Topic 2 Part 2 – Devices for measuring temperature

The Kelvin Scale After the creation of the Celsius scale, the Kelvin scale was created because new gases were being discovered. ◦ Scientists required a more accurate reading of high and low temperatures.

Absolute Zero Absolute zero is the coldest possible temperature ◦ Absolute zero on the Celsius scale is o C ◦ Absolute zero on the Kelvin scale is 0 K

What is the difference between heat and temperature Heat is a measure of energy of the particles moving around ◦ Thermal Energy is HEAT! Temperature is a measure of how hot or cold something is measured on a scale like a thermometer.

Different thermometers have been developed over time They suit different purposes:

How does a thermometer work? Explain in general how a thermometer works using the terms sensor, signal and responder. ◦ Page 199 Sensor: a material which responds to temperature change (ie: alcohol) Signal: Information about the temperature (ie: scale) Responder: A pointer, light or other mechanism that uses the signal (ie: level alcohol reaches)

Video: Eurika Science! Eurika! heat vs. temperature

Thermocouple Description ◦ - wires of two different metals are twisted together (copper and iron) ◦ - when heated it produces an electrical current Use ◦ - turn switch on or off it temperature changes Reason for Development ◦ - measures high temperatures ◦ - cannot be used to measure low temperatures

Bimetallic Strip Description ◦ - two metals fused together ◦ - expands at different rates ◦ - coils when heated - reverses when cools Use ◦ - operates electrical switches ◦ - controls furnace (thermostat), air conditioner, fridge Reason for Development ◦ - easy way to turn something on and off automatically

Recording Thermometer Description ◦ - a bimetallic strip joined to a lever with a pen Use ◦ - records small movement of temperature change ◦ - weather records Reason for Development ◦ - records temperature over a period of a week

Infrared Thermogram Description ◦ electronic sensor or device that photographs temperature change through colour ◦ photographs radiation Use ◦ detects air leaks ◦ energy efficient ◦ can be used to predict dangers of over heating Reason for Development ◦ detects precise temperature change - not visible to the eye ◦ quick and accurate

To measure temperature 1. Thermometer 2. Thermocouple 3. Bimetallic Strip 4. Recording Thermometer 5. Infrared Thermogram

Eurika Science! Eurika: Measuring Temperature

Thinking time! Which tool for measuring and controlling temperature would be most affective? 1. Controlling an electric frying pan? 2. Making long term records at the weather office? 3. Detecting small forest fires before they spread?

Controlling a fry pan  bimetallic strip

Long term records  Recording Thermometer

Forest Fire  Infrared Thermogram