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Physics Question 11 – NEET-UG 2024

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If the monochromatic source in Young's double slit experiment is replaced by white light, then

White light is a combination of different colors, each with a different wavelength.

Step 1: Understand the effect of white light in YDSE✦ Active

White light is polychromatic, meaning it consists of a spectrum of wavelengths (colors). In Young's Double Slit Experiment (YDSE), the interference pattern's characteristics, such as fringe position and width, depend on the wavelength of light.

Step 2: Analyze the central fringe○ Expand

At the center of the screen, the path difference between the waves from the two slits is zero for all wavelengths. This means that all colors interfere constructively at this point. Therefore, the central fringe will be bright and white.

💡 Teacher's Secret Hint

The condition for constructive interference is dsin⁡θ=nλ. For the central maximum, n=0, so dsin⁡θ=0, which is independent of λ.

Step 3: Analyze the non-central fringes○ Expand

For any other bright fringe (non-central maxima), the position (yn=nλDd) and fringe width (β=λDd) depend on the wavelength λ. Since white light contains different wavelengths, each color will form its own interference pattern. This results in colored fringes on either side of the central white fringe. Violet light (shortest wavelength) will form fringes closer to the center, while red light (longest wavelength) will form fringes farther away for a given order. The pattern becomes less distinct further from the center due to the overlapping of different colored fringes.

💡 Teacher's Secret Hint

Remember that dark fringes are formed by destructive interference, which also depends on wavelength. A perfectly dark fringe (absence of all colors) is difficult to achieve away from the central region with white light.

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