In this explainer, we will learn exactly how to properly use thermometers to measure up the temperature of liquids and also gases.

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Temperature is a measure of how warm or cold a substance is. We deserve to measure the temperature that a substance using an instrument called a thermometer. There are two species of thermometer: analog thermometers and also digital thermometers.

The diagram below shows one analog thermometer.


Analog thermometers are generally made of glass with a red-colored fluid inside. The fluid rises or drops as the temperature that the environment goes up or down. A temperature scale, typically in degrees Celsius or levels Fahrenheit or both, is printed on the thermometer.

Looking carefully at the thermometer, we view marks corresponding to particular temperature values. The note closest come the height of the red fluid is the temperature we read.


To measure the temperature the a fluid accurately using an analog thermometer, there room several important things come remember.

Submerge the bottom of the thermometer, called the bulb, in the liquid to it is in measured. Ensure the the bulb does no touch or gain close to any kind of other product such as the political parties or bottom of the liquid container; if the does, the thermometer will certainly be measure the an unified temperature of much more than one object, rather than the temperature of the substance of interest.

While stop the thermometer steady, offer the red fluid time come rise, fall, or continue to be at the same level. An analog thermometer takes time to readjust to the surroundings. Before we deserve to read the end the measured temperature, the height of the red liquid should not be an altering at all.Holding the thermometer upright, we set our vision level with the top of the red liquid. We stop looking up or down at the optimal of the liquid, due to the fact that that can trick ours eye into seeing an not correct level and recording an untrue temperature.

Looking closely, us may notice that the red liquid has a curved form to the surface. This is dubbed a meniscus (plural: menisci). Generally, a meniscus deserve to curve upward or downward. Menisci the curve up are dubbed convex, and also those curving under are referred to as concave. In either case, when we do a measurement, us look because that the middle of the meniscus and also use that as the fluid level come compare with the temperature clues on the thermometer.

The temperature note closest to the level of the center of the meniscus is the temperature we record as our reading.

A digital thermometer works in much the same method as one analog thermometer. It likewise has a temperature-sensitive bulb that should be submerged in the fluid or gas gift measured. And it too needs some time to reach a steady temperature reading.

Unlike an analog thermometer, a digital thermometer merely reads out the measured temperature. Therefore, errors in interpreting the measure temperature are less likely utilizing a digital thermometer.

Let’s now think about a few examples of acquisition temperature readings, explaining in some instances why those readings are incorrect.

Example 1: reading a Thermometer because that Temperature in degrees Celsius

The diagram reflects a thermometer being used to measure the temperature the the waiting outside. What value does the thermometer offer for the temperature?


We want to review the temperature measure by this analog thermometer. That temperature corresponds to the noting that lines up most very closely with the optimal of the red fluid in the thermometer.

Looking closely, we watch that the top portion of the red fluid is curved, denote a meniscus. The middle of the meniscus, where it is flat, currently up v the note just listed below 10∘C. Each mark represents one increment of 1∘C, so this thermometer is reading a temperature of 9∘C.

Example 2: analysis Thermometer Temperature to the Nearest Degree

The figure shows a thermometer that has actually been left outside in the shade on a hot day. What temperature analysis does the thermometer provide to the nearest degree?


This thermometer steps temperatures on the Celsius scale. The level the red liquid within the thermometer suggests which temperature to record. We have the right to see that the level the the liquid lies in between two temperature values: 29∘C and 28∘C.

The level is closer, though, come the 29∘C mark. To the nearest degree, then, the thermometer’s temperature reading is 29∘C.

Example 3: analysis a Temperature Exceeding a Thermometer’s Scale

A thermometer is inserted in a pan include a mixture the fruit juice and also sugar the is gift heated to it is in turned right into jam. The mixture is cook to end 100∘C. The thermometer is in the number shown. What temperature reading does the thermometer give?

100∘C104∘C105∘CIt is not feasible to get precise reading from the thermometer.110∘C


To read the temperature of a thermometer, we need to discover out which mark the red bar lines increase with most nearly. The bar suggests the level that the fluid in the thermometer.

