The microwave oven was invented after a serendipitous incident when Percy Spencer accidentally melted chocolate in his pocket.
Percy Spencer worked at Ratheon, developing radar transmitters during World War II. These radar transmitters sent out microwave signals from a magnetron tube for detecting objects. One day in 1945, he accidentally discovered that the candy in his pocket was getting heated up and melting while standing next to the powered on magnetron.
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Working on this principle, he went on to invent the first working microwave oven in 1947. he called it Radarange.The first thing he cooked in it was popcorn.
But why does the microwave have a rotating glass bowl ?
It is quite entertaining to watch the rotating food in a microwave, but this rotation serves a purpose. The magnetron in a microwave oven can send the at the food, but it does not go uniformly all around. There are hot spots and cold spots within the microwave. To ensure that the food is evenly heated, it has to move around to expose all parts of the food to the microwaves equally.
Is it dangerous to open the microwave door while it is still on ?
The microwave's magnetron is supposed to switch off when you open the door. But that is just a failsafe safety mechanism. It is always better to press the stop button on the microwave BEFORE the door open button. If you have a faulty microwave, then you will be exposed to microwave radiation(though all microwave ovens in use now have safety mechanisms).
So, although it is not recommendable, it is not a real danger to open it any time. You may open the microwave door whenever you please,. Microwaves takes less than a tenth of a second to die down, and the moment you open the door a kill switch is activated for the magnetron.
Another interesting trivia is that Australian radio astronomers where confused for quite a while by strange microwave radiations picked up by their super-sensitive radio telescopes. They couldn't figure out if they were from space or interference. They called them Perytons. Later they discovered that they were caused by some old microwave ovens being opened by the door open switch before the timer was done.
A video explaining how microwave ovens work by the Engineer guy.
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