Questions tagged [microwaves]

Microwaves, broadly defined, are electromagnetic radiation with wavelengths ranging from one meter to one millimeter; or with frequencies between 300 MHz (100 cm) and 300 GHz (0.1 cm). This range includes both UHF and EHF (millimeter waves) and the entire SHF band (3 to 30 GHz, or 10 to 1 cm).

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76
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13answers
28k views

If visible light has more energy than microwaves, why isn't visible light dangerous?

Light waves are a type of electromagnetic wave and they fall between 400-700 nm long. Microwaves are less energetic but seem to be more dangerous than visible light. Is visible light dangerous at all ...
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3answers
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What makes cheese so effective at absorbing microwaves?

Whenever I put a meal in the microwave which contains cheese, why does the cheese get hot before the rest of the meal is heated through?
53
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3answers
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Why is Microwaved mac & cheese burnt where they touch?

After reheating cold about 1.5 oz. of Annie's Mac & Cheese shells for 15 seconds on high power in the microwave, the mac & cheese was burnt black only at certain points where the pasta is ...
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4answers
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Why don't we use infrared light to heat food?

Why don't we use infrared (IR) or even the far IR just to heat food in a microwave oven instead of, of course, the conventional 2.45 GHz microwaves? Don't people call IR heat waves?
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4answers
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How to imagine WiFi signal propagation?

When thinking about how the WiFi signal propagates through a household, can I use the following thought experiment? Assume absolute darkness. Place a strong lightbulb where the WiFi access point is....
27
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3answers
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How do microwaves heat moisture-free items?

Today I learnt that microwaves heat food by blasting electromagnetic waves through the water molecules found in the food. Does that mean food with 0% moisture (if such a thing exists - dried spices?) ...
27
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2answers
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How can wifi penetrate through walls when visible light can't?

I did search the question on Physics S.E considering it would be previously asked. I found this How come Wifi signals can go through walls, and bodies, by kitchen-microwaves only penetrate a few ...
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Why are there different explanations of microwave oven heating, eg dipole alignment vs absorption? Is it quantum vs non-quantum?

There seems to be different explanations of how microwave ovens work. Here are the two basic forms of explanation I've heard: A. As microwaves pass through, the molecule dipoles try to align with the ...
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How does the grid on the microwave oven window prevent microwave radiation from coming out?

If I look through the microwave window I can see through, which means visible radiation can get out. We know also that there is a mesh on the microwave window which prevents microwave from coming out. ...
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6answers
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Could cell-phone radiation cause cancer?

It is very crucial that I ask whether it could and not whether it does. I do not mean to be the least controversial. To my surprise, having read "Physics for Future Presidents" by Richard Muller last ...
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Why do metal objects in microwaves spark?

I heard that electrons accumulate at points on metals, and this clearly explains the arcing phenomenon, but how does a microwave make an electron imbalance on the fork?
15
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5answers
934 views

Why doesn't the escape of electromagnetic waves from a microwave depend on the reference frame, because of the Doppler effect?

If an observer traveling towards a microwave oven at almost the speed of light blue shifts the microwaves enough to be visible light, how can the mesh on the oven door still stop to waves from ...
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Is it really possible to “discover” the speed of light with a microwave oven?

I've seen a number of sites/videos online that describe a method for measuring the speed of light, using a microwave oven and a chocolate bar. For example, this video on youtube. The basic idea is to ...
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Is it possible to shield a camera so as to record from the inside of a running microwave oven?

Would it be possible to create shielding for a camera, allowing it record food being cooked from the vantage point of the inside of a consumer microwave oven without the camera being damaged? ...
13
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1answer
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Can microwaves affect WiFi?

I listen to the radio via my iPad with wifi. When I switch the microwave oven on, the radio cuts out. When the microwave oven is finished, the radio comes back on. (This is 100% reproducible!) So - ...
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2answers
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Should I place a spoon in a cup of liquid before heating it in a mircowave?

