# What is Thermometer: Definition and 84 Discussions

A thermometer is a device that measures temperature or a temperature gradient (the degree of hotness or coldness of an object). A thermometer has two important elements: (1) a temperature sensor (e.g. the bulb of a mercury-in-glass thermometer or the pyrometric sensor in an infrared thermometer) in which some change occurs with a change in temperature; and (2) some means of converting this change into a numerical value (e.g. the visible scale that is marked on a mercury-in-glass thermometer or the digital readout on an infrared model). Thermometers are widely used in technology and industry to monitor processes, in meteorology, in medicine, and in scientific research.
Some of the principles of the thermometer were known to Greek philosophers of two thousand years ago. As Henry Carrington Bolton (1900) noted, the thermometer's "development from a crude toy to an instrument of precision occupied more than a century, and its early history is encumbered with erroneous statements that have been reiterated with such dogmatism that they have received the false stamp of authority." The Italian physician Santorio Santorio (Sanctorius, 1561-1636) is commonly credited with the invention of the first thermometer, but its standardisation was completed through the 17th and 18th centuries. In the first decades of the 18th century in the Dutch Republic, Daniel Gabriel Fahrenheit made two revolutionary breakthroughs in the history of thermometry. He invented the mercury-in-glass thermometer (first widely used, accurate, practical thermometer) and Fahrenheit scale (first standardized temperature scale to be widely used).

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1. ### Calculate ideal-gas temperature of a material

Here is the table As far as I can tell what we have here are four constant-volume thermometers (each column represents a thermometer). These thermometers work by having a certain constant volume of some specific gas in a bulb. We immerse the bulb in whatever temperature we would like to measure...
2. ### I Constant length metallic wire as a thermometer, using tension?

I posted another question about a thermodynamic system with three coordinates, namely, that of a metallic wire. We can describe that system with temperature, wire tension, and wire length. The result derived in that question was that the partial derivative of wire tension relative to absolute...
3. ### Calculating Copper Wire Gauge for Resistance Thermometer Bridge Circuit

a. The resistance thermometer bridge circuit shown in FIGURE 1 has a designed maximum temperature of 200°C, ignoring the effects of connecting wire resistance. If the connecting loop is 250 m determine the smallest gauge (swg) of copper wire which must be used if the indicated maximum...
4. ### How could the discrepancy be reduced between the two readings?

I am able to solve part (a) using the relationship ##\frac {P_1} {T_1} = \frac {P_2} {T_1}##, where ##T_1 = 273.16## since its the triple point of water and ##T_2 =T_s## ##(T_s = ## melting point of sulphur). I use the two readings for thermometer A to get ##P_1## and ##P_2## as mentioned in the...
5. ### Sensitivity of the liquid-in-glass thermometer

Question description: How could we increase the sensitivity of a liquid-in-glass thermometer such as the mercury thermometer? What is the basic principle for each method ? There are some options: 1.Increase the size of the bulb. 2. Use thinner glass wall outside the capillary tube. 3. Decrease...
6. ### MHB Maths in Temperature and ideal gas Thermometer

Hi, I didn't understand the maths involved in the below article in regard to temperature and ideal gas thermometer. If any member knows it, may reply me. If triple point of water is fixed at 273.16 K, and experiments show that freezing point of air-saturated water is 273.15 K at 1 atm...
7. ### Why the alcohol thermometer is less precise than the mercury one?

Hi, Why the alcohol thermometer is less precise than the mercury one? If I remember correctly, it is because the thermal expansion coefficient of alcohol is not constant, but I am not sure. Thank you for your time. Regards, ORF
8. ### Misc. What is the best piezoresistive material for a DIY strange thermometer?

I am thinking to make a strange thermometer, based on the thermal expansion of a small aluminium-like rod/cylinder. I would attach one end of this aluminium rod to a vertical ceramic wall, and the other side would push against a piezoresistive material. I would then measure the resistance of...
9. ### IR thermometer vs thermal imager

Isn't it both use the same exact principle? An infrared thermometer versus a thermal imager? Why is it that the thermal imager is not for body temperature (as indicated below) while the infrared thermometer is for body temperature. I think they both scan the same blackbody of the physical body.
10. ### Platinum resistance thermometer and Kirchoff's Laws

Hi, I found this question/s online and I was wondering if somebody was able to explain the answer given, specifically the first bit that says R1/(R1+R2) = R4/(R3+R4) (is this something to do with an equivalent resistor to replace the two in series on each side? But why are R1 and R4 the...
11. ### Calculating the Gauge of a Copper Wire for a Thermometer Bridge Circuit

Hi All, Really struggling to get my head around what I'm doing wrong - every time my answer of wire diameter comes out too small for what's included in the table of SWG. I must be doing something wrong somewhere - my attempt is below. Any help is very much appreciated.
12. ### Understanding a simple statement regarding the measurement of temperature

Summary: 1.In the context of calibrating a scale to correlate volume change with temperature, my book states: "Since all substances change dimensions with temperature, an absolute reference for expansion is not available." What do they mean by an absolute reference in this instance? My...
13. ### Temperature Measurement: Are All Thermometers Created Equal?

