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Why is the bore of the capillary tube of a mercury thermometer made narrow?

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βˆ™ 2011-09-13 15:34:05

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Answer Vapour Pressure and Precisiondh25sThe vapour pressure of Mercury (Hg) is low (0.0017 torr at 25 oC). The vapour pressure is dependent on temperature, thus what you want to measure. As the temperature increases, the vapour pressure increases and the mercury imbibes further up the capillary. If the capiallry radius were larger, the readings would be more difficult to see, i.e. the precision would decrease.

Vapor pressure has nothing to do with how a Mercury thermometer works. As the temperature rises, the mercury expands into a narrow bore, because the volume of the mercury increases. If the bore is very narrow then the extra volume has to go a longer way up the bore to accomodate that volume, so it is more sensitive to small changes of temperature.

2011-09-13 15:34:05
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Related Questions

What is a thermometer bore?

A bore refers to the extremely fine or narrow tube found in a thermometer. It is called a narrow bore or a capillary.


Why does a mercury-in-glass laboratory thermometer have a narrow capillary bore?

To increase the sensitivity of the thermometer, that is, for the thermometer to respond quickly to small changes in temperature.


The capillary tubing has a uniform bore in a mercury thermometer?

yes ! to insure linearity


How does the size of capillary bore of a thermometer affect its accuracy?

As the temperature rises, the mercury expands into a narrow bore, because the volume of the mercury increases. If the bore is very narrow then the extra volume has to go a longer way up the bore to accomodate that volume, so it is more sensitive to small changes of temperature. And it is easier to spot small changes of temperature, and read them from the scale more accurately. But if the scale isn't marked accurately in the first place you are no better off.


Why does clinical thermometer have a narrow bore just above the bulb?

To hold the mercury so you have time to read the patient's temperature.


When the bulb of a thermometer is immersed in a boiling liquid the mercury column first descends and then riseswhy?

It first descends because expansion of the capillary bore and bulb takes place. Soon after that, the mercury absorbs the heat and expand, causing the mercury column to rise.


Why does the clinical thermometer have a thin cappilary bore?

well clinical thermometers have thin capillary because to make the thermometer sensitive - by Tericiona in twitter


Why the mercury level in the thermometer first falls and raidly rises if placed in hot water?

As soon as you place the thermometer heat from the hot water first comes in contact with the glass surface of the thermometer which will expand resulting in a greater volume of the bore (capillary which holds mercury) and the level of mercury descends at first..As the heat from hot water reaches mercury,it expands too, which is followed by volumetric expansion of mercury, an increase in the level of mercury results.


Explain why a liquid clinical thermometer has a narrow bore just above the bulb?

because it does


Describe the structure of a thermometer?

The thermometer consists of a very fine glass tube having a very small bore and is called capillary tube. At one end of capillary tube a very thin glass bulb is provided. The bulb is filled with mercury( most of the times) or alcohol The other end of capillary tube is sealed. The capillary tube is protected by a thick glass tube called stem. On the stem are made markings. These markings are called graduations or degrees.


How should you do to increase the accuracy of the thermometer?

using a thin capillary bore using a thick glass stem


What are five requirements of an accurate mercury-in-glass thermometer?

Small volume of bore in which Mercury is stored, so it responds quickly for a small change of temperatureDouble walled Glass for easy readingMore # of divisionsLess resistence in the movement of mercury in capillary, so it responds fasterConstriction


What is the working and construction of thermometer?

WORKING: Place the bulb of the thermometer filled with mercury in a vessel ov small pieces of ice the mercury will arise in the tube and will come to rest at a certain point.this point shows the melting point of ice. CONSTRUCTION:A thermometer consists of a glass bulb filled with mercury.A cappilary tube arises from this bulb.Due to the narrow bore of the tube a small change in the volume of the mercury becomes significiantly visible.


Why are the thermometers called liquid in glass thermometers?

A so-called "glass" thermometer has a small bore-hole in the center of the glass that has some liquid in it. It's the activity of the liquid in the narrow hole that makes the thermometer a thermometer.


What is a bore on a thermometer?

The bore is the tube thing that the liquid is inside. It goes through the center of the whole thermometer.


Why does a mercury-in glass thermometer first drop slightly when placed in boiling water?

When placed in boiling water, the materials comprising the thermometer respond in the order in which the heat penetrates them. As the heat first permeates the glass cylinder, the cylinder expands, enlarging the bore. For the moment until the mercury is also heated, the constant volume of mercury fills the expanded bore to a slightly lower depth. When the heat reaches the mercury and it also expands, its volume to increase, and the liquid depth rises in the bore.


What is the advantage of having the liquid in a liquid thermometer move up a narrower bore?

The narrower the bore the less liquid (mercury or alcohol) is required so the bulb containing the fluid will adjust more quickly to the temperature being measured. o.k well the narrower bore makes the liquid move slower up the thermometer so the accuracy is better ?????


What is the phenomenon of capillarity?

As we insert a tube with fine bore in a beaker of water then water seems rise in the fine bore even above the level of water in the beaker. This rise is known to be capillary rise. Hence capillarity. This is due to the property, surface tension of water. But as we do the same experiment using mercury, there will be a capillary fall. Any way capillarity is there.


What has greatest capillary action?

The narrower the bore of the tube ,the greater is the capillary action. For example :A sponge retains water (on being dipped in water)is due to capillary action.


Why the capillary tubing has a uniform bore?

As a metering device you need uniformity


How can you make a thermometer more sensitve?

1. Using a larger volume of thermometric liquid. 2. Using a narrower capillary bore. 3. Using a thermometric liquid which expands more for the same change in temperature.


Who invented the Mercury thermameter?

A mercury-in-glass thermometer, invented by German physicist Daniel Gabriel Fahrenheit, is a thermometer consisting of mercury in a glass tube. Calibrated marks on the tube allow the temperature to be read by the length of the mercury within the tube, which varies according to the heat given to it. To increase the sensitivity, there is usually a bulb of mercury at the end of the thermometer which contains most of the mercury; expansion and contraction of this volume of mercury is then amplified in the much narrower bore of the tube. The space above the mercury may be filled with nitrogen or it may be less than atmospheric pressure, which is normally known as a vacuum.


What are the different parts of a thermometer?

A thermometer includes a scale, the bore, the bulb, the steps, and coloured alcohol or as in the past:mercury.


How do you increase the range of a thermometer?

If you're the one designing the thermometer, you could make it longer or make the bore wider. If you've got an existing thermometer, there's not much you can do.


Why is the bore smaller right above the bulb in a thermometer?

This is used in clinic thermomethers to keep the volume of mercury above the bulb when you take it out of the body, otherwise the temperature drop will change the reading of the temperature of the body.