The resistance of a platinum resistance thermometer is 30 ohms at the ice point, 40 ohms at the steam point and 34.5 ohms on a certain hot day, what is the temperature of the day on celcius temperature day?

1 answer

at T = 0, R = 30
at T = 100, R = 40

if we assume linear behavior
T = m R + b

m = change in T/change in R = 100/40
= 2.5
so
T = 2.5 R + b
when T = 0, R = 30 so
0 = 2.5*30 + b
b = - 75
so
T = 2.5 R - 75
if R = 34.5 then
T = 2.5(34.5) - 75
T = 11.25 degrees C