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Lecture 5

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McGill University
ENVR 540
Christa Scholtz

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 independently. 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 health. 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. Microwave Oven Safety Standards: Before you buy a microwave, look at the label. Every microwave has a label at the back, to say that microwave is according to microwave oven safety standard. This standard was implemented in 1972. Most of our microwaves are made in 3 world rd companies, by American companies. This standard was made in US. Leaking can not be more than: 5 milliwatts of microwave radiation per square centimetre at approximately 2 inches from the oven surface. That radiation will significantly decrease with the distance (more away from the microwave, you will be safer). Today there is no danger from the microwaves, all microwaves follow this standard. What the worry is the later use of this microwave. Never use microwave that is damaged, door can close properly. While it’s operating, a microwave releases radiation. When you open the door, microwave stops to release radiation. Microwave Ovens and Human Health In theory, we don’t see any harmful effects of microwave radiation. In such a low concentration, there is no evidence that it is harmful. But, microwave radiation, in general (no just from microwave oven, but in general from anywhere), can cause some health affects. It can heat our tissue in the same way it heats food. What happens when some part of our body is overheated? Coagulation of proteins (cooking our own body) and other things. Genet
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