Class 12 Physics Electromagnetic Waves Micro Waves

Micro Waves

• Micro waves are short wavelength radio waves.
• They are produced by special vacuum tubes(klystrons/magnetrons/Gunn diodes).
• They are used in microwave ovens,and radar system in aircraft navigation.
• Air traffic control:-
• For example: - To manage air traffic. The pilot should know any other aeroplane is present nearby or not.
• The pilot should know the climatic conditions during take-off and landing.
• Speed detection
• The instrumentswhich are used to detect the speedof the vehicles which move on the roads uses radar technology.
• Military purposes
• It helps to detect enemies and weapons.
• Satellite tracking
• In order to track satellites, radar technology is used.

Why Radio waves use micro waves:-

• As they use short wavelength waves which are same as micro waves.
• They are invisible to humans. If we are able to see the waves which get transmitted it will be very irritating.
• Even the smallest presence of microwaves is easy to detect.

It consists of:-

1. Transmitter: - It transmits the microwaves.
1. Receiver: - It receives the echo produced by the microwaves when they strike any object. When the receiver receives the reflected ray then it is possible to track the presence of other object in the vicinity.

Microwave ovens

• The following are the properties because of which microwaves are very useful :-
• They have smaller wavelength.
• They get absorbed by water,fats and sugar.

Working of microwave oven:-

• In order to heat anything uniformly microwave ovens are used.
• Any food material will have water, sugar and fats in it.
• When we heat any food material inside the microwave, the microwaves penetrate inside the food.
• So the microwaves get absorbed by the water and the fat molecules.
• The molecules of the food material will start moving randomlywith some frequency.
• This is same as providing some wave to the food material with the same frequency with which the molecules start vibrating.
• This shows that the frequency of microwave matches with the frequency of the molecules.
• As all the molecules are set in random motion, temperature increases and food material gets heated uniformly throughout.
• Object can be heated by 2 ways:-
1. Conduction of heat: - It happens when anything is heated over gas burner.
2. Exciting the molecules: - This technique is used in microwave oven.

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