For examples the screen on a microwave that lets light through, but not microwaves. I am having trouble visualizing it.
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When the hole is much smaller than the wavelength, the mesh looks like a solid metallic boundary. The mesh is large in comparison to visible light so you can see the lightbulb. The mesh is small in comparison to the wavelength of the microwave so it functions as a solid metallic boundary. This is basically a faraday cage and the reason you’re protected from lightning in cars and airplanes.
The lower frequency microwaves form standing waves in the microwave oven which is essentially a cavity. Think of a standing wave as having a rope tied at one end and you shake it and see peaks and valleys. This is why the food spins. It basically allows the food to heat more evenly.
As someone else mentioned, amplitude is field strength. Wavelength is what matters for your example.
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