The resistance R of a piece of wire has thermometric properties which can be described as a linear function of temperature (T), see below: Where a and b are constants. The resistance of the wire is found to be 3.3 2 at the temperature of melting ice (0 °C) and 8.5 2 at the boiling of water (100 °C) at atmospheric pressure. [15 marks] a, find a and b b. determine the temperature when R is 6.9 2

R = a T + b (R is linear function of T, the temperature in kelvin)

At T = 273 K, R = 3.32

Put these values in the equation above '

3.32 = 273 a + b

At 100° = 373K, R = 8.52

8.52 = 373 a + b

8.52 - 3.32 = (373 - 273) a

a = 5.2 / 100 =.052

Putting this value of a in the first equation we get the value of b as follows

3.32 = 273 x. 052 + b

b = - 10.876.

So equation becomes

R =.052 T - 10.876

When R = 6.92, T = ?

6.92 =.052 T - 10.876

.052T = 17.796

T = 342.23K

T = 342.23 - 273 = 69.23 °C