(a) Distinguish between heat and temperature.
(b) State two physical properties of substances which may be used to measure temperature.
(c) State two reasons why mercury is preferred to alcohol as a thermometric liquid.
(d)(i) Describe how a mercury-in-glass thermometer is calibrated.
(ii) State two precautions necessary to ensure an accurate result.
(e) Explain how land and sea breezes occur.
(a) Heat is a form of energy that flows from a body at a higher temperature to one at a lower temperature; it is measured in joules. Temperature is the degree of hotness or coldness of a body, which determines the direction of heat flow; it is measured in kelvin (or degrees Celsius). Heat depends on mass, while temperature does not.
(b) Physical properties used to measure temperature:
- Expansion of a liquid (e.g. mercury) or of a solid.
- Variation of electrical resistance of a metal with temperature (also e.m.f. of a thermocouple, or pressure/volume of a gas).
(c) Why mercury is preferred to alcohol:
- Mercury has a high boiling point (about 357 C), so it can measure high temperatures without vaporising.
- Mercury is opaque and silvery, so it is easily seen, and it does not wet (stick to) glass, giving accurate readings; it also expands uniformly and conducts heat well.
(d)(i) Calibration. The bulb of the thermometer is placed in pure melting ice; when the mercury thread is steady its position is marked as the lower fixed point (0 C). The bulb is then placed in the steam above boiling water at normal atmospheric pressure and, when steady, that position is marked as the upper fixed point (100 C). The distance between the two marks is divided into 100 equal parts (degrees).
(d)(ii) Precautions:
- Use pure melting ice and pure water so the fixed points are correct.
- For the steam point, ensure standard atmospheric pressure and expose the bulb to steam, not the boiling water, and allow the thread to become steady before marking.
(e) Land and sea breezes. By day the land heats up faster than the sea, so the air over the land becomes warmer, rises, and is replaced by cooler air blowing in from the sea: this is the sea breeze. By night the land cools faster than the sea, so the air over the sea is now warmer and rises, and cooler air blows out from the land to the sea: this is the land breeze.
(a) Heat is a form of energy that flows from a body at a higher temperature to one at a lower temperature; it is measured in joules. Temperature is the degree of hotness or coldness of a body, which determines the direction of heat flow; it is measured in kelvin (or degrees Celsius). Heat depends on mass, while temperature does not.
(b) Physical properties used to measure temperature:
- Expansion of a liquid (e.g. mercury) or of a solid.
- Variation of electrical resistance of a metal with temperature (also e.m.f. of a thermocouple, or pressure/volume of a gas).
(c) Why mercury is preferred to alcohol:
- Mercury has a high boiling point (about 357 C), so it can measure high temperatures without vaporising.
- Mercury is opaque and silvery, so it is easily seen, and it does not wet (stick to) glass, giving accurate readings; it also expands uniformly and conducts heat well.
(d)(i) Calibration. The bulb of the thermometer is placed in pure melting ice; when the mercury thread is steady its position is marked as the lower fixed point (0 C). The bulb is then placed in the steam above boiling water at normal atmospheric pressure and, when steady, that position is marked as the upper fixed point (100 C). The distance between the two marks is divided into 100 equal parts (degrees).
(d)(ii) Precautions:
- Use pure melting ice and pure water so the fixed points are correct.
- For the steam point, ensure standard atmospheric pressure and expose the bulb to steam, not the boiling water, and allow the thread to become steady before marking.
(e) Land and sea breezes. By day the land heats up faster than the sea, so the air over the land becomes warmer, rises, and is replaced by cooler air blowing in from the sea: this is the sea breeze. By night the land cools faster than the sea, so the air over the sea is now warmer and rises, and cooler air blows out from the land to the sea: this is the land breeze.
