In Young's double slit experiment, fringe width is 1.4 mm with light of wavelength $6000 $$\mathop {\rm{A}}\limits^{\rm{o}} $. If the light of wavelength $5400 $$\mathop {\rm{A}}\limits^{\rm{o}} $ is used, with no other change in the experimental set up. The change in fringe width is

In a single slit diffraction experiment, slit of width ' a ' and incident light of wavelength $5600 $$\mathop {\rm{A}}\limits^{\rm{o}} $, the first minimum is observed at angle $30^{\circ}$. The first secondary maximum is observed at angle $\left(\operatorname{Sin} 30^{\circ}=0.5\right)$

In biprism experiment the maximum intensity is ' $\mathrm{I}_0$ '. If the path difference between the two interfering waves is ' $\lambda / 4$ ' then intensity at the point on the screen is

$$ \left[\sin 45^{\circ}=\cos 45^{\circ}=\frac{1}{\sqrt{2}}\right] $$

In a biprism experiment, fifth dark fringe is obtained at a point. A thin transparent film of refractive index ' $\mu$ ' is placed in one of the interfering paths. Now $7^{\text {th }}$ bright fringe is obtained at the same point. If ' $\lambda$ ' is the wavelength of light used, the thickness of film is equal to