Measuring Temperature

Standard Temperatures

• Room Temperature: 22 oC

• Body Temperature: 37 oC

• Boiling Point of Water: 100 oC

• Freezing Point of Water: 0 oC

Standard Scales

• Scales are necessary for temperatures to be accurate and comparable.

• Three commonly used scales are:1.Fahrenheit (F)2.Celsius (C)3.Kelvin (K)

Comparing Scales

1.Fahrenheit (F)– Freezing of water occurs at 32 oF – Boiling of water occurs at 212 oF

2.Celsius (C)– Freezing of water occurs at 0oC – Boiling of water occurs at 100oC

3.Kelvin (K)– Scale states that the coldest temperature

possible –absolute zero (-273 ˚C)

How Thermometers Work

• Many thermometers work on the basis of expansion and contraction.

– Expansion: An increase in the volume of an object. Adding heat causes expansion.

– Contraction: A decrease in volume of an object. Occurs when heat is removed from an object.

Early Thermometers

– Galileo's Air Thermometer•As the air heats, the

liquids drops and rises when air is cooled.

• Early Liquid Thermometer:– Liquid rising up the

tube shows the temperature is rising.

Modern Liquid Thermometers

• Liquid thermometers use the expansion and contraction of liquids to measure temperature.

Clinical Themometer

• This type of thermometer is very sensitive to small changes in temperature but is able to measure temperatures only within a few degrees of normal body temperature.

Bimetallic Strip (Thermostat)

• Used to measure temperature in a room or appliance.

• They contain a strip made of two metals (bimetallic strip). The metals are different substances so when they are heated or cooled they will expand or contract by different amounts. The amount bending depends on the temperature.

Thermocouple

• Made of two wires of different metals.

• A temperature difference causes a current to flow through the wires. This current is measured by a meter.

• Can measure higher temperatures than typical thermometers.

Infrared Thermometer (Thermogram)

• Converts infrared radiation into colors that can interpret a temperature difference.

• Measuring Heat:

• http://app.discoveryeducation.ca/search?Ntt=measuring+temperature&N=18341&N=18342

Questions

1. Describe in your own words the main features of each device that measures temperature and where it is used.

2. How is a clinical thermometer different than a regular outdoor thermometer? Illustrate if necessary.

3. Describe how a thermostat keeps your home at a constant temperature.