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Temperature and its Measurement - Reading Temperature and Units

Grade 6CBSE

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

🔑Concepts

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Temperature is the measure of the degree of hotness or coldness of an object. It is measured using a device called a thermometer.

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The standard unit of temperature is Kelvin (K\text{K}), but in daily life, degree Celsius (∘C^\circ\text{C}) and degree Fahrenheit (∘F^\circ\text{F}) are more commonly used.

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A Clinical Thermometer is specifically designed to measure human body temperature. Its scale ranges from 35∘C35^\circ\text{C} to 42∘C42^\circ\text{C} (or 94∘F94^\circ\text{F} to 108∘F108^\circ\text{F}).

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The normal temperature of a healthy human body is approximately 37∘C37^\circ\text{C} or 98.6∘F98.6^\circ\text{F}.

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A Laboratory Thermometer is used for scientific experiments and usually has a range from −10∘C-10^\circ\text{C} to 110∘C110^\circ\text{C}.

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To read a thermometer correctly, one must first determine the 'least count' or the value of one small division. If there are 1010 small divisions between 1∘1^\circ marks, each small division represents 110=0.1∘C\frac{1}{10} = 0.1^\circ\text{C}.

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Precautions for reading: Keep the thermometer level with the eye (to avoid parallax error), do not hold the bulb while reading a clinical thermometer, and ensure the bulb is fully immersed in the substance for a laboratory thermometer.

📐Formulae

T(∘F)=(95×T(∘C))+32T(^{\circ}\text{F}) = \left( \frac{9}{5} \times T(^{\circ}\text{C}) \right) + 32

T(∘C)=59×(T(∘F)−32)T(^{\circ}\text{C}) = \frac{5}{9} \times (T(^{\circ}\text{F}) - 32)

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

Value of 1 small division=Difference between two big marksNumber of small divisions between them\text{Value of 1 small division} = \frac{\text{Difference between two big marks}}{\text{Number of small divisions between them}}

💡Examples

Problem 1:

If a person has a fever and their body temperature is recorded as 104∘F104^\circ\text{F}, what is this temperature in Celsius (∘C^\circ\text{C})?

Solution:

Using the formula T(∘C)=59×(T(∘F)−32)T(^{\circ}\text{C}) = \frac{5}{9} \times (T(^{\circ}\text{F}) - 32), substitute 104104 for T(∘F)T(^{\circ}\text{F}): T(∘C)=59×(104−32)T(^{\circ}\text{C}) = \frac{5}{9} \times (104 - 32) T(∘C)=59×72T(^{\circ}\text{C}) = \frac{5}{9} \times 72 T(∘C)=5×8=40∘CT(^{\circ}\text{C}) = 5 \times 8 = 40^\circ\text{C}.

Explanation:

To convert Fahrenheit to Celsius, we subtract 3232 from the Fahrenheit value and then multiply by the fraction 59\frac{5}{9}.

Problem 2:

On a laboratory thermometer, there are 55 small divisions between the 20∘C20^\circ\text{C} and 21∘C21^\circ\text{C} marks. If the mercury thread stands at the third division above 20∘C20^\circ\text{C}, what is the temperature reading?

Solution:

First, find the value of one small division: Value=21−205=15=0.2∘C\text{Value} = \frac{21 - 20}{5} = \frac{1}{5} = 0.2^\circ\text{C}. The mercury is 33 divisions above 20∘C20^\circ\text{C}: Reading=20∘C+(3×0.2∘C)=20∘C+0.6∘C=20.6∘C\text{Reading} = 20^\circ\text{C} + (3 \times 0.2^\circ\text{C}) = 20^\circ\text{C} + 0.6^\circ\text{C} = 20.6^\circ\text{C}.

Explanation:

The reading is calculated by adding the product of the number of small divisions and the value of each division to the lower main mark.

Reading Temperature and Units - Revision Notes & Key Formulas | CBSE Class 6 Science