Matter
Temperature and its measurement
Say why touch cannot judge hotness, read a thermometer correctly, and convert a Celsius temperature to the Kelvin scale.
Put your right hand in warm water and your left in ice-cold water, wait a minute, then plunge both into the same bowl of tap water. The right hand reports cool; the left reports warm. One bowl, two answers, and neither hand is lying. Touch is comparing, not measuring — which is why we need a number instead.
Temperature and thermometers
The reliable measure of how hot or cold a body is, is its temperature, and the device that measures it is a thermometer. A clinical thermometer is for human body temperature; a laboratory thermometer is for the rest. Both are marked in degrees Celsius, written °C.
Three scales
Celsius gives degrees Celsius, °C. Fahrenheit gives degrees Fahrenheit, °F — 37.0 °C is the same temperature as 98.6 °F. Kelvin gives the kelvin, K, and it is the SI unit used in scientific work. To go from Celsius to Kelvin, add 273.15.
Have a play
Slide along this laboratory thermometer's scale. Its range runs from one end to the other, and each small step is ten degrees.
Tap anywhere on the line.
Worked example
A laboratory thermometer shows 10 °C between its big marks, and 10 small divisions between them. What is the smallest value it can read?
Read the gap between the two big marks: from 0 °C to 10 °C is 10 °C.
This is the size of the stretch you are about to cut up. Reading it off the wrong pair of marks throws the whole calculation out.
Try it together
Now take a room at 27 °C over to the scale used in scientific work.
Answer with a bare number each time.
1.Which scale's unit is the SI unit of temperature — Celsius, Fahrenheit or Kelvin? Answer with the scale's name.
Have a go
Have a go on your own. Ice-cold water sits at 0 °C. What is that on the Kelvin scale? Answer with a number.
Ready to practise?
Eight questions on what you have just read. Nothing is timed, and you can play as many times as you like.