Solved: PHYSICS Question for NEET

NEET PHYSICSMedium

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.

Statement I is False but Statement II is True.

Both Statement I and Statement II are True.

Both Statement I and Statement II are False.

Statement I is True but Statement II is False.

Step-by-Step Solution

Analyze Statement I: The angular separation of fringes ( $\theta$ ) 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 $\theta = \frac{\lambda}{d}$ , 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 $\theta = \frac{\beta}{D} = \frac{\lambda}{d}$ . 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.
Analyze Statement II: The formula for angular separation is $\theta = \frac{\lambda}{d}$ . This shows that $\theta$ is directly proportional to the wavelength $\lambda$ ( $\theta \propto \lambda$ ). 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.
Conclusion: Statement I is correct, and Statement II is incorrect.

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