Temperature and Thermometers

1. Temperature and Thermometers Chapter 14

2. What is meant by the Temperature of a body? Temperature is a measure of the hotness or coldness of a body. What is the difference between heat and temperature? Heat is a Form of Energy. Temperature is a measure of the hotness or coldness of a body.

3. Internal Energy In a solid the molecules are bonded to each other and cannot move about freely. They can however vibrate. The higher the temperature the greater this vibration. The energy possessed by a body due to the Random Vibration of its molecules is called Internal Energy. The higher the Temperature of a body the greater the vibrational energy of its molecules is and hence the greater its internal energy.

4. What is the SI Unit of temperature? The SI Unit of temperature is the kelvin (K). What scale is the everyday practical scale of temperature? The Celsius Scale.

5. What is the relationship between the Celsius and the Kelvin Temperature Scales? Temperature in​ ​o​C    =  Temperature in kelvin  273.15 OR θ / o​C   =   T / K      273.15

6. What is a Thermometric Property? Any physical property that changes measurably with temperature is called a thermometric property. What is a Thermometer? A thermometer is an instrument used to measure temperature.

7. Thermometric Property and Thermometer Length of a column of liquid. When a liquid is heated it expands. If the liquid is in a thin capillary tube the length of the column of liquid increases as the temperature increases. This is the thermometric property on which the Mercury in Glass Thermometer and the alcohol thermometer depend.

8. Thermometric Property and Thermometer Resistance and the Resistance Thermometer Electrical resistance The electrical resistance of a conductor changes when the temperature does. The variation of this resistance with temperature can be measured. Resistance is the thermometric property on which the Resistance Thermometer is based.

9. Thermometric Property and Thermometer Emf and a Thermocouple If two different metals are joined together to form a circuit as shown and the two junctions maintained at different temperatures a small emf (a voltage) appears in the circuit. The emf can be measured with a voltmeter. The size of the emf varies with the temperature difference between the junctions. This device is called a Thermocouple and can be used to measure temperature.

10. Thermometric Property and Thermometer Colour Thermometers Colour The colour of certain crystals changes as the temperature does. This is the basis of one form of thermometer used to measure body temperature.

11. Thermometric Property and Thermometer Volume of a Gas at Constant Pressure. Gas Thermometer The diagram shows a gas syringe. It contains a fixed mass of gas and a rubber cap seals one end. Atmospheric pressure acts on the piston at the other end; thus the gas is at constant pressure. If the temperature of the gas is increased the volume of the gas increases and pushes the piston out. If the gas is cooled its volume decreases and the piston moves in. The volume of the gas at constant pressure is the thermometric property. This thermometric property is used in one type of gas thermometer.

12. Thermometric Property and Thermometer Pressure of a Gas at Constant Volume. Gas Thermometer A gas syringe can be used to show how the pressure of a fixed volume of gas varies with temperature. The syringe is set up as shown and the volume of the gas noted. The gas is then heated. To keep the volume at the same value weights will have to be placed on the end of the syringe. The larger the rise in temperature is, the greater the weights that must be added and thus the greater the pressure. The thermometric property is the pressure of a gas at constant volume.

13. Experiment to graduate a thermometer at the ice point and the steam point of water and use it to measure an unknown temperature in degrees Celsius. • Place an ungraduated alcohol thermometer in melting ice . • Mark the position of the top of the column of alcohol. • Measure the length (​L​ice​) of the column of alcohol. • This corresponds to zero degrees on the Celsius scale. • Place the thermometer in the steam above boiling water. • Mark and measure the length of the column (​L​steam​). • This corresponds to 100 degrees on the Celsius scale .

14. On graph paper plot the points (​ L​ice ​, 0) and (​ L​steam​, 100) as shown. Draw a straight line through these points. Place the thermometer at an unknown temperature θ, and measure the length of the column of alcohol ( L​θ). The unknown temperature can then be found from the graph.

15. Disagreement between Thermometers Two different thermometers, based on different thermometric properties, are graduated at the ice point and steam point of water and a Celsius scale created for each. Will the thermometers agree with each other when measuring temperature? Explain your answer. Why is it necessary to have a standard thermometer? What thermometer is usually used as a school laboratory standard? They will agree at 0​ ​o​C and 100​ ​o​C. In general they will not agree at other temperatures. They will not agree because different thermometric properties vary differently with changing temperature. Because different thermometers have different thermometric properties and give different readings at the same temperature. A mercury in glass thermometer.

16. To Plot the Calibration Curve of a Thermometer using the Laboratory Mercury Thermometer as a Standard.