thermometers

• Natuurkunde
• Middelbare school
• vwo
• Leerjaar 2

What does a thermometer measure?

1. heat
2. temperature
3. energy
4. cold

What is the SI unit of temperature

1. centigrades
2. Fahrenheit
3. Kelvin
4. degrees Celcius

Temperature is measured by a thermometer.

Find out why by doing the following experiment:

Fill one cup with water and ice cubes

Fill one cup with normal tap water

Fill one cup with warm water

Put your left hand or just a few fingers first in the ice cold water and then in the tap water

Put your right hand first in the warm water and then in the tap water.

What do you notice?

Fun fact!

Celsius did not say that boiling water was 100 degrees, but 0 degrees. And freezing water was 100 degrees.

He probably did this to avoid negative numbers.

It can be freezing cold in winter in Sweden..........

Explain in your own words how Celsius made his thermometer.

Celsius decided that water boiled at 100 degrees. What if he decided that water boils at 50 degrees. What would then be room temperature and what would be your body temperature?

thermometer

A thermometer  has a resevoir, a capillary tube and a graduated scale.

These days the liquid in a thermometer is alcohol instead of mercury. Can you say why?

Fahrenheit

As you can see in the picture the scale on the right differs from the scale on the left.

In the next slide is a video about Fahrenheit.

Clinical thermometer

The graduation goes from 35 to 42 degrees. Why?Because the range of the body temperature is between 35 and 42 degrees.

At the place of the arrow is a kink in the capillary. This prevents the liquid to fall down quickly. The air has assumingly a temperature of 20 degrees. Without the kink you would not have time to read the thermometer!

To let the mercury back in the bulb you need to shake the thermometer.

Kelvin

Lord Kelvin uses another scale. He did a thought experiment and found out that there cannot be a lower temperature than -273.15 degrees Celcius. He named it absolute zero. He used the same graduation as Celcius. So an increase of 1 degree Celsius is an increase of 1K. And therefore 0 degrees Celsius is 273.15K.

For calculations we use 0K = -273 C

278K

280 C

300K

5 C

553K

27 C