Posted by **Angel** on Tuesday, April 10, 2012 at 5:49pm.

Light falls on a double slit with slit separation

of 2.19 × 10

−6 m, and the ﬁrst bright fringe is

seen at an angle of 12.7

◦

relative to the central

maximum.

What is the wavelength of the light?

Answer in units of nm

- Physics -
**Elena**, Tuesday, April 10, 2012 at 6:00pm
λ = d• tanα = 2.19•10^-6 • 0.225 =4.94 •10^-7 m = 494 nm

- Physics -
**Angel**, Tuesday, April 10, 2012 at 6:03pm
It says incorrect. Can you explain the process?

- Physics -
**Elena**, Tuesday, April 10, 2012 at 6:32pm
The coordinate of the k-maximum (separation between the central and the first maxima) is

x(max) = k•λ•L/d,

where L is the separation between the slits and the screen, d is the separation between the slits.

Now, imagine the triangle : the midpoint between slits (taking into account that the slits are very close to each other, this point is the slit), the central maximum on the screen, and the first bright fringe. In this triangle

tan α = x(1max)/L

x(1max) = L •tan α

Then for k=1

x(1max) = λ•L/d,

L •tan α =λ•L/d,

tan α = λ/d,

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