The diffraction pattern of a light of wavelength \( 400 \, \text{nm} \) diffracting from a slit of width \( 0.2 \, \text{mm} \) is focused on the focal plane of a convex lens of focal length \( 100 \, \text{cm} \). The width of the \( 1^{\text{st}} \) secondary maxima will be:
