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Physics · PYQ NEET UG 2018
हिन्दीIn Young's double slit experiment the separation \( d \) between the slits is \( 2\text{ mm} \), the wavelength \( \lambda \) of the light used is \( 5896\text{ \AA} \) and distance \( D \) between the screen and slits is \( 100\text{ cm} \). It is found that the angular width of the fringes is \( 0.20^\circ \). To increase the fringe angular width to \( 0.21^\circ \) (with same \( \lambda \) and \( D \)) the separation between the slits needs to be changed to
Correct answer · Option 2
1.9 mm
Explanation
Angular fringe width \( \theta = \frac{\lambda}{d} \). Since \( \theta d = \text{constant} \), we have \( \theta_1 d_1 = \theta_2 d_2 \). Thus \( 0.20^\circ \times 2\text{ mm} = 0.21^\circ \times d_2 \), giving \( d_2 = \frac{0.40}{0.21}\text{ mm} \approx 1.9\text{ mm} \).
