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Microwave Turntable
Percy Spencer's oven, already published, heats food with microwaves in a metal cavity - and a metal cavity holds standing waves, so the food cooks in stripes: scalding in one place, cold 30 mm away. George Schroeder at General Electric named that problem and added the rung every oven now has.
**US 2,632,838**, "Ultrahigh-frequency electromagnetic radiation heating method and apparatus", Schroeder, assigned to General Electric, filed 4. March 1948, granted 24. March 1953: because the standing waves make "uneven heating", the oven is given "a movable material supporting element" so the heating is spread evenly through the food.
**You map the hot spots with marshmallows**, measure the wavelength between them - and get the speed of light out of your kitchen - then compare heating with the turntable on and off. Nothing about the oven is modified or defeated.
Beginner
90 minutes
Instructions
1
1
Read the oven
Read the oven
The plate on the back gives the frequency, almost always 2450 MHz. Note it. Take the turntable's glass plate and roller ring out, and lay the plate upside down or on a ceramic tray so nothing turns.
Tools needed:
Ceramic Tray2
2
Lay a field of marshmallows
Lay a field of marshmallows
Cover the tray with marshmallows in a single close layer. Put it in the middle of the oven.
Materials for this step:
Marshmallows1 pack3
3
Heat briefly and look
Heat briefly and look
Heat for 20 to 40 seconds at full power - stop the moment patches start to swell and brown. Take the tray out with a cloth. Melted patches mark where the field piles up.
Tools needed:
Stopwatch4
4
Measure the spacing
Measure the spacing
Lay the ruler across the tray and measure centre to centre between neighbouring melted patches, four times, in the direction the rows run.
Tools needed:
Steel Ruler5
5
Turntable on, turntable off
Turntable on, turntable off
Put the roller ring and plate back. Set seven equal cups of 50 ml water in a line across the plate; heat 60 seconds with the plate turning and read each with the infrared thermometer. Repeat with the plate resting on an upturned bowl so it cannot turn.
Tools needed:
Infrared Thermometer
Graph Paper6
6
Wavelength, light speed, evenness
Wavelength, light speed, evenness
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7
7
History & Context
History & Context
**What the patent specifies:** an ultra-high-frequency heater with a movable support that carries the load through the cavity's uneven field, spreading the heating evenly. **Modern build (derived):** measurements in an unmodified oven.
Some later ovens replaced the turntable with a rotating metal stirrer in the waveguide, which moves the pattern instead of the food - useful where a flat oven floor matters. The limits are the same either way: a standing-wave oven never heats perfectly evenly, which is why recipes say to stand and stir.
Materials
1- 1 packPlaceholder
Tools Required
5- Placeholder
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