Two narrow slits are 0.025 mm apart.When a laser shines on them,bright fringes form on a screen that is a meter away.These fringes are 3.0 cm apart.What is the separation between the second order bright fringe and the central fringe?
A)8.6 cm
B)6.0 cm
C)5.3 cm
D)2.6 cm

Question

Quizplus · Accepted Answer

The separation between fringes (d) is given by d = λD/d, where λ is the wavelength of light, D is the distance from slits to screen and d is the separation between the slits. 
Here, 
d = 0.025 mm = 2.5 × 10^-5 m
D = 1 m 
Let's find the wavelength of light using the separation between fringes: 
d = λD/d 
⇒ λ = d*d/ D = (3 × 10^-2 m)*(2.5 × 10^-5 m)/1m = 7.5 × 10^-10 m
The separation between the central fringe and the second order bright fringe is given by:
x = 2d(D/d+1), where we take n=2 for the second order. 
x = 2*(2.5 × 10^-5m) * (1/(0.025 × 10^-3) + 1) = 6.0 cm
Therefore, the separation between the second order bright fringe and the central fringe is 6.0 cm. 
Hence, the correct answer is B.

Two Narrow Slits Are 0