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Everyday maths 1
Everyday maths 1

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5.2 Understanding temperature

Using the right temperature is often a matter of safety. For example, a piece of machinery may not be able to operate properly below a minimum temperature or above a maximum temperature, or a jar of tablets may include advice on its label about what temperature it should be stored at.

Described image
Figure _unit3.5.6 Figure 41 Warning labels

Temperatures used to be shown in degrees Fahrenheit. You will still see these measures sometimes. For example:

Described image
Figure _unit3.5.7 Figure 42 Temperatures in Celsius and Fahrenheit

Box _unit3.5.2

Note: Fahrenheit is still used in the USA.

Here are some temperatures in Celsius and Fahrenheit:

Table _unit3.5.1
Celsius Fahrenheit
–18 0
0 32
10 50
20 68
30 86
40 104
50 122

Take a look at the example below for comparing temperatures.

Case study _unit3.5.2 Example: Safe storage

You have instructions with chemicals sent from the USA that they must be stored at between 50 and 70°F. The thermometer on the storage tank shows the temperature in degrees Celsius.

Described image
Figure _unit3.5.8 Figure 43 Using a thermometer in safe storage

Are the chemicals stored safely?

Method

Looking at the temperature comparison chart, 13°C falls in the following range:

  • 10°C = 50°F
  • 20°C = 68°F

13°C falls between 10°C and 20°C, meaning that it is also in the range between 50°F and 68°F. The chemicals are stored safely.

Now try the following activity. Remember to check your answers once you have completed the questions.

Activity _unit3.5.2 Activity 13: Celsius and Fahrenheit

  1. A recipe for meringue says you must cook it at 150°C. Your cooker shows temperatures in Fahrenheit. What should you set it to? (Use the conversion chart below to help you.)
Table _unit3.5.2
Celsius Fahrenheit
100 212
150 302
200 392
250 482
300 572
350 662
  1. The thermometer on an old freezer shows the temperature in degrees Fahrenheit.
    Described image
    Figure _unit3.5.9 Figure 44 Converting temperatures on old thermometers

    A pack of food has a warning that it must be stored between –12°C and –25°C. Is the food stored safely? (Use the conversion chart below to help you.)

Table _unit3.5.3
Celsius Fahrenheit
–30 –22
–20 –4
–15 5
–10 14
–5 23
0 32
10 50
  1. A machine must be turned off if the temperature rises above 600°F. Using a Celsius thermometer, you find out that the temperature of the machine is:
    Described image
    Figure _unit3.5.10 Figure 45 A thermometer

    Is it safe to leave it turned on? (Use the conversion chart below to help you.)

Table _unit3.5.4
Celsius Fahrenheit
0 32
50 122
100 212
150 302
200 392
250 482
300 572
350 662
400 752

Answer

  1. You will see on the conversion chart that 150°C is equivalent to 302°F. The oven would not be marked this accurately, so you should set it to 300°F.
  2. The thermometer shows 1°F, which you need to fine the Celsius equivalent of. Five degrees Fahrenheit is –15°C; –4°F is –20°C. The temperature is between –15°C and –20°C, so the food is stored safely.
  3. You need to find 600°F on the chart. You will see that 300°C is 572°F, and that 350°C is more than 600°F. The temperature on the dial is even higher than this, at 370°C. The machine is therefore not safe and must be switched off.

Summary

In this section you have identified and practised:

  • how to solve problems requiring calculation incorporating temperature
  • the correct way to read temperature and the difference between the units used.