Question

The Photograph given below is obtained by passing a LASER beam on a pain of closely spaced slits.

1. Identify this pattern.

2. In the double slit experiment using wavelength 5461 A⁰ , the fringe width measured is 0.15 mm. By keeping the same arrangement, the fringe width is measured for an unknown wavelength is 0.12 mm. Find the unknown wave length.

3. If you change the LASER light from red to blue, what will happen to the space between the pattern shown in photograph. Justify

Answer 1

1. Interference

2.  β₁ = \(\frac{λ_1D}{d},β_2=\frac{λ_2D}{d}\)  \(\frac{β_1}{β_2}=\frac{λ_1}{λ_2}\)

λ₁ = 5461 A° = 5461 × 10^-10 m
β₁ = 0.15mm = 0.15 × 10^-3m
β₂ = 0.12mm = 0.12 × 10^-3m.

∴ λ₂ = \(\frac{β_2\timesλ_1}{f_1}\)

= \(\frac{546\times10^{-10}\times0.12\times10^{-3}}{0.15\times10^{-3}}\) = 4368A⁰

4. Wave length of blue is less than that of red. Hence β decreases.