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Temperature and its Measurement - Laboratory and Clinical Thermometers

Grade 6CBSE

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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Temperature is defined as the measure of the degree of hotness or coldness of an object. The SI unit of temperature is Kelvin (KK), but in daily life, Celsius (∘C^\circ C) and Fahrenheit (∘F^\circ F) are commonly used.

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A thermometer is a device used to measure temperature. It works on the principle of expansion of liquids (usually Mercury or Alcohol) on heating.

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Clinical Thermometer: Designed specifically to measure human body temperature. It has a range of 35∘C35^\circ C to 42∘C42^\circ C. It features a 'kink' or constriction near the bulb that prevents the mercury level from falling on its own, allowing us to read the temperature accurately after removing it from the mouth.

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Laboratory Thermometer: Used for measuring temperatures in science experiments. Its range is generally from −10∘C-10^\circ C to 110∘C110^\circ C. It does not have a kink, so the reading must be taken while the thermometer is still in contact with the substance.

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The normal temperature of a healthy human body is approximately 37∘C37^\circ C, which is equivalent to 98.6∘F98.6^\circ F.

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Digital thermometers are increasingly popular because they do not use toxic Mercury (HgHg) and provide a direct numerical display of the temperature.

📐Formulae

C5=F−329\frac{C}{5} = \frac{F - 32}{9}

T(K)=T(∘C)+273.15T(K) = T(^\circ C) + 273.15

Normal Body Temperature=37∘C=98.6∘F\text{Normal Body Temperature} = 37^\circ C = 98.6^\circ F

💡Examples

Problem 1:

Convert the normal human body temperature of 37∘C37^\circ C into the Fahrenheit scale.

Solution:

Using the formula C5=F−329\frac{C}{5} = \frac{F - 32}{9}, substitute C=37C = 37: 375=F−329\frac{37}{5} = \frac{F - 32}{9} 7.4×9=F−327.4 \times 9 = F - 32 66.6=F−3266.6 = F - 32 F=66.6+32=98.6∘FF = 66.6 + 32 = 98.6^\circ F

Explanation:

The calculation shows how the Celsius scale relates to the Fahrenheit scale, confirming that 37∘C37^\circ C is equivalent to 98.6∘F98.6^\circ F.

Problem 2:

Why can a Laboratory Thermometer NOT be used to measure human body temperature?

Solution:

A laboratory thermometer does not have a 'kink'. As soon as the thermometer is removed from the mouth, the mercury level will start falling immediately due to contact with the cooler air, leading to an incorrect reading.

Explanation:

The 'kink' in a clinical thermometer is essential for holding the mercury level steady so the observer can read the temperature after removal from the patient's body.

Problem 3:

State two precautions to be taken while reading a laboratory thermometer.

Solution:

  1. The thermometer should be kept upright, not tilted.
  2. The bulb should be surrounded from all sides by the substance, but should not touch the bottom or sides of the container.

Explanation:

These precautions ensure that the thermometer measures the temperature of the substance itself and is not influenced by the temperature of the container walls or incorrect viewing angles (parallax error).