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Types Of Thermometers

Heat and Temperature of Class 7

Different Types Of Thermometers

The Liquid in Glass Thermometer: We have already seen that two types of liquid used for thermometer one is known as alcohol and other is mercury. These liquid are contained in sealed glass tube.

Structure

Two basic parts:

  •  The bulb: The first part is the bulb that acting as a reservoir holding the liquid whose volume changes with temperature changes. The Bulb also acts as a sensor ,which is easy to inserted in the body whose temperature is to be measured.
  • The Stem: containing the scale that is measuring the temperature and a capillary through which the liquid can accordingly expand and contract

bulb part of thermometer stem part of thermometer

General Properties

Advantages:

  • They are cheap to manufacture and find in shops.
  • Easy to carry as well as handle it.

Disadvantages:

  • For very high heat this is not useful. Not sensitive it cannot measure rapid temperature changes.
  • The mercury­­glass thermometer:We already studied about mercury glass thermometer that it was invented by German physicist Daniel Gabriel Fahrenheit. To increase the sensitivity in thermometer , there is a shiny bulb of mercury at the end of the thermometer which contains at most 90 percent of mercury .But some part of this is filled with nitrogen or it may be a vacuum.

mercuryglass thermometer

  • Range: Covering a wide temperature range from -38 °C to 356 °C, although the introduction of a gas into the instrument can increase the range to 600 °C or beyond.

Advantages:

  1. Mercury is a naturally shiny opaque liquid .
  2. Mercury does react with glass so donot wet glass. When it moves up and down in the capillary due to cohesive properties of mercury it do not allow to leave any traces on the inside of the capillary.
  3. Mercury is a liquid metal. As a metal it has high conductive properties that allow it to be more sensitive than the alcohol in glass thermometer.

Disadvantages:

  •  Mercury is toxic .
  • The alcohol­­glass thermometer: As a liquid it utilises ethyl alcohol, toluene and technical pentane.

alcohol glass thermometer

  • Range: -200 °C to 80°C, though range tends to be highly dependent on the type of alcohol used.

Advantages:

  • It can measure very low temperatures.

Disadvantages:

  •  Alcohol is transparent therefore it requires a dye to make it visible. Dyes tend to add impurities that may not have the same temperature range as the alcohol making reading difficult especially at the limits of each liquid.
  • Alcohol wets glass.

Laboratory thermometer:

For laboratory use alcohol base thermometer is used.It is also known as spirit laboratory thermometer. This is a 76 mm partial immersion laboratory thermometer and it is designed to be immersed up to the inscribed immersion line.

laboratory thermometer

The markings are black on a white background to make you easy to read the measurements. Laboratory thermometer comes completely with an anti-roll triangle and a case.

Advantages:

  • To measure low temperature b/w 10 - 120 degree Celsius.
  • Used in all lab experiments.

Disadvantages:

  • Misuse of the instrument for other purposes.
  • Leakage of mercury can be dangerous.

laboratory thermometer uses & misuses

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