Metal objects in microwave ovens are known to be somewhat dangerous. However, my microwave has the following label stuck inside: It seems to imply that this particular oven forbids heating drinks ...
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Do Microwave oven heating times grow linearly with Wattage? Calculating optimal heating time

So this is a completely random and trivial question that was prompted by looking at my microwave oven and the back of a TV dinner and my google searching failed to produce a meaningful answer so ...
12
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1answer
254 views

Why is it that fractal antennas can filter out so many frequencies?

As known, fractal antennas are used for example in cell phones. But why is it that so many different kinds of frequencies can be filtered out of the forest of radio waves surrounding us? Is it because ...
11
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5answers
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How come Wifi signals can go through walls, and bodies, but kitchen-microwaves only penetrate a few centimeters through absorbing surfaces?

The only difference that I know of between kitchen microwaves and WiFi signals is how much power is pumped through them. Why is it that WiFi signals, being 1000 times weaker can travel so much ...
11
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2answers
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What happens in an empty microwave oven?

What it we don't put any food in a microwave oven? I.e. nothing to absorb the microwaves? Would the standing microwave modes in the 3D cavity be reinforced? Would there be too much energy in the ...
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2answers
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Why do microwave ovens use radiation with such long wavelength?

According to Wikipedia: Consumer ovens usually use 2.45 gigahertz (GHz)—a wavelength of 12.2 centimetres (4.80 in). Typically, I put the dish inside the oven in its center. I suspect most people ...
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4answers
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Can we detect whether food has previously been heated in a microwave oven?

An acquaintance told me that she refuses to eat microwaved food because she read that the microwave changes the molecules of the food somehow. Her statement is vague and her sources are dubious but I ...
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How could we see microwave radiation with our eyes?

A few years ago I read a short little article about how big our eyes would have to be to observe microwaves (or any long-wave radiation for that matter). I don't remember enough about the article, or ...
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4answers
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Why do we use microwaves in microwave oven?

We know that any object above absolute zero emits electromagnetic radiation. So hotter the object shorter the wavelengths. In the electromagnetic radiation spectrum radio waves has the longest then ...
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1answer
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Does a domestic microwave work by emitting an electromagnetic wave at the same frequency as a OH bond in water?

I was told once that microwaves work by exciting water molecules in food. Also that this worked because the frequency in the microwave was the same as that in the bond between Oxygen and Hydrogen in ...
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2answers
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Does the cavity magnetron in a microwave oven produce x-rays?

It seems like it should due to bremsstrahlung, since we're talking about electrons with 5-7KeV of energy slamming into the walls of the device, but I've found no information about this online, so I'm ...
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1answer
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Why when I put a teabag into microwaved water does the water fizz? [duplicate]

When I am in a rush, I will heat up water in a cup in the microwave for tea. I usually put the cup on high for 2 mins. When I put the teabag in, the water starts to fizz almost like it is carbonated,...
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2answers
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How can we detect cosmic background radiation?

From what I understand, CMB is the left over radiation from the Big Bang. As all matter, including the Earth, was made during the Big Bang and then as the universe expanded that matter/energy got ...
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Why doesn't visible light generate sparks in aluminum foil when microwaves do?

When aluminum foil is placed in a microwave, I see sparks generated by what I assume is dielectric breakdown. However, if I put aluminum foil in visible light (assuming the same intensity), there are ...
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3answers
522 views

How many photons are in a microwave oven?

I have always had trouble connecting the picture of classical electromagnetism with the idea of photons. To make this connection better I'd like to ask the following question. How many photons, at an ...
6
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1answer
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Microwave oven heating time

It's logical to think that the time it takes a microwave to heat the food would be proportional to the mass heated. But since a microwave is based on dielectric heating, I think that if you increase ...
6
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1answer
534 views

Why can a cellphone ring inside a microwave?

I placed my cellphone inside my microwave. This notwithstanding, my step mother was able to call me, again. Is it a normal thing or I need to change of microwave ? I believed faraday cage of a ...
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2answers
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How can laser communication be faster than microwave?

My textbook states that "Laser communication is much faster than microwave communication." But, how can that be? Both are electromagnetic waves with different frequencies but, how can the speed be ...
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7answers
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Will a microwave heat sand?

