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Measure - Reading temperature on a thermometer

Grade 3Cambridge (IGCSE)

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

🔑Concepts

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Temperature is a measurement of how hot or cold an object or environment is.

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The standard unit used in the IGCSE curriculum for measuring temperature is Degrees Celsius, written as ∘C^{\circ}\text{C}.

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A thermometer is the tool used to measure temperature. It usually contains a red or silver liquid that rises as it gets warmer.

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To read a thermometer, first look at the scale. Determine the value of each small marking (the interval). For example, if there are 55 small gaps between 00 and 1010, each gap represents 10÷5=2∘C10 \div 5 = 2^{\circ}\text{C}.

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Key benchmarks to remember: Freezing point of water is 0∘C0^{\circ}\text{C}, and the boiling point of water is 100∘C100^{\circ}\text{C}.

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The 'level' of the liquid indicates the current temperature reading. Always read the scale at the very top of the liquid line.

📐Formulae

Temperature=Value on the scale line\text{Temperature} = \text{Value on the scale line}

Interval Value=Difference between numbered marksNumber of small gaps\text{Interval Value} = \frac{\text{Difference between numbered marks}}{\text{Number of small gaps}}

New Temperature=Old Temperature±Change\text{New Temperature} = \text{Old Temperature} \pm \text{Change}

💡Examples

Problem 1:

A thermometer has numbered marks at 10∘C10^{\circ}\text{C} and 20∘C20^{\circ}\text{C}. There are 55 equal small spaces between these two marks. If the liquid reaches the second small mark after 1010, what is the temperature?

Solution:

  1. Calculate the value of each small space: (20−10)÷5=2∘C(20 - 10) \div 5 = 2^{\circ}\text{C}.
  2. Count from the 10∘C10^{\circ}\text{C} mark: 10+(2×2)=14∘C10 + (2 \times 2) = 14^{\circ}\text{C}.
  3. The temperature is 14∘C14^{\circ}\text{C}.

Explanation:

First, find the scale interval by dividing the difference between numbers by the number of gaps. Then, add that interval for every small line the liquid has passed.

Problem 2:

In the morning, the temperature was 12∘C12^{\circ}\text{C}. By afternoon, it rose by 9∘C9^{\circ}\text{C}. What is the afternoon temperature?

Solution:

12+921\begin{array}{r} 12 \\ + 9 \\ \hline 21 \end{array} The temperature is 21∘C21^{\circ}\text{C}.

Explanation:

Since the temperature 'rose', we use addition to find the new temperature.

Problem 3:

The temperature inside a fridge is 4∘C4^{\circ}\text{C}. The temperature in a freezer is 10∘C10^{\circ}\text{C} colder than the fridge. What is the temperature in the freezer?

Solution:

4∘C−10∘C=−6∘C4^{\circ}\text{C} - 10^{\circ}\text{C} = -6^{\circ}\text{C}

Explanation:

To find a temperature that is 'colder', we subtract. When we subtract 1010 from 44, we go below zero to reach −6∘C-6^{\circ}\text{C}.

Reading temperature on a thermometer Grade 3 Notes & Examples