Q146 / 200 · Manipal (MET) 2011 · Physics
Two slits 4 mm apart, are illuminated by light of wavelength $6000 Å$. What will be the fringe width on a screen placed 2 m from the slits?
- A0.12 mm
- Correct answerB0.3 mm
- C3.0 mm
- D4.0 mm
Solution
Separation of slits $d=4 \mathrm{~mm}=4 \times 10^{-3} \mathrm{~m}$
Wavelength
$\lambda=6000 Å=6 \times 10^{-7} \mathrm{~m}$
Distance of screen $D=2 \mathrm{~m}$ Fringe width $\beta=\frac{\lambda D}{d}$ $\begin{aligned} & =\frac{6 \times 10^{-7} \times 2}{4 \times 10^{-3}} \\ & =3 \times 10^{-4} \mathrm{~m} \\ & =0.3 \mathrm{~mm}\end{aligned}$
Distance of screen $D=2 \mathrm{~m}$ Fringe width $\beta=\frac{\lambda D}{d}$ $\begin{aligned} & =\frac{6 \times 10^{-7} \times 2}{4 \times 10^{-3}} \\ & =3 \times 10^{-4} \mathrm{~m} \\ & =0.3 \mathrm{~mm}\end{aligned}$
Hence, the correct answer is option: 'B'.