A platinum resistance thermometer wire has a resistance of 70hms at 0°Cand 7.5 Ohms at 100°C. Calculate the temperature of the wire when the resistance is 7.2 Ohms

A. 15°C
B. 40°C
C. 20°C
D. 10°C

Correct Answer:

Option B – 40°C

Explanation

R0 = 7Ω , R1 = 7.2 Ω, R2 = 7.5 Ω, Tx = ?

[(X – T100°C) ÷ (R1 – R0)] = [(T100°C – T0°C) ÷ (R2 – R0)]

[(Tx – 0) ÷ (72 – 7)] = [(100 – 0) ÷ (7.5 – 7)]

Tx/0.2 = (100 ÷ 0.5)

Tx = [(0.2 × 100)] ÷ 0.5

= 20/0.5 = 40°C