Question

A microwave oven is a kitchen appliance. Is it safe to stand by a microwave oven when it is cooking food? Should we use microwave to cook the egg in shell? Explain very accurately and in detail, using physics.

Answer 1

1) Modern microwave ovens are perfectly safe.

They work by bombarding the food inside with electromagnetic (EM) radiation with frequencies of around 2.45 GHz. In this frequency range, the charged water molecules within the food become excited and rotate backwards and forwards in the alternating electric field part of the EM wave. This action generates heat causing the food to heat up.

Because microwaves don’t have flames or heating elements as in conventional ovens, the outside of the microwave doesn’t get hot and is safe to touch. The inside is made of metal, forming what is known as a ‘Faraday Cage’ which traps the microwaves safely, preventing them leaking out. The glass window on the door has a metal grill embedded within it. The holes in the grill are usually only a couple of millimetres across, which is much smaller than the wavelength of microwave radiation (12.2cm) trapping it in the cooking chamber, but large enough for visible light to escape so you can see inside.

There could be some health risk if your microwave starts to “leak” radiation, possibly due to parts of the case or the door wearing out. If this happens, it will also heat your food less efficiently.

If you are concerned that your microwave is leaking radiation

2)

You must break the eggs out of their shells before microwaving. Never microwave eggs in shells. If you cook an egg in shell in the microwave, it’s likely to explode. Microwaves heat so quickly that steam builds up faster than an egg can ‘exhale’ it through its pores and the steam bursts through the shell. For the same reason, when microwaving, always prick the yolk of an unbeaten egg with the tip of a knife or a wooden pick. The vent you create allows the steam to escape safely.