Everyday maths 1 (Wales)

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# 5.2 Understanding temperature

Using the right temperature is often a matter of safety. Many things have to be stored or used in a particular temperature range to be safe. 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.

Figure 39 Warning labels

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

Figure 40 Temperatures in Celsius and Fahrenheit

Note: Fahrenheit is still used in the USA.

Here are some temperatures in Celsius and Fahrenheit:

CelsiusFahrenheit
–180
032
1050
2068
3086
40104
50122

Take a look at the example below for comparing temperatures.

## 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.

Figure 41 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 19: 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.)
CelsiusFahrenheit
100212
150302
200392
250482
300572
350662
1. The thermometer on an old freezer shows the temperature in degrees Fahrenheit.
Figure 42 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.)

CelsiusFahrenheit
–30–22
–20–4
–155
–1014
–523
032
1050
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:
Figure 43 A thermometer

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

CelsiusFahrenheit
032
50122
100212
150302
200392
250482
300572
350662
400752

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 2°F, which you need to find 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.
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