3-8 Calculations with temperature (3.3)

• Natuurkunde
• Middelbare school
• havo, vwo
• Leerjaar 2

Calculations with temperature (3.3)

Celsius and kelvin

Celsius (used almost everywhere in the world)

- Two fixed points

- Melting ice = 0 ⁰C

- boiling point ofpure water

           = 100 ⁰C

Kelvin

Physicists prefer kelvin

Starts at absolute zero

- 0 K

- 0 ⁰C = 273 K

- Boiling water 373 K

Thermometer

- Uses a liquid (e.g. coloured alcohol 

    or mercury)

- liquid expands as temperature increases.

- digital clinical thermometer: The sensor is an electric circuit where voltage accross the sensor 

varies with temperature. The voltage 

is converted to a temperature.

Infrared-thermometer

- Uses thermal radiation. 

- A hotter object emits more thermal radiation. 

- The tympanic (ear) thermometer measures temperature this way.

Temperature sensitivity

Oventhermometer 

       - not very accurate

Clinical thermometer 

       - half a degree is important.

Liquid thermometer 

       - How much liquid rises with an 

           increase of 1 degrees celsius

Increase sensitivity:

... of a liquid thermometer

- Use a larger reservoir of liquid

- Use a thinner tube

Expansion and contraction in solids:

- Temperature increase - expansion

- Temperature decrease - contraction

Architects and design engineers

of bridges and train tracks must

allow for this expansion and contraction

Netherlands

The difference between the highest and lowest temperature is about  50 degrees celsius. A steel beam 20m long gets 1,2 cm longer with this temperature increase.

Bimetal strip:

This is a strip made up of two layers of differnt metals. Both metls expand differently, which means that 

the strip bends when the temperature changes.

Application:

- Thermometers

- Electric ovens, irons and coffee makers (because these have switches that switch off at a certain temperature).

The Celsius temperature scale is based on boiling water and melting ice.

1. True
2. False

-273 degrees celsius = 0 K

1. True
2. False

The absolute zero is at 0 K

1. True
2. False

An ear thermometer works with the expansion of a solid material

1. True
2. False

Solids contract with increasing temperature

1. True
2. False

Questions

45 up to 51