# In interference, when light energy superimpose with a phase difference 180°, darkness occurs.

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In interference, when light energy superimpose with a phase difference 180°, darkness occurs.

1. Two sources which can give sustained interference pattern is said to be …….

2. Does interference phenomenon violate law of conservation of energy? Justify.

3. Modify the expression for band width in terms of refractive index of medium between slit and screen.

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1. Coherent sources.

2. No. In interference, only energy is redistributed.

3. We know refractive index n = $\frac{c}{v}=\frac{λ}{λ_1}$ λ$\frac{λ}{n}$ substituting this in the expression for band width  $\Big(β =\frac{λ,D}{d}\Big)$

we get β = $\frac{λD}{nd}$.