Why, for Young’s double slit experiment, does the wavelength have to be greater than or equal to the slit?

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<h2 class="title">Diffraction Through a Single Slit</h2>
<p>Waves diffract when they encounter obstacles. Why does this happen? If we apply Huygens principle it becomes clear. Think about a wavefront impinging on a barrier with a slit in it, only the points on the wavefront that move into the slit can continue emitting forward moving waves - but because a lot of the wavefront has been blocked by the barrier, the points on the edges of the hole emit waves that bend round the edges. How to use this approach to understand what happens is sketched below:</p>
<img alt="751aa8f2c0ba37b29db999e9394b23ad.png" src="https://data.ulearngo.com/assets/83e367b1-ffb4-49ae-b5b9-3ef485ad74a4"/>
<p>Before the the wavefront strikes the barrier the wavefront generates another forward moving wavefront (applying Huygens' principle). Once the barrier blocks most of the wavefront you can see that the forward moving wavefront bends around the slit because the secondary waves they would need to interfere with to create a straight wavefront have been blocked by the barrier.</p>
<p>If you employ Huygens' principle you can see the effect is that the wavefronts are no longer straight lines.</p>
<img alt="ba842f1d0f8b23fa0daf816d6e31873c.png" src="https://data.ulearngo.com/assets/f5c9621b-f3cc-49a2-826d-b7b837b7e1c2"/></section>
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Diffraction Through a Single Slit

Physics is a science discipline concerned with the nature and properties of matter and energy. Physics topics include mechanics, heat, light and radiation, sound, electricity, magnetism, the structure of atoms, and so on.

Physics

Explore the properties and behaviors of electromagnetic waves, including their wave-like and particle-like nature, EM fields, penetrating abilities, diffraction, and the Doppler effect, and gain an understanding of the electromagnetic spectrum, animal behavior, 2D and 3D wavefronts, Huygen&#8217;s principle, and the expanding universe.


Diffraction Through a Single Slit

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