For Young's double-slit experiment, two statements are given below:
Statement I: If screen is moved away from

Question

For Young's double-slit experiment, two statements are given below:
Statement I: If screen is moved away from the plane of slits, angular separation of the fringes remains constant.
Statement II: If the monochromatic source is replaced by another monochromatic source of larger wavelength, the angular separation of fringes decreases.

Accepted Answer

1. **Analyze Statement I:** The angular separation of fringes ($	heta$) in Young's Double Slit Experiment is defined as the angle subtended by a fringe width at the slits. It is given by the formula $	heta = \frac{\lambda}{d}$, where $\lambda$ is the wavelength of light and $d$ is the distance between the slits. Alternatively, using the linear fringe width $\beta = \frac{\lambda D}{d}$, the angular separation is $	heta = \frac{\beta}{D} = \frac{\lambda}{d}$. This expression is independent of $D$ (the distance between the slits and the screen). Therefore, moving the screen away does not change the angular separation. **Statement I is True.**
2. **Analyze Statement II:** The formula for angular separation is $	heta = \frac{\lambda}{d}$. This shows that $	heta$ is directly proportional to the wavelength $\lambda$ ($	heta \propto \lambda$). If the source is replaced by one with a *larger* wavelength, the angular separation must *increase*. The statement claims it decreases. **Statement II is False.**
3. **Conclusion:** Statement I is correct, and Statement II is incorrect.

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