# the thread of mercury in a thermometer is 17cm when placed above boiling water, and 9cm when dipped in melting ice. how long would the thread of mercury become if placed in a liquid with a temperature of 75 degree celsius.

is there a method or formula for this?

Yes there is a method. Assume a linear relationship. A temperature range of 100 C (from melting ice to boiling water) moves the mercury column 17-9 = 8 mm

A 75 degree temperature is 3/4 of the way from the 0 degree mark to the 100 degree mark. That is 6 cm past the 0 C mark, or 15 cm.

If you want to use an equation, let X = distance from the bottom of the "thread" of mercury

X = a T + b is the linear relationship.

a and b are constants you must determine.

When T = 0, X = 9, so b = 9

When T = 100, X = 17, so

17 = a*100 + 9

8 = 100 a

a = 0.08 cm per degree.

X = 9 + 0.08 T

When T = 75 C, X = 9 + (75*0.8) = 15 cm

okay... but i think i know another formular which is basically the same, but thanks anyway!