:-

i) theta = (lamda) / (2 beta)
= 5890 x 10^-8 cm / 2 x 0.0197 cm
= 1.495 x 10^-3 radians.

ii) t = l theta
= 3.256 x 1.495 x 10^-3 cms
= 4.868 x 10^-3 cms.