how do thermometers work?

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Specifically the ones that measure your temperature as opposed to the weather ones. I know about the mercury but is that in the ones you use for your temperature? And how to the touchless ones work?

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5 Answers

Anonymous 0 Comments

Mercury has not been used in thermometers for a fairly long time. Mercury thermometers relied on liquids expanding and contracting with temperature, and many substances other than mercury can do this. Even steel does this! Certain temperature sensors rely on different metals expanding at different speeds.

Thermometers use any technology that they can. Touchless ones use thermal radiation – all objects glow with a light based on their temperature. Hot enough ones glow visible, like the sun, but even you and I glow in infrared light. The thermometer just measures this light, does a bit of math, and tells a temperature.

Other thermometers use changes in the electrical properties of a material, such as it conducting electricity worse when it is hot or generating electricity when it is hot.

Anonymous 0 Comments

Electric thermometers come in 2 flavors:

Thermistors detect temperature by measuring the change in electrical resistance as the probe’s temperature changes, they’re cheap but not that accurate.

Thermocouples work by butting two dissimilar metals against each other. As the metals heat up, the electrons bounce around at different rates in the two metals. This causes a voltage difference between the two metals; we measure this voltage and convert it into a temperature.

Contactless thermometers work by measuring blackbody radiation. Everything that’s above absolute zero emits infrared radiation which is light at a lower frequency. We use a special camera to measure what color this light is and convert it to temperature.

Anonymous 0 Comments

Mercury thermometers work because mercury is a liquid that expands by a very precisely known amount for a given change in temperature (called the coefficient of expansion). Mercury has a very large coefficient of expansion which means its volume increases by a *relatively* large amount for every degree Celsius the temperature increases (and shrinks by an equal amount when the temperature falls).

The bulb at the bottom of the thermometer absorbs some heat from your body, expands and pushes the column of mercury up the tube so you can read it. You could use another liquid like alcohol or water but they have much lower coefficients of expansion which means they would have to use much longer tubes to be equally sensitive.

Wireless thermometers read infrared (heat) radiation coming off an object – like your forehead or a piece of meat on the barbecue. The infrared radiation is focused on an electrical component called a thermopile which creates a small electrical current – the greater the heat, the greater the current. This can be measured and used to generate a display telling you the temperature.

Anonymous 0 Comments

The ones that measure your temperature operate on the same principle as the ones that measure weather temperature, the temperature-dependent expansion of the fluid inside.

Touchless thermometers use an electric eye that can see infrared radiation, which is heat.

Anonymous 0 Comments

Mercury isn’t used in thermometers anymore, it’s usually alcohol now.

Basically, the bulb, the part that goes in your mouth (or anus for rectal thermometers) has most of the alcohol in it. That then expands and pushes the alcohol up, and it’s calibrated in such a way that the alcohol reaches a designated spot for each degree of warming. This is also how mercury thermometers work.

Touchless thermometers work by using a little infrared camera. By measuring the amount of infrared radiation coming off of you, it can gauge your temperature. This camera doesn’t have enough receptors to take an image of anything, just enough to measure the amount of light coming in. Think of it like a camera with just one big pixel