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Thermometers

Heat and matter · level 1, lesson 2 of 6

A question to start

Your hands can tell hot from cold, but not exactly how hot. How do doctors and weather forecasters know?

The idea

A thermometer tells you how hot or cold something is. The number is the temperature, and we often measure it in degrees Celsius, written °C.

100 °C: water boils37 °C: your body20 °C: a room 0 °C: ice melts−18 °C: a freezer
  • 0 °C is the temperature where water freezes and ice melts.
  • Below 0 the numbers have a minus sign: −10 °C is colder than 0 °C.
  • 100 °C is where water boils in a pan.

Worked examples

1. Your body. Inside, you are about 37 °C. A doctor checks this when you are ill.

2. A warm day. The weather forecast says 25 °C. That is warm enough for shorts.

3. Ice. It is 0 °C or colder. Ice that is warmer than 0 °C melts.

Try it

  1. What does a thermometer measure?
  2. Which is colder, 5 °C or −5 °C?
  3. Which is hotter, a room at 20 °C or a bath at 40 °C?
  4. At what temperature does ice melt?
Answers
  1. Temperature: how hot or cold something is.
  2. −5 °C.
  3. The bath.
  4. 0 °C.

Common mistake

"−10 is bigger than −5." With a minus sign, the bigger number is colder. −10 °C is colder than −5 °C.

Where it leads