Chapter 4 Notes

Temperature- how hot or cold something is.

Note- As we move through this unit we will discover a more scientific definition for temperature!

Temperature of Various Familiar Objects

Human body temperature- 37˚C

Boiling water- 100˚C

Freezing water- 0˚C

Comfortable room temperature- 20-25˚C

Fridge- 3-5˚C

Freezer- -18°C

Absolute Zero (coldest temperature possible)- -273°C OR 0 K

Measuring Temperature

Technologies used in the past:

Galileo’s air thermometer

Also called the thermoscope.

Detects changes in temperature but does not have an accurate scale.

Showed whether air was hot or cold.

Liquid moves up as air cools and down as it (the air) warms up

Early liquid thermometers

Also called liquid thermoscopes.

Liquid expands when heated and contracts when cooled.

Liquid raises as it warms and lowers as it cools

Liquids used- mercury and alcohol.

The difference between a thermoscope and a thermometer is that thermoscopes DO NOT have a scale on them.

Scales used to measure temperature:

Celsius (˚C)

The most common scale for measuring temperature. On this scale, water at sea level boils at 100°C and freezes at 0°C. Developed by Anders Celsius.

Fahrenheit

The first widely used temperature scale. On this scale, water at sea level boils at 212°F and freezes at 32°F. Developed by Daniel Gabriel Fahrenheit.

Kelvin

A scale used for measuring temperatures in scientific experiments. On this scale, pure water freezes at 273 K and boils at 373 K; the coldest possible temperature (also known as absolute zero) is 0 K. Developed by Lord Kelvin.

Our bodies are very temperature sensitive!

Hyperthermia- rise in internal body temperature

Hypothermia- drop in internal body temperature

Both of these can result in: hallucinations, damage to body tissues (including the brain), serious illness and even death.

Temperature measuring devices:

Liquid Thermometer

The most common temperature measuring device. Typically marked with either Celsius and/or Fahrenheit degree scales.

Is a liquid thermoscope except that it has a scale.

Resistance Thermometer

Also known as a digital thermometer.

Uses electrical resistance to determine temperature.

Bimetallic strip

A metal strip where there are two different metals bonded back to back.

This strip bends and coils in a certain direction depending on if it is heated or cooled.

This is due to the metals expanding at different rates when heated.

Thermostat

Switches on and off to keep a room at a preset temperature.

Functions through the use of a bimetallic coil.

Thermocouple

This uses electricity to measure temperature.

There are two different metal wires attached at two different ends.

If the two ends are at different temperatures then a current flows between the two and can be measured in terms of temperature.

Used for places where people cannot go (inside computers, smokestacks, volcanoes, etc.)

Infrared Thermometer

Measures the amount of heat an object emits by using light in the infrared spectrum.

Coloured images called thermograms are used to show the data collected by this thermometer

Hot objects appear as bright colours (red, yellow, white, etc.) while cool objects appear as dark colours (blue, black, etc.).

Commonly used for things such as search and rescue.