Temperature and heat

Question 1

Temperature

Answer 1

The measure of the hotness or coldness of a body.

Question 2

Thermometric property

Answer 2

The physical property of a thermometer that changes measurably with temperature.

Question 3

Length of a column of mercury

Answer 3

• A glass tube with a very narrow bore is sealed at both ends.
• One end is enlarged and contains mercury. This is the mercury reservoir.
• If this end is placed in warm water the mercury expands and this causes the mercury to rise up the tube.
• The length of the column of mercury is determined by the temperature of the water.

Question 4

Emf of a thermocouple

Answer 4

• Two wires made up of different metals (copper and constantan) are joined at both ends.
• If the ends are at different temperatures, an emf (Seebeck emf) is generated.
• The size of the emf depends on the temperature difference between the ends of the wire.
• The size of the emf can be used to measure temperature.

Question 5

Resistance of a wire

Answer 5

• As the temperature of a wire increase so does the resistance of the wire.
• Since resistance depends on temperature, resistance can be used to measure temperature.

Question 6

Colour of liquid crystals

Answer 6

Temperature changes can affect the colour of a liquid crystal, which makes them useful for temperature measurement.
For example, if a black thermometer is placed onto someone’s forehead it will change colour depending on the temperature of the person.

Question 7

A gas

Answer 7

• The pressure of a fixed mass of gas at a constant volume is the thermometric property of the constant volume gas thermometer.
• The volume of a fixed mass of gas at constant pressure is another thermometric property involving a gas.

Question 8

To calibrate a liquid-in-glass thermometer

Answer 8

• A half-metre stick is attached to a hollow glass tube which contains a coloured liquid.
• This is placed in a beaker of melting ice at 0°C.
• The temperature of the ice is measured with a mercury thermometer, i.e the mercury thermometer is used as the standard thermometer

Question 9

To calibrate a liquid-in-glass thermometer, data

Answer 9

• Note and record the temperature of the ice and the length of the coloured liquid in the glass tube.
• By slowly heating the arrangement note and record both temperature and the length of liquid at a range of different temperatures, 10°C, 20°C……

Question 10

To calibrate a liquid-in-glass thermometer - accuracy

Answer 10

• The use of a stirrer ensures that the water in the beaker has a uniform temperature.
• Avoid in the error of parallax when using the half metre stick to measure the length of the liquid in the glass tube.
• Make sure the half metre stick stays firmly attached to the glass tube for the duration of the experiment.

Question 11

To use the newly calibrated liquid-in-glass thermometer,

Answer 11

• Place the glass tube and half metre stick in the substance whose temperature is required.
• Note the length of the liquid column.
• Draw a horizontal line from this length value on the y-axis to the straight line graph.
• Draw a vertical line to the x-axis and note the temperature value.

Question 12

To calibrate a thermocouple thermometer

Answer 12

• A copper constantan thermocouple is arranged with the hot junction in the test tube of oil and the cold junction (reference junction) in melting ice.
• A Bunsen burner heats the water bath which heats the oil in the test tube which in turn heats the hot junction.
• The temperature of the oil and hot junction is recorded with a mercury thermometer, i.e laboratory mercury thermometer is used as the standard thermometer.

Question 13

To calibrate a thermocouple thermometer - data

Answer 13

Note and record the temperature of the hot junction (0°C, 10°C, 20°C….) and the corresponding values of emf as indicated by the millivoltmeter.

Question 14

To calibrate a thermocouple thermometer - accuracy

Answer 14

• The use of a stirrer ensures that the oil has a uniform temperature. Thus the temperature of the oil is the temperature of the hot junction.
• Heat the oil slowly to further ensure the temperature of the oil is the temperature of the hot junction.
• Check and correct if necessary any zero error on the millivoltmeter.

Question 15

To use the newly calibrated thermocouple thermometer

Answer 15

• The hot junction is placed in the substance whose temperature is required and the emf is noted.
• The reference junction must be kept in the melting ice.
• Draw a horizontal line from the emf value on the y-axis to the straight line graph.
• Draw a vertical line to the x-axis and note the temperature.

Question 16

Clinical thermometer

Answer 16

• The constriction is designed to stop the liquid falling back into the reservoir when the thermometer is taken from the patient’s mouth.
• This allows for an accurate value of temperature to be recorded.
• The thermometer is shaken before being used again to force the liquid back into the reservoir.

Question 17

Oven / boiler thermometer

Answer 17

• A thermocouple thermometer could be used to measure the temperature inside an oven or boiler.
• The emf generated would be translated to a temperature reading.

Question 18

Will the temperature read on a thermocouple thermometer and a liquid-in-glass thermometer be the same?

Answer 18

Probs not