What is the difference in temperature with different thermometers for the same object? Thanks !
14. ### Infrared thermometer working principle

So, as far as I understand IR thermometer works by measuring light irradiance coming from an object (in the IR spectrum) and then calculating the object temperature using Stefan's law. Since the irradiance falls like 1/r2 with distance, I am wondering how it takes distance into consideration...
15. ### Thermodynamics of a Constant Volume Gas Thermometer

Homework Statement A constant volume gas thermometer contains a gas whose equation of state is (p+\frac{a}{V^2_m})(V_m-b)=RT and another, of identical construction, contains a different gas which obeys the ideal gas law, pV_m = RT. The thermometers are calibrated at the ice and steam points...
16. ### Understanding Mercury and Thermometer: The Science Behind Temperature Expansion

Why does mercury in a thermometer expands when we increase the temperature but it doesn't go down after cooling? Why does it just stay there?
17. ### Thermometer/ reproducible thermal phenomena

What are reproducible thermal phenomena that are used to calibrate thermometers?
18. ### Platinium Resistance Thermometer

Homework Statement In the interval between the freezing point (ice point) of water and 700.0deg-C, a platinum resistance thermometer is to be used for interpolating temperatures from 0 °C to the melting point of zinc, 692.666 K. The temperature, in Celcius or Centigrade, is given by a formula...
19. ### Temperature in Constant volume gas thermometer.

In the constant volume gas thermometer, T (°c)=[P(T)-P(f)]×100/[P(b)-P(f)] (P(T) means gas pressure at T°c P(b) and P(f) for the water's boiling point and freezing point) Is it right?
20. ### Can a Thermometer Be Calibrated Without Using the Formula Provided?

How do we caliberate a thermometer by cross multiplying without using the formula
21. ### Solving a Spirit-in-Glass Thermometer Problem

Homework Statement The "spirit-in-glass thermometer", invented in Florence, Italy, around 1654, consists of a tube of liquid (the spirit) containing a number of submerged glass spheres with slightly different masses (see the figure below). At sufficiently low temperatures all the spheres float...
22. ### Small LED Thermometer - Beginner Electronics

Hi, I'm a freshman in college and a beginner in electronics. Does anyone know of a way to use a micro analog thermometer to change the color of a small LED light once it hits a certain temperature. I am looking to make this on an extremely small scale.
23. ### Thermometer touching the floor and a carpet

Homework Statement A thermometer touches the floor and the other touches a wool carpet lying on the floor. what will the two thermometers show, the same or different temperatures Homework Equations Two materials touching each other the heat moves from the warm to the cold one The Attempt at a...
24. ### Find Temperature Formula for Varying Thermometer

Homework Statement What is the formula that allows you to find the temperature of any given thermometer that varies its temperature with some property? For example is a pressure of 10mmHg means 0degC, what would the pressure be at 50degC? Homework Equations This is what I'm looking...
25. ### Temperature Outside Without Thermometer

Is there a way to determine the temperature outside without using a thermometer? Any formulas I could use?
26. ### Constant Volume Gas thermometer

Hi, Does it make a difference if you use nitrogen gas or oxygen gas or hydrogen gas in the bulb ? Or they all give the same readings given that an arbitrarily chosen constant if found for each ? Many Thanks! :)
27. ### Infrared phototransistor to infrared thermometer

I am designing a tyre temp monitoring system for my Final year project and I would like to know if it is possible to somehow modify a infrared phototransistor to be able to measure an objects temperature in a range of -20 - 120 C. Any suggestions would be greatly appreciated.
28. ### IR thermometer calibration source

Hi, I currently have a black body calibration source which I use for work. It works great, I can calibrate all the IR thermometers just fine, however it isn't a simple quick "check". The IR thermometers are the ratio type in that they measure two wavelengths and using the ratio it can work out...
29. ### The positioning of the thermometer

Hello, I am instructed by my chemistry professor to design an experiment to measure the temperature at which a saturated solution of Sodium Nitrate will begin to boil. If the reagents are pure this temperature will be constant . Can someone tell me why does the lab instructor suggests...
30. ### IR thermometer pointed up into a cloudy sky?

A physics stack question asks why when the air is hotter then your body thermodynamics allows your body to operate as a heat engine as a heat engine must have a sink for waste heat. See question here, http://physics.stackexchange.com/questions/59316/human-as-a-heat-engine Part of the answer is...
31. ### Problems with thermometer

Homework Statement Explain why it would not make sense to use a full-size glass thermometer to measure the temperature of a thimbleful of hot water. Homework Equations Concept of thermal equilibrium The Attempt at a Solution When a thermometer is in contact into a thermal system...
32. ### Thermometer stem correction with pressure

Hi everyone, So I'm a bit stuck in my physics lab report. I have to make a correction to the temperature read in the laboratory (ex:155.2C) because our room pressure was 742.1mmHg and not 760mmHg I'm guessing. I've tried researching this for a while now but I can't seem to find an easy...
33. ### The problems of the isotope paleo thermometer

In some threads around here I have hinted to problems with the use of 'water' isotope ratio's (δ18O, δ2H aka δD) as thermometer of past temperatures. This could become a dense thread, so I'll give the conclusion first: The isotope ratio's in ice cores and other records of meteoric water are...
34. ### Gas Thermometer. Not dependent on gas?

