By clicking the two-slit barrier and dragging it, you can change its position. Always allow a few seconds for the simulation to catch up with the changes you are making before analyzing the results. When the two-slit barrier is brought closer to the screen (and farther away from the source), what happens to the distance between two adjacent bright (or dark) fringes?

A. It becomes larger.

B. It becomes smaller.

C. It stays the same.

the answer the correct one is B

Explanation:

The interference phenomenon is described by

           d sin θ = m λ

The spectrum is recorded on a screen, so we can use trigonometry

          tan θ = y / L

In this experiment the angles are very small, so

           tan θ = sin θ /cos θ = sin θ

  We replace

         d y / L = m La m

        y = m Lam L / d

When the slits approach the screen the value of L decreases,

Therefore the value of the separation between the slits must also decrease

When reviewing the answer the correct one is B

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