Cooking and Communicating with Waves – Revision Pack (P1)
Cooking with Waves:
Infrared radiation does not penetrate food very easily.
Microwaves penetrate up to 1cm into food. Microwaves can penetrate plastic and
glass but are reflected by shiny metal surfaces. Special glass is used in microwave
oven doors which reflect microwaves. Microwaves can penetrate the skin.
Electromagnetic Spectrum:
Energy is transferred by waves. The amount of energy transferred is dependent on
the wavelength and frequency of the wave.
High frequency waves (which have short wavelengths) will transfer more energy.
Cooking by Infrared Radiation (in normal
cooking ovens)
STEP 1 – Energy is absorbed by the surface
of the food
STEP 2 – The kinetic (movement) energy on
the surface of the food increases
STEP 3 – The remainder of the food (the
inner layers) is cooked by conduction
Cooking by Microwave Radiation (in
microwave ovens)
STEP 1 – The water and or fat molecules on
the outer layers of the food vibrate more
STEP 2 – The kinetic energy on the upper
layers of the food increases
STEP 3 – Energy is transferred to the rest of
the food by conduction
Microwave Properties:
Microwaves have wavelengths between 1mm and 20cm – REMEMBER this!
Mobile phones use longer wavelengths than microwave ovens. Longer wavelengths
mean less energy, SO less energy is transferred by mobile phones.
Communication with Microwaves:
Microwave radiation is used to communicate over long distances.
The transmitter and the receiver need to be in line of site. This is why aerials are
normally put on top of very tall buildings.
Satellites (like the one to the left) are used
in microwave communication.
The signal from earth is received, amplified
and re-transmitted to earth.
There are no obstructions in space, so as
long as you’re not underground, it is always
in the line of site.
Aerials (which receive the re-transmitted
signals) can handle thousands of phone
calls and television programmes at once.
Cooking and Communicating with Waves – Revision Pack (P1)
There are many concerns over the use of mobile phones and where phone masts
should be situated. Many people believe that we should not allow young children to
use mobile phones, perhaps because it causes brain damage. Research into this is
NOT conclusive however. The scientists who conducted the study released their
results to allow others to check their results.
Signal strength can change over very short distances. Microwaves show little
diffraction (spreading out of signal). Adverse weather conditions and large areas of
water can scatter signals.
The curvature of the earth limits the line of site, so transmitters are often placed on
tall buildings or very close together.
NOTE – mobile phones can interfere with sensitive equipment, this is why we have to
turn our phones off on planes and when we’re in the airports.
Cooking and Communicating with Waves – Revision Pack (P1)
Past Papers:
PPQ(1):
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Mark Schemes:
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