Question

The higher and lower fixed points on a thermometer are separated by 150 mm. When the length of the mercury thread above the lower temperature is 30 mm, the temperature reading would be

• A. ${25}^{\circ }C$
• B. ${30}^{\circ }C$
• C. ${10}^{\circ }C$
• D. $0^{\circ }C$

Answer 1

Answer: (A)

${25}^{\circ }C$

The thermometer has upper fixed point (UFP) at $150mm$ and let the lower fixed point be at $0mm$ thus the distance of separation is maintained of $150mm$.

New fixed point(P) is $30mm$ thus we can find the temperature by using the formula of $\frac{(P-LFP)}{(UFP-LFP)}=\frac{C}{100}$ (where $C$ is the temperature).

$\frac{(30-0)}{(150-0)}=\frac{C}{100}$.

$\frac{30}{150}=\frac{C}{100}$.

$\frac{1}{5}=\frac{C}{100}$.

Hence, $C={25}^{0}C$,