I want to cook Turkish coffee on heated sand at school. I have difficulty accessing some easier method of heating, so I was going to try to heat sand in a microwave. It was then pointed out to me that ...
5
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1answer
129 views

What piece of technology is able to record the exact phase of microwaves?

I read that in VLBI, the signals of microwaves are recorded and then later combined. A famous example of this is the Event Horizon Telescope which imaged the black hole. Presumably, the telescopes ...
5
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3answers
113 views

Common microwave absorbing substances

I'm looking to demonstrate to class of students how microwave absorption works, but I need something relatively common which I can easily make into a board. Does anyone have any suggestions for ...
5
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1answer
445 views

Why are magnetron apertures in home microwaves so small?

I'm curious why magnetrons from a home microwave like in the image below can have an aperture between the magnetron cavity and the waveguide that is significantly smaller (2-6mm usually) than the ...
5
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2answers
521 views

Impossible microwave interference?

I was doing a microwave experiment with the following set up: there is a Gunn diode which emmits microwave radiation and a receiver (both work with polarised light). The strange thing is that when I ...
4
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2answers
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Faraday cage for blocking cellphone and wifi signal [duplicate]

Good day, I have created a faraday cage with metal sheet of .5 mm thickness with aluminum foil wrapped outside and inside of the cage. I was happy at first to notice that the cellphone signal goes ...
4
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2answers
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Heating effects of microwaves

I understand the heating effect(dielectric heating) of microwaves. This heating is caused by using a frequency of 2.45 GHz and this is the same frequency at which Bluetooth works and the L and S ...
4
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2answers
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As with infrared pictures, would it be possible to see 2.4GHz waves as light?

I have seen many pictures of stars that were taken in the UV or IR spectrum. Others have pointed out that they are scaled down so as to map to visible elements within our capabilities. Could Wi-Fi ...
4
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2answers
208 views

Microwave oven and heating my sons milk

I heat up my sons milk in the microwave... I use the same volume all the time and always punch in 42 seconds (on high) and his milk comes out the perfect temp every time. However, sometimes he ...
4
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2answers
85 views

Why non-ionizing radiation is non-ionizing?

From Wikipedia I read that non-ionizing radiation "does not carry enough energy per quantum (photon energy) to ionize atoms or molecules". https://en.wikipedia.org/wiki/Non-ionizing_radiation#...
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1answer
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Microwave Ignorance

I have two identical ceramic coffee cups, but when I put them into the microwave (oven) with the same amount of water, for the same amount of time, the handle of one cup is discerningly hotter than ...
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1answer
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Why does the food in the microwave heat up but the bowl doesn't?

I put a 1/4 inch thick clear glass container into the microwave with a plate on top and put it in for almost 5 minutes (there was lots of soup). When It came out the soup was really hot but I could ...
4
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1answer
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Microwaves and Water Molecules: Radar vs Cooking

I am studying microwave radiometry and confused over this apparent contradiction: Microwaves emitted at 2.45 GHz (~15 cm) are absorbed by water molecules, causing the molecules to rotate under the ...
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5answers
3k views

Why do I lose signal in a train but not in a car?

Mobile phone signals seem to be interrupted very often when travelling by train. I have been wondering why exactly, and found two reoccuring explanations online: The train acts as a faraday cage, and ...
3
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1answer
949 views

If a microwave oven disk rotates to warm up food, why doesn't it go up/down/sideways?

This has been in my mind for a while... Well, actually everytime I heat any food with a greater amount of liquid in it: a microwave oven warms up food by inducing polar molecules in the food to ...
3
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1answer
196 views

How come a mobile phone signal is blocked by aluminium foil, but Wi-Fi gets through?

Major puzzle for me. I have done a demonstration in lectures for years now, where I show that a mobile phone call can be blocked by wrapping the phone in a single sheet of standard Aluminium kitchen ...
3
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1answer
2k views

Does a microwave resonantly excite the rotational levels when cooking?

Wikipedia states there is no resonance absorption, but says at the same time that the molecules are oscillating like dipoles, which is kind of the same if you are exciting the rotational levels ? The ...

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