# Numerical on resistance thermometer.

## A platinum resistance thermometer has a resistance of 2 ohm at 0° C and 3 ohm at 100° C. What will be the temperature when resistance indicates 5 ohm?

a. 300° C

b. 200° C

c. 350° C

d. 400° C

Correct Answer : a. 300° C

**Explanation :**

The resistance and temperature relation is given by *R = R*_{0 }(1 + αt) by electric resistance thermometer.

where *R*_{0 } is the resistance at 0° C

*R*_{0 } = 2 ohm

*R*_{100 } =3 ohm

= (1 + α 100)

Therefore α = 0.005

Now,

R= 5 ohm

5 = 2 (1 + 0.005t)

t = 300° C