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P1e: Cooking and
Communicating
with Waves
- Cooking with Waves
- Infrared radiation does not
penetrate food very easily
- Microwaves can penetrate glass or plastic but are
reflected by shiny metal surfaces: ––special glass in a
microwave oven door reflects microwaves ––they can
cause body tissue to burn.
- Infrared radiation does not
penetrate food very easily
- Electromagnectic Spectrum
- Energy is transferred by waves: ––the
amount of energy depends on the frequency
or wavelength of the wave ––high frequency
(short wavelength) waves transfer more
energy.
- Normal ovens cook food by infrared
radiation: ––energy is absorbed by the
surface of the food ––the kinetic energy of
the surface food particles increases ––the
rest of the food is heated by conduction.
- Microwave ovens cook food
by microwave radiation:
––the water or fat
molecules in the outer
layers of food vibrate more.
- Energy is transferred by waves: ––the
amount of energy depends on the frequency
or wavelength of the wave ––high frequency
(short wavelength) waves transfer more
energy.
- Microwave Properties
- Microwaves have wavelengths between 1 mm
and 30 cm.
- Mobile phones use longer wavelengths than microwave ovens. ––Less
energy is transferred by mobile phones.
- Microwaves have wavelengths between 1 mm
and 30 cm.
- Microwave Communication
- Microwave radiation is used to communicate
over long distances
- The transmitter and receiver must be in line of
sight. ––Aerials are normally situated on the top
of high buildings.
- Satellites are used for microwave communication. ––The signal from
Earth is received, amplified and re-transmitted back to Earth.
––Satellites are in line of sight because there are no obstructions in
space. ––Large aerials can handle thousands of phone calls and
television channels at once.
- There are concerns about the use of mobile phones and
where phone masts are situated.
- Scientists publish results of their studies to allow others to check their
findings.
- Signal strength for mobile phones can change a lot over a short distance.
––Microwaves do not show much diffraction. ––Adverse weather and large
areas of water can scatter the signals. ––The curvature of the Earth limits the
line of sight so transmitters have to be on tall buildings or close together.
- Mobile phones can interfere with
sensitive equipment: ––They are
banned on planes and in many
hospitals.
- Microwave radiation is used to communicate
over long distances
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