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What is interference of light waves ? State two essential conditions to observe it. In Young's double slit experiment, light of wavelength 6000 overset(*)A is used to get an interference pattern on a screen. The fringe width changes by 1.5 mm when the screen is brought towards the double slit by 50 cm. Find the distance between the two slits. |
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Answer» Solution :Interference of LIGHT is the phenomenon of redistribution of light energy in medium on account of superposition of light waves from two coherent SOURCES. Conditions (i) Two sources must be coherent, so that the sources emit continuous wave of same wavelength and having no phase or constant phase difference. (ii) Two sources must be very CLOSE to each other, because the fringe width is inversely proportional to distance between the sources. In first case. `beta=(lambda D)/(d)` ...(i) In second case. `(beta-0.0015)=(lambda)/(d)(D-0.5)` ...(ii) Dividing Eq. (ii) by (i), we get `(beta-0.0015)/(beta)=(D-0.5)/(D)` `1-(0.0015)/(beta)=1-(0.5)/(D)` `(0.0015)/(beta)=(0.5)/(D)` `(D)/(beta)=(0.5)/(0.0015)=(5000)/(15)=(1000)/(3)` Now `beta=(lambda D)/(d)` or `d=lambda(D)/(beta)` or `d=6000 xx 10^(-10)((1000)/(3))` or `d=2 xx 10^(-4) m` or d =0.2 mm |
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