Why, when shaking a medical glass mercury thermometer, the reading of a mercury column begins to fall: operating principle, explanation

This article describes the operating principle of a medical mercury glass thermometer.

A mercury medical thermometer for measuring temperature, although it is already considered a thermometer of the last century, but it is still one of the most accurate and correct. We all use or used it, but few thought about its principle of action. Why does a column start to drop when a medical mercury glass thermometer is shaken? Look for the answer below.

The principle of operation of a medical glass mercury thermometer: what is it based on?

Medical thermometer

A medical thermometer can be found in every home. It is used to measure the temperature of the human body. A mercury thermometer is considered the most accurate instrument in its intended use. All specialists in the field of medicine prefer to use it, due to the minimum error and low cost. But what is the principle of operation of a medical thermometer based on?

  • The thermometer is a design consisting of a measurement scale, a tube and a mercury tank.
  • All components are enclosed in a glass case that provides vacuum and content safety.
  • When measuring temperature, the metal tip in which the reservoir is hidden is heated. Mercury, like any other substance, expands when heated.
  • Excessive heated mercury is pushed through the narrowed neck into the tube. The tube runs along the graduation scale. There you can already see the values ​​of the readings - this is the body temperature.

Remember: Mercury is a toxic substance and hazardous to health. Therefore, such a mechanism as a thermometer requires careful handling. Glass is a brittle material, falling can lead to a violation of the integrity of the case and the release of mercury into the environment.

Why, when shaking a medical thermometer, the mercury column starts to fall: explanation

Medical thermometer

When measuring body temperature with a mercury thermometer, the readings always remain at the maximum value. This is due to the vacuum inside the measuring tube. But why, when shaking a medical thermometer, does the mercury column begin to drop? Here is the answer:

  • When a person shakes a thermometer, the hand sets the direction in which the device and mercury move.
  • Liquid metal has high acceleration. Due to the abrupt stop of movement, mercury continues to move by inertia and enters the storage tank through a narrowed neck.
  • Mercury cannot return back without force.

Important rules to keep in mind:

  • Do not take on the metal nose of the thermometer - the readings will increase when heat is transferred by hand, a fragile element can be accidentally dropped, the wrong direction of movement will be set.
  • When shaking, you need to firmly grasp the rounded upper end, the mercury container should be on the opposite side.
  • Hand movements should be sharp and directed downward from the elbow.

Interesting: The narrowed part of the container, the mercury properties and the surface tension force do not allow the colder substance than in the tank to return back. Therefore, the temperature in the thermometer, if not used, will always be in one parameter.

“Shake a medical thermometer” - glass mercury: why is it needed?

Medical thermometer

Instruments for measuring body temperature, in common people called thermometers, are electronic and liquid (most often mercury). Before measuring the temperature with a mercury thermometer, always say: "Shake the medical thermometer" - why is this needed? Here is the answer:

  • Liquid thermometers are designed so that they must be shaken in order to measure the temperature again.
  • As soon as a person has measured the temperature, mercury is fixed at a certain point and remains in one place.
  • This is due to the fact that the mercury expands as a result of heating and from the tip of the thermometer falls into the area where the numbers are applied.
  • Due to the narrow jumper after the measurement is completed, the liquid itself cannot get back.
  • To do this, shake the medical thermometer. Otherwise, you can begin to measure the temperature from the value of the last measurement and then the readings will be erroneous.

But, if the last measurement stopped at a mark not exceeding 36.0 degrees, then you can measure the temperature without shaking. Usually, the thermometer is shaken to a reading of 34-35 degrees.

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