Electric Current through a Microwave Oven

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Edited by Glenn Elert -- Written by his students
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Bibliographic Entry Result
(w/surrounding text)
Standardized
Result
Cutnell & Johnson. Physics. 1998. "A 1650 W toaster, a 1090 W iron, and a 1250 W microwave oven are turned on in a kitchen. As the drawing shows, they are all connected through a 20-A circuit breaker to an ac voltage of 120 V." 20 A
Energy Through Our Lives. WEEP Education Program. 2002. "The information on the label tells us that the microwave oven needs 120 volts of electricity in the form of alternating current to operate, and draws 5 amps of current during its use." 5 A
GE Manual. Models: GLMB186KS, GLMB186KB, GLMB186KC. Year:2003.
Installation Requirements:
Power Source 120 AC 60 HZ
Line Current 13.6 Amps 1550 W
Over Current Protection 15-20 Amps
Requires 120 volt, 15-20 amp parallel
Working voltage 108-132 VAC
13.6 A
Encyclopedia of Science and Technology. McGraw Hill. Vol 11. 1982. "The microwave power, supplied by a magnetron is at a frequency of 2.45 GHz with rated power from 350 to 750 Watts."
[I = P/V = 750 W / 120 V = 6.25 A]
[I = P/V = 350 W / 120 V = 2.92 A]
2.92 – 6.25 A
Frigidaire FAQ's. "Microwave oven must be plugged into its own 15 ampere circuit." < 15 A

Millions of homes in America are equipped with microwave ovens. Why? Because they cook food incredibly quickly. A microwave oven is an appliance that uses electromagnetic energy to heat and cook foods. A microwave oven uses microwaves. Microwaves are very short radio waves commonly employed in radar and satellite communications. In microwave ovens the most commonly used radio frequency is 2,500 megahertz. When concentrated within a small space, these waves efficiently heat water and other substances within foods. Microwaves cook food rapidly because, unlike conventional ovens, they heat only the food and not the air or the oven walls. That is because radio waves are absorbed by waters and fats. The heat spreads within food by conduction. The microwaves produced pass through most materials easily, but they are absorbed by water. The water molecules begin to vibrate rapidly and produce heat, which in turn cooks the food.

In a microwave oven, electricity enters the microwave oven through a series of fuse and safety protection circuits. Setting the oven timer and starting a cook operation extends this voltage path to the control circuits. The control system generates a signal that produces a voltage path to the high-voltage transformer. The high-voltage transformer serves to increase the typical household voltage, of about 115 volts, to about approximately 3,000 volts. This powerful voltage is just what the magnetron tube needs to convert the high voltage into waves of electromagnetic cooking energy. The electric current that passes through a microwave ranges from 5-20 AMPs. If only given power, voltage, and/or resistance, the current can be found by the equations V = IR and P = IV, where I (current) is solved for.

Lindsey Tannenbaum -- 2004

Bibliographic Entry Result
(w/surrounding text)
Standardized
Result
SHARP Household Microwave Oven Model R-5A50. Assembled in USA of parts made in USA and Imports. Serial No.159776 Manufactured November 1988. SHARP Electronics Corp. MAHWAH NJ 07430. "12. V.A.C. 7.44 kW 60 Hz Single Phase Output 700 W 2450 MHz. Complies with DHHS Radiation Performance Standards 21CFR Subchapter J." 5.8 A
Microwave Oven. Encyclopedia.com. 2004. "Typical output power for consumer devices ranges from 650 to 1200 watts." 5.410 A
Davidson, Homer L. Troubleshooting & Repairing Microwave Ovens USA: McGraw-Hill, 1997: 62. "A home oven should have a reading between 1.6 kV and 4.5 kV (equals 160450 mA.), while commercial ovens have a higher measurement. The voltage might vary from 2.0 kV to 7.0 kV (200700 mA) of the current. Any oven that reads above these figures indicate a leaky or shorted magnetron tube (Table 2-1)." 0.1600.700 A
(magnetron tube only)
TABLE 2-1 Microwave oven current and HV chart
Oven Mfg. Current Mfg. Voltage
Litton 160-300 mA 1.9-2.5 kV
Sharp 200-450 mA 1.9-3.5 kV
Tappan 250-325 mA 1.9-2.2 kV
Whirlpool 240-300 mA 2.0-2.5 kV
Sanyo 200-270 mA 1.8-2.3 kV
0.1600.270 A
(magnetron tube only)
Sprague, Dewey D. A Practical Approach to Microwave Oven Safety. Health Physics Society. 2004. "The high-voltage electrical components (up to 4,000 V DC at 300 mA) are contained in a grounded metal enclosure." 0.300 A
(magnetron tube only)

Microwave ovens can be found in practically every American household. It is a fast and easy device for reheating food. Though so many people own a microwave, do they know how one works?

Microwave ovens use radio waves with a frequency of about 2,500 megahertz to heat food. Water, fats and sugars absorb these radio waves, changing them into heat. One weird thing about radio waves is that not every material will absorb the waves equally. A lot of plastics, glass or ceramics won't absorb them. Metal doesn't work well because it reflects radio waves. This is why conductors are not put in the microwave. Sparking can occur and this could lead to something being burned. My parents used to say, "Uh yeah … that's supposed to happen. It means it's working." So unlike what my parents and probably many American thought when they first purchased a microwave, they can't just stick any container in the microwave oven and expect it to work.

Microwave ovens consume power at a rate of 650 - 1200 watts, which corresponds to a current of 5.410 amps at 120 volts AC. To convert power to current, use the equation …

P = VI

It is stated that if electrical components with voltage up to 4,000 V DC at 300 mA are in contained in grounded metal, then the component is safe to use. Does this go for all microwave ovens, new and old? A reading higher than these numbers means that there may be a leakage, which isn't a good thing and it might not be safe. But then again, how safe are microwave ovens? Is the normal current itself safe? If so, why am I told that to be safe, I should stand far enough away while a microwave is on? (Courtesy of my Earth Science teacher who made the entire class paranoid.)

Anna Ng -- 2004


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