A parallel beam of monochromatic light of wavelength 5000 o A is...

The condition for the first minima in the single slit diffraction experiment can be written as

$asin\theta = \lambda . . . \left(1\right)$

Equation (1) implies that

$sin\theta = \dfrac{\lambda}{a} = \dfrac{5000 \times {10}^{- 10}}{1 \times {10}^{- 6}} = \dfrac{1}{2}$

$⇒ \theta = 30 °$