They are also used in industry for processing materials, in medicine for diathermy treatment and in kitchens for cooking food. At one time there was concern that leakage from microwave ovens could interfere with certain electronic cardiac pacemakers. Organs with a poor blood supply and temperature control, such as the eye, or temperature-sensitive tissue like the testes, have a higher risk of heat damage. Food safety: Food safety is an important health issue. Microwaves are produced by the vibration of chemical bonds which produces heat which helps in heating the food. These notes will certainly save your time during stressful exam days. In addition, FDA requires that all ovens made after October 1975 have a label explaining precautions for use. Also, because metal reflects microwaves, food wrapped in metal foil will not be cooked, while food not in metal wrap may receive more energy than intended, causing uneven cooking. Microwaves are a form of electromagnetic radiation; that is, they are waves of electrical and magnetic energy moving together through space. These are produced by hot bodies and molecules. The best app for CBSE students now provides Electromagnetic Waves class 12 Notes latest chapter wise notes for quick preparation of CBSE board exams and school-based annual examinations. Domestic microwave ovens operate at a frequency of 2450 MHz with a power usually ranging from 500 to 1100 watts. An electric charge oscillating harmonically with frequency. It was incredibly hot and energetic. In a microwave oven, the rate of heating depends on the power rating of the oven and on the water content, density and amount of food being heated. Many states have programs for inspecting ovens or they may be able to refer you to microwave oven servicing organizations that are equipped to test ovens for emissions. Domestic microwave ovens operate at a frequency of 2450 MHz with a power usually ranging from 500 to 1100 watts. But the most common consumer use of microwave energy is in microwave ovens. People have been severely burned by super-heated water.Another peculiarity of microwave cooking relates to the thermal response of specific foods. Microwaves are used primarily for TV broadcasting, radar for air and sea navigational aids, and telecommunications including mobile phones. While most modern ovens can tolerate some food packaging made of metal, oven manufacturers generally recommend not placing metal in the oven, particularly not close to the walls, as this could cause electrical arcing and damage the oven walls. How are microwaves produced? Microwaves are produced by an electronic tube called a magnetron. Electromagnetic Waves class 12 Notes. In a microwave oven there may be no bubbles on the walls of the container and the water will super-heat and may suddenly boil. When used according to manufacturers' instructions, microwave ovens are safe and convenient for heating and cooking a variety of foods. Food cooked in a microwave oven is as safe, and has the same nutrient value, as food cooked in a conventional oven. The main difference between these two methods of cooking is that microwave energy penetrates deeper into the food and reduces the time for heat to be conducted throughout the food, thus reducing the overall cooking time. Exposure limits for workers and for the general public are set well below levels where any hazardous heating occurs from microwave exposure. The Food and Drug Administration (FDA) regulates the manufacture of microwave ovens. NCERT Solutions, NCERT Exemplars, Revison Notes, Free Videos, CBSE Papers, MCQ Tests & more. Infrared rays – produced by hot bodies and molecules. How to Create Worksheets using Test Generator? Boiling water on a conventional stove allows steam to escape through bubbling action as the water begins to boil. Users should check that the door closes properly and that the safety interlock devices, fitted to the door to prevent microwaves from being generated while it is open, work correctly. [Foreign 2011] ... Microwaves are produced by special vacuum tubes like klystrons, magnetrons and gunn diodes. The International Commission on Non-Ionizing Radiation Protection (ICNIRP) has published guidelines on exposure limits for the whole EMF part of the spectrum. CBSE Reduced Syllabus by 30% for Session 2020-21, When CBSE will Conduct Remaining Exams (COVID-19), CBSE Board Exams Postponed Till March 31, 2020, Faraday’s law of eletromagnetic induction-. In practice, emissions from modern domestic microwave ovens are substantially below this international limit, and have interlocks that prevent people being exposed to microwaves while the oven is on. If there is some problem and you believe your oven might be leaking excessive microwaves, contact the oven manufacturer, a microwave oven service organization, your state health department, or the nearest FDA office. This Information Sheet discusses the operation and safety aspects of microwave ovens used in the home. Your IP: Exposure limits for workers and for the general public are set well below levels where any hazardous heating occurs from microwave exposure. Even if you wish to have an overview of a chapter, quick revision notes are here to do if for you. It is used in manufacture of polyethylene from ethylene. Much research has been done with experimental animals, but it is difficult to translate the effects of microwaves on animals to possible effects on humans. Ask for details ; Follow Report by Mehul46 17.02.2018 Log in to add a comment Kelly Classic, Certified Medical Physicist. Exposure to high levels of microwaves can cause a painful burn. Where  is the permeability of the medium and  its permittivity. The emission limit for microwave ovens mentioned above