ENVR 203 Lecture Notes - Lecture 5: Electromagnetic Spectrum, Smoke Detector, Vacuum Tube

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26 Jan 2013

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Nonionized Radiation: Radiation that has lower energy. Not enough energy to displace electrons
from the atoms. This radiation does cause harm, but that harm is not obvious. It is a subject of
debate and research. We will look at some case studies about it. It’s hard to generalize things
about nonionized radiation, because there isn’t enough evidence, but we can look at each case
Microwave Radiation: Widely used that even we don’t know of. For example, if you are driving
fast, and police stops you, microwave radiation is to blame. To send telephone and television
communications. To treat muscle sourness. To dry and cure plywood (If plywood is damaged
during processing, microwave radiation is used to find where is it damaged). To raise bread and
doughnuts (used in companies, but not much at homes). To cook potato chips. Microwave oven.
Microwave Oven Radiation: Microwave radiation is electromagnetic radiation. Radiation from
the sun is also an electromagnetic radiation. Microwave radiation is used for cooking because it
is easily absorbed by foods. As soon as this radiation enters food, it gets transferred into heat.
Plastic, glass, ceramic don’t absorb microwave radiation, and they are not heated during cooking
of food (Microwave safe plastic). Passes through glass, paper, and plastic. This radiation is
reflected by the metal. It can be absorbed into metal, and metal won’t heat up. Microwave
radiation just bounces on the metal surface, and it won’t be absorbed. This is why you don’t cook
any thing in metal in microwave oven.
What are we doing when we are cooking?
Microwave is made up of metal. Inside parts are metal. Its appliances produce microwave
radiation. Microwaves bounce back and forth within the metal interior and reach the food. When
it reaches the food, this radiation gets transferred into heat. How? Most of our foods have water
inside, and the molecule of the water vibrates, producing heat that cook the food. This food is
safe to eat, as there is not radiation in the food, but in interior of microwave there is radiation, but
food is not contaminated. One problem, food is always cooked from the outside, but not from
inside (Cooks from outside to inside). Biggest problem is that food is not always cooked evenly
(That is why microwave turns around, to make cooking more even). This creates problems to
Advantages to cooking in microwave: faster, convenient, and not messy. Most vitamins and
minerals stay in the food because cooking is faster and we don’t need to add water. For example,
in conventional cooking, we add water, and there is a belief that minerals from food will enter
the water, and we don’t drink that water. With microwave, most vitamins stay in the food
(healthier food). Problem is that plastic and glass is not heated by the microwave, but can be
heated by the food, and can get very hot. Cases show many situations of burning, NOT from
radiation but overheated food. One study showed, if you take a glass of water, and put in
microwave and cook for a very long time, that water will get extremely hot, but you won’t see
that water boiling. You will think its safe, and if you remove that cup and put, for example, a
spoonful of coffee, it will explode, because the water will be heated above the boiling point.
Using safe plastic is better for our health, because normal plastic can melt and certain chemicals
can be released in our food. Don’t use metals and aluminium foils in microwave.
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