A close-up look in ~ this level shows that it is above the greatest mark on the thermometer. This nearest mark corresponds to a temperature that 104∘C, but we carry out not report this together our answer, because the red bar is outside the variety of temperatures because that which this thermometer is calibrated. Fairly than calculation what the temperature would certainly be if the marks ongoing up the thermometer or report the temperature of the nearest mark, we should report the we have the right to not accurately review this temperature top top this thermometer.

This coincides to choice D.

Example 4: Explaining Why a Temperature reading Is Incorrect

Engy wants to measure the temperature of some water that has been heated to close to its cook point. She supplies a thermometer that has actually been ~ above a table in the room because that an hour. She places the bulb of the thermometer in the water and also immediately reads the temperature ~ above it, as shown in the diagram. She determines that the temperature of the water is 19∘C. I beg your pardon of the following statements describes why this prize is incorrect?

She did not wait because that the reading to stabilize. The temperature that the water is in reality far greater than 19∘C.She should organize the pear of the thermometer just over the surface ar of the water. This is where the temperature is highest.She should submerge the whole thermometer in the water.


We space told that this water has actually been boil to near its cook point, the is, 100∘C, so we instantly know that a analysis of 19∘C is too low.

19∘C is roughly room temperature, and also we room told that the thermometer has actually been ~ above a table in the room for one hour. Due to the fact that Engy reads the measure up temperature automatically after putting the bulb in the hot water, we can form an idea of just how she obtained her result.

During the time it was on the table, the thermometer stabilized come the ambient wait temperature that 19∘C. As soon as Engy choose up the thermometer and also put it in the warm water, she go not allow time for the thermometer come adjust. The analysis that she thought corresponded come the temperature that the water indicated instead the temperature of the room.

This line of thinking suggests option A together the ideal choice.

Option B states Engy should have held the thermometer bulb above the water’s surface. However, she desires to measure the temperature that the water, which needs covering the pear in the water.

Choice C claims that the proper measurement strategy is to submerge the whole thermometer in water, yet this is not important for a thermometer to measure up a temperature accurately. Only the bulb needs to be spanned by the material being measured; submerging the entire thermometer would be impractical and also would make taking specific reading difficult.

Option A best describes the reason for this not correct measurement.

The water at the political parties of the container is hotter 보다 the water in the middle because it is in direct call with the warm container. The mean temperature the the water is lower.Copper conducts warm well, and the warm from the Bunsen burner is carried out through the copper the the container. Since the thermometer is in call with the copper the the container, it is partially measuring the temperature the the container fairly than the water.Convection currents in the water travel up the political parties of the container; thus, the water in ~ the sides of the container is hotter 보다 the water in the middle. The median temperature of the water is lower.


A crucial fact in our problem statement is the the container holding the water is make of copper. Favor all metals, copper is an efficient heat conductor. We have the right to expect the to heat up in ~ a quicker rate than the water.

At any kind of given moment, then, the temperature that the container is likely greater than the temperature the the water. As soon as Amira puts a thermometer into the water in call with the container, she exposes the thermometer come this higher temperature.

The thermometer reading will be based upon some combination of the water temperature and the container temperature. Because the container temperature is higher, the analysis will no accurately reflect the temperature of the water.

The answer finest describing this is option B. Note that option A supposes that the water in the container is fairly stagnant, vice versa, water gift heated this way would move and also mix transparent the container.

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Key Points

Analog and digital thermometers are provided to measure up the temperatures of liquids and gases.To make a correct measurement using an analog thermometer,submerge the thermometer pear in the fluid being measured;allow the thermometer measurement come stabilize;hold the thermometer upright and position the eye to it is in level v the height of the red liquid;if a meniscus is present, take the measure closest come the level that its middle, the flat component of the curve;read the temperature that the note nearest come this level.For a digital thermometer, monitor the first two steps and also then check out the indicated temperature.