Hello Guys! I was wondering if anyone can tell me why is it that it doesn't matter what gas we are using in the gas thermometer? Will it still be standardized for calibration if we use different gases? Thanks.
35. ### Acquiring Data from a Digital Thermometer

Let me preface this by saying that I know very little of circuitry, signals, etc. I have also Googled/searched the forum for help using keywords that are related to this project but also vague enough that I could not find any useful results. I have a friend interested in how the temperature...
36. ### Need specific IR thermometer model for experimental physics lab

I work in a nano-optics group, and need an IR thermometer with certain specifications. Online I have only come across cooking thermometers and industrial thermometers, so I need help finding one for a physics experimental lab setup. Specifications: - high accuracy, and pin-point surface...
37. ### Expansion of mercury in a thermometer

I think that I’m doing this problem correctly, but the answer seems a bit unreasonable. Can someone else check my work? A thermometer has a quartz body within which is sealed a total volume of 0.400cm^{3} of mercury. The stem contains a cylindrical hole with a bore diameter of 0.10mm. How far...
38. ### Problem involving mercury thermometer

Homework Statement A mercury thermometer contains 7.5 mL of mercury. If the tube of the thermometer has a cross-sectional area of 1.2 mm2, what should the spacing between the °C marks be? (The volume expansion coefficient for mercury is 1.81 x 10-4 °C−1.) Homework Equations ΔV=βV0ΔT...
39. ### How does a IR thermometer work?

was just wondering... Do IR thermometers measure the temperature of an object via the intensity or wavelengths of emitted light? I've heard that you can measure the temperature of clouds with them, why doesn't the IR light emitted by the air in between the cloud and the detector confuse...

I am urgently need help about it(title) Radiation thermometer can be categories into how many types ? Is it mainly separate into Infrared Pyrometer and Optical Pyrometer only ?
41. ### Constant-volume gas thermometer

Homework Statement The pressure in a constant-volume gas ther- mometer is 0.811 atm at 100◦C and 0.5 atm at 0◦C. A) What is the temperature when the pressure is 0.656922 atm? Answer in units of ◦C. B) What is the pressure at 138◦C? Answer in units of atm. Homework Equations...
42. ### Finding the time constant of a thermometer

The time constant of a thermocouple is to be found by exposing it to a step change. Then the thermocouple and a thermometer are exposed to a ramp function and measurements from each are taken simultaneously. The time constant and its uncertainty for the thermometer are to be found. I...
43. ### Pressure, constant volume gas thermometer, and thermodynamics

Just a note before I start off, this was the first line on this homework assignment: "If you have not studied this yet you can do this problem after reading about it in your textbook."... I've honestly tried reading about this stuff, but our teacher hasn't even started thermodynamics yet...
44. ### Working of a Constant Volume Gas Thermometer

How a constant volume gas thermometer works? In "Thermodynamics An Engineering Approach" by Cengal, author says that this type of thermometer is usually filled with Hydrogen or Helium and We use Constant volume gas thermometers for measuring temperatures near absolute zero. Now if volume is...
45. ### Good gift for a friend: infrared thermometer?

I was thinking about getting my friend one for his bday. Does anyone play around with these? I was thinking he could use it to perfectly cook meats on the grill or test the temperature of a pan to make pancakes, etc. Are they really useful or just overkill that people never end up using if...
46. ### Sensitive quick digital thermometer

Hi, I am wondering if anyone can advice on which kind of digital thermometer would be most suitable for the following conditions: 1. It should quickly be able to detect a sudden increase in temperature. The actual temperature is not important, only the detection of a sudden change in...
47. ### Constructing An Electric Thermometer, making it Display the Temperature

Hi! I was wondering if someone could help me understand how to construct an Electric Thermometer so it shows the right Temperature. I have this text from my Teacher to guide me: The temperature sensor provides an output signal which namely is proportional to the temperature, but the...
48. ### Accurate, Affordable Digital Thermometer?

I'm looking for an accurate and reasonably priced digital thermometer. Our lab has lots of cheap models that provide precision of 0.1 C but are only accurate to +/- 1 C. I can lump them together in a room and get a range of about 3 C. Some sellers don't even provide the accuracy information on...
49. ### Understanding How Infrared Thermometers Work

You know those hand held laser gun thermometers , I was reading how they work and it says that the material you point it at is emitting infrared photons , ok so does the gun shoot infrared photons at the material and then they bounce back and it measures the change in energy or does it just...
50. ### Fire Detecting Thermometer?

Is there a way that I could create a fire detecting thermometer that would detect a fire if the temperature went above a certain point? For example, if a thermometer went above 200 degrees C this would signal a fire? How would I create this?