Question

Two slits $4\, mm$ apart, are illuminated by light of wavelength $6000\, ?$. What will be the fringe width on a screen placed $2\, m$ from the slits?

• A. 0.12 mm
• B. 0.3 mm
• C. 3.0 mm
• D. 4.0 mm

Answer 1

Answer: (B)

0.3 mm

Answer 2

Separation of slits $d=4\, mm =4 \times 10^{-3} m$ Wavelength $\lambda=6000\, ?=6 \times 10^{-7} m$ Distance of screen $D=2\, m$ Fringe width $\beta =\frac{\lambda D}{d}$ $=\frac{6 \times 10^{-7} \times 2}{4 \times 10^{-3}}$ $=3 \times 10^{-4} m$ $=0.3\, mm$