is consistent with the exposure limits recommended by ICNIRP. Coronavirus disease outbreak (COVID-2019), Coronavirus disease outbreak (COVID-19) »,, PDF version: EMF & public health: Microwave ovens. Some oven manufacturers will arrange for your oven to be checked. This can lead to a health risk if parts of the food are not heated sufficiently to kill potentially dangerous micro-organisms. Another peculiarity of microwave cooking relates to the thermal response of specific foods. They are reflected by the metal sides of the oven cavity and absorbed by the food. Ultraviolet light → C)Given off by very hot objects, such as the sun Heat from warm objects The microwaves are reflected within the metal interior of the oven where they are absorbed by food. The World Health Organization (WHO), through the International EMF Project, has established a programme to review research results and conduct risk assessments of exposure to electromagnetic fields in the range from 0 to 300 GHz. When used according to manufacturers' instructions, microwave ovens are safe and convenient for heating and cooking a variety of foods. If you are on a personal connection, like at home, you can run an anti-virus scan on your device to make sure it is not infected with malware. An electric dipole is a basic source of electromagnetic waves. Once the oven is switched on, the microwaves are dispersed in the oven cavity and reflected by a stirrer fan so the microwaves are propagated in all directions. This can happen if eggs or chestnuts are cooked in their shells.Food safety: Food safety is an important health issue. If total energy transferred to a surface in time. Uniformity of heating in the food is usually assisted by having the food on a rotating turntable in the oven. Write in brief, how these waves can be produced. These are the Electromagnetic Waves class 12 Notes prepared by team of expert teachers. Several countries, as well as the International Electrotechnical Commission (IEC), the International Committee on Electromagnetic Safety (ICES) of the Institute of Electrical and Electronics Engineers (IEEE) and the European Committee for Electrotechnical Standardization (CENELEC), have set a product emission limit of 50 watts per square metre (W/m2) at any point 5 cm away from the external surfaces of the oven. There is no residual radiation remaining after microwave production has stopped. Furthermore, as you move away from an oven, the level of any leaking microwave radiation that might be reaching you decreases dramatically. Unlike conventional ovens, microwaves are absorbed only in the food and not in the surrounding oven cavity. Class 12 Physics notes on chapter 8 Electromagnetic Waves are also available for download in CBSE Guide website. More details about the nature of electromagnetic fields and health effects of radiofrequency and microwave fields are available in WHO Fact Sheets 182 and 183. However, thermal damage would only occur from long exposures to very high power levels, well in excess of those measured around microwave ovens.Thermal safety: Burn injuries can result from handling hot items heated in a microwave oven, in the same way as items heated using conventional ovens or cooking surfaces. To make sure the standard is met, FDA tests microwave ovens. Microwaves do not directly heat food containers which are designed for microwave cooking. Although heat is produced directly in the food, microwave ovens do not cook food from the "inside out." Microwaves are produced inside the oven by an electron tube called a magnetron. Microwave oven users should carefully read and comply with the manufacturer’s instructions because new ovens vary widely in design and performance. All microwave ovens made after October 1971 are covered by a safety standard enforced by the FDA. Because of the potential for uneven distribution of cooking, food heated in a microwave oven should rest for several minutes after cooking is completed to allow the heat to distribute throughout the food. Certain items with non-porous surfaces (e.g. For example, someone standing 20 inches from an oven would receive approximately one one-hundredth of the amount of microwaves received at 2 inches. (Delhi 2014) Answer: (a) Microwaves Production : Klystron/magnetron (b) Infrared Radiations Production ; Hot bodies/vibrations of atoms and molecules. Microwaves are reflected, transmitted or absorbed by materials in their path, in a similar manner to light. It is known that microwave radiation can heat body tissue the same way it heats food. Microwave ovens use them for cooking. For one thing, there are differences in the way animals and humans absorb microwaves. These product emission limits are defined for the purpose of compliance testing, not specifically exposure protection. Today, the universe is 93 billion light-years wide, and the CMB represents a temperature of about 2.7 Kelvin. They are reflected by the metal sides of the oven cavity and absorbed by the food. This is far below the level known to harm people. Visible rays – visible light emitted or reflected by objects; Ultraviolet rays – produced by special lamps and very hot bodies, like the sun. Question 63. They also underscore the need for consumers to take certain commonsense precautions to use microwave ovens only as manufacturers prescribe. Our eyes are sensitive to this range of wavelengths. Only dishes and containers specifically designed for microwave cooking should be used. Save my name, email, and website in this browser for the next time I comment. However, several precautions need to be taken, specifically with regards to potential exposure to microwaves, thermal burns and food handling.

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