21. A typical thermometer uses a thin, cylindrical, glass tube with a large sphe

Question

21. A typical thermometer uses a thin, cylindrical, glass tube with a large spherical bulb at the bottom to hold mercury. Then, as the temperature rises, the mercury expands and is forced to rise up the cylindrical tube. Given the initial volume of mercury is approximately the volume of the spherical bulb (1cm3) and the cross sectional area of the tube is 3x10-4 cm2, how far will the mercury rise for a 5°C increase in temperature. The average coefficient of volume expansion for mercury is 1.8x10-4/°C and you can ignore the expansion of the glass.

Explanation / Answer

inital volume = 1 cm 3

increase in volume = 1.8x10-4/°C * 5 = 9x10-4 cm3

now this extra volume will will go into the tube.

the cross sectional area = 3x10-4 cm2

let the height be h

so volume in tube = A *h = 9x10-4 cm3

=> 3x10-4 * h = 9x10-4

=> h = 3 cm

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