Question

The higher and lower fixed points on a thermometer are separated by 160 mm. When the length of the mercury thread above the lower point is 40 mm, the temperature reading would be :

पर्याय

• 60°C

• 100°C

• 40°C

• 25°C

Answer 1

25°C

Explanation - 

Let the thermometer's upper fixed point (UFP) be 160 mm.

Set the thermometer's lower fixed point (LFP) to 0 mm to keep the separation distance at 160 mm. 

Fixed point of thermometer, P = 40 nm

${\displaystyle \left(\frac{\text{P}-\text{LFP}}{\text{UFP}-\text{LFP}}\right)=\frac{\text{C}}{100}}$

⇒ ${\displaystyle \frac{40-0}{160-0}=\frac{\text{C}}{100}\Rightarrow \frac{1}{4}=\frac{\text{C}}{100}\Rightarrow \text{C}=25°C}$