# Tag Info

84

The very first thing you should do is stop using your oven and have it checked out by an authorized repair service. If in fact the oven was operating with the door open, there was a failure of the door interlocks to turn the oven off and a failure of the backup system intended to permanently shut the oven off in the event the interlocks failed which, ...

55

Yes. A simpler way to look at this is that because freezing, as well as resublimation (turning a gas directly into a solid) emits heat. It may seem strange but consider this: you need to put in heat to make water turn from solid into liquid, so the inverse process should transfer the heat in the opposite direction. And that's what it does. In cold air the ...

46

When you pour the hot water in, the air inside the thermos is still quite cold (ambient temperature, approx.) But then when you shake it up the cold air is heated by the hot liquid. Gases expand considerably when heated, approximately acc. the Ideal Gas Law: $$pV=nRT$$ This causes a modest (and harmless) pressure increase in the flask, which is what you ...

44

The magnetron injects microwave radiation at a certain rate. Ignoring losses, that radiation bounces around the walls until it’s absorbed by the food. If you put two burritos in there instead of one, on average there will be fewer bounces before absorption. That means that with two burritos, the average intensity of the radiation impinging on any point is ...

41

A large amount of water (i.e. if the path of light through it is long) will simply start absorbing light, as it's not completely transparent. For smaller amounts, as when pouring it from one container to another, this is mostly negligible. However, there is also surface reflection. A small amount of the incident light will be reflected off by the surface. ...

39

Mist is a suspension of tiny water droplets in air. Light traveling through the mist gets randomly scattered, mainly by bouncing of the droplets. That makes mist far less transparent than bulk water. I don't think mist is literally gray in colour but the fact that mist is far less transparent than pure air (or bulk water) causes it to look the way it does. ...

36

There is another effect here which is significant, as follows. Warm water wants to evaporate, but in a flask-shaped container, the evaporation can take place only at the free surface of the water in the flask. Furthermore, as soon as the boundary layer of air right next to the warm water becomes saturated with vapor, the diffusion of water vapor into the air ...

33

This is just to add an illustration to noah's and Ralf Kleberhoff's answers which correctly point out that refraction is the main reason. Note that although most of the light rays do make it through the water drop, most of them do not continue on the path with the rest of the light bundle, but end up somewhere else. As a result, right behind the drop, the ...

29

Weather is... complex. Turning water vapor to solid releases heat, but this happens up in the sky. You end up with somewhat hotter and drier air somewhere at altitude and some amount of snow that falls down. (If "down" is hot enough, you get rain instead. The rain almost always starts as a snow.) The point is, you may, or more often may not get the ...

28

Although there are already some good answers, I'd like to give it another attempt. Water is transparent in the sense that most of the light that enters some volume of water, also exits at the other end (unless we talk about multiple meters of thickness or lots of dirt in the water). But that doesn't mean that it passes water unchanged. Wherever light enters ...

22

When reading your post, it seemed to me that the most likely explanation for your experience is that the microwave did turn off, but the ventilation did not. You may have mistaken this for the microwave not turning off. If indeed the microwave didn't turn off, you would have felt pain and other sensations immediately. Get a new microwave in that case, and ...

