(a) State two properties of glass which makes it a particularly suitable material to use in the construction of a mercury-in-glass thermometer.
(b) Contrary to popular opinion, mercury expands only a small amount when it is heated; there are many liquids which expand a great deal more. State two reasons why mercury is still often used in thermometers.
(c) A resistance thermometer is placed in a bath of liquid at 0 °C and its resistance is found to be 3740 Ω. At 100 °C, its resistance is 210 Ω. The bath is now cooled until the resistance of the thermometer is 940 Ω.
(i) What is the temperature of the bath, as measured using the resistance thermometer?
(ii) The reading taken at the same time on a mercury-in-glass thermometer placed in the bath is 40 °C. Suggest a reason for the difference between this reading and the value calculated in (c) (i).
Answer:
(a) Glass is transparent. This allows for easy reading of the mercury column in the thermometer.
Glass also has a very high melting point, one which is higher than the maximum temperature a mercury-in-glass would measure.
(b) Mercury has a high boiling point and low freezing point.
Mercury is opaque.
Mercury expands uniformly with temperature.
[Any 2]
(c)
(i)
= 79.3 °C
(ii) Different thermometric properties vary differently with temperature.
