A microwave oven operates predominantly at a wavelength of 12cm. The metal‐mesh viewing window in the oven door contains circular holes of diameter 2.0mm arranged in a regular grid. The user can clearly watch food heating while remaining shielded from microwave radiation.
(a) Calculate the ratio of the hole diameter to the microwave wavelength.
(b) Using your calculation and qualitative reasoning about diffraction, predict whether an appreciable fraction of microwave energy escapes through the holes. Provide an explanation.
(c) Explain why visible light from inside the oven is able to pass through the same holes even though the microwave energy is largely blocked.