Question

When a thermometer is taken from the melting ice to warm liquid, the mercury level rises to \[{\left( {\dfrac{2}{5}} \right)^{th}}\] of the distance between the lower and the upper fixed points. The temperature of liquid in K is
A.217.15
B.313.15
C.220
D.330

Answer 1

Hint: Thermometry is the branch of physics which deals with the measurement of temperature. In this question we have to find the temperature of liquid in Kelvin so we will use the Kelvin temperature scale. The lower fixed point of Kelvin scale is at 273.15K and the upper fixed point is at 373.15K

Complete step by step solution
The lower fixed point of the Kelvin scale is at 273.15K and the upper fixed point is at 373.15K so the distance between lower fixed point and the upper fixed point is 100K. Now in the question it is given that the thermometer is taken from melting ice to warm liquid so, when the thermometer is in melting ice the mercury level will be at lower fixed point i.e. at 273.15K and when it is placed in warm liquid the mercury level rises to \[{\left( {\dfrac{2}{5}} \right)^{th}}\] of the distance between lower and upper fixed point so, the height of mercury will be \[\dfrac{2}{5} \times 100K\] i.e. 40K and the reading will be given as the reading at lower fixed point plus the height of mercury column i.e. \[273K + 40K\] which is equal to 313.15K. Hence the correct option will be B.

NOTE: The temperature of the liquid column cannot be directly given by the height of the mercury column because the lower fixed point in the Kelvin scale is at 273.15K so the reading will be given by adding the lower fixed point to the height of mercury column.