Question

In YDSE a source of wavelength 6000 Å is used. The screen is placed 1 m from the slits. Fringes formed on the screen, are observed by a student sitting close to the slits. The student's eye can distinguish two neighbouring fringes. If they subtend an angle more than 1 minute of arc. What will be the maximum distance between the slits so that the fringes are clearly visible

• A. 2.06 mm
• B. 2.06 cm
• C. 2.06 × 10^–3 mm
• D. None of these

Answer 1

Answer: (A)

2.06 mm

Answer 2

According to given problem angular fringe width

$\theta = \frac{\lambda}{d} \geq \frac{\pi}{180 \times 60}$ $\lbrack\text{As }1' = \frac{\pi}{180 \times 60}rad\rbrack$

i.e. $d < \frac{6 \times 10^{- 7} \times 180 \times 60}{\pi}$ i.e. $d < 2.06 \times 10^{- 3}m$

⇒ $d_{\max}$