16

Let $P$ be the power (in $\mathrm{Watt}$) the microwave delivers then a simple heating model can be stated as follows. The heat energy $q$ needed to heat an object is: $$q=\varepsilon mc_p\Delta T$$ where $\varepsilon$ is an efficiency factor (for food stuffs with a high moisture/water content $\varepsilon \approx 0.9 - 1$). $m$ is the mass of the object, $... 16 Regarding water droplets collecting on the surfaces of your glasses: Those water droplets backscatter the incoming light in random directions, including ones away from your eyes. This means that any glass lens surface populated with water droplets will appear less bright than it would without the droplets, and the random scattering will obliterate anything ... 11 I mentioned this in a comment, but will post as an answer as well. Apparently, if you run it long enough, some microwaves will keep the fan running for cooling even though the microwave is no longer producing microwaves. My last roommate's microwave did this at the 2 minute mark, and even though the microwave was done cooking, the running fan made it sound ... 10 As a former meteorologist, I do not really agree here. Snow is produced in clouds from water vapour. Broadly speaking (actual cloud microphysics is more complex), you have air flowing up inside clouds. More exactly, clouds are produced when moist air particles go up: the pressure decreases which causes temperatures to decrease too. When an air particle ... 9 For ink to flow out of the pen reservoir, air must be able to flow in, and for ink to not simply drool out of the nib via gravity, some means must be provided to develop a slight negative pressure inside the ink reservoir. Those ribbed features do both, as follows. The air return path goes upwards past the fins, through a very small gap between the tips of ... 8 There are two factors at work here. The first is whether water is "clear", meaning, allows most light to pass through it. And it is, whether it's solid or in a bunch of tiny droplets. The second is whether you can see through it. In order for a substance to be "transparent", it has to have two properties. First, it has to allow a non-... 6 The$absolute\$ humidity is much lower outside. The lenses of your glasses have some thermal inertia, and while you were outside they got pretty cold. When you step inside, where the absolute humidity is higher, a thin layer of air near the lenses cools to below the dew point, and condensation occurs. Then when you go back outside, the droplets evaporate. ...

6

Microwaves do not fill the microwave cabinet uniformly. They form a "standing wave pattern" with high-intensity and low-intensity regions. When something is placed in the cabinet, it distorts the standing wave pattern, so the pattern of hot and less-hot portions can change. The reason most microwave ovens include a rotating turntable is to ...

5

I'm assuming you are comparing a microwave oven to a conventional oven. In short, the reason is microwave energy penetrates the food deeper than a conventional oven. As a result, a small portion will heat up faster throughout in a microwave oven than a conventional oven where the electromagnetic energy absorbed is primarily infrared. On the other hand, ...

5

The difference is really remarkable, but is similar to the difference of intensity in the sound if we touch the floor or the bucket with our finger. The sudden impact produces a very small downward displacement in the point of contact, that spreads as a mechanical wave. The maths are shown here. In the bucket, the energy is mainly dissipated in vibrations (...

5

I guess some light will get reflected at the interface air-water, which will lower the intensity of light through the stream. That and possibly lens-like phenomena which leads to a non-uniform distribution of light intensity on the other side.

4

Warmer-than-average air rises, it cools due to the drop in pressure at higher altitude resulting in adiabatic expansion, and that causes the moisture in it to precipitate and fall as rain or snow. Because the air is rising, heat released up here has a hard time getting back to the surface. The arrival of a warm moist buoyant air mass suddenly replacing a ...

4

Short answer: the acoustic impedance match between the bottom of the bucket and the surrounding air is better than the acoustic impedance match between the floor and air. Sound waves in air are a very non-dense medium moving with large amplitude/distances. Sound waves in the floor are a small amplitude movement of a dense medium. For maximum energy transfer, ...

4

The fact that you can see water at all means it's not completely transparent. Since not all the light goes straight through, there will be a shadow.

3

Your finger is not as opaque as you think it is. This is shown by a heart rate / blood oxygen sensor that works by shining light through your finger tip. Here's a short video.

3

Yes. A fly swatter often charges a capacitor to store the charge for the spark; this capacitor might only leak off slowly when the fly swatter is off. You can still discharge this capacitor yourself by inducing the spark. Then, note the capacitor does not recharge because the fly swatter is off.

3

Let’s calculate. Suppose a cloud approaches at the height of 1 km, its water freezes and it starts snowing. Water releases 333 kJ/kg when it freezes, and a 1 m × 1 m × 1 cm layer of new snow conveniently weighs about a kilogram. Consider one square meter of area. Each centimeter of snowfall means 333 kJ of heat was released above it. How much could it have ...

3

Bucket acts as some sort of a drum, where the membrane is resonating up and down. But the floor only squeezes up and down. The bucket has more room for resonating and resonates more than the floor.

2

The other answers are right--this is just to explicitly point out the reason that it feels worse when 30 people stand on your hand than when your body is subjected to an equivalent amount of hydrostatic pressure. The 30 people squash your hand like a ball of dough in a tortilla press, squeezing parts of it out the sides. Hydrostatic pressure, on the other ...

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