Question

$ - {40^0}F$ on absolute scale is equal to
A. $0{\text{ K}}$
B. ${\text{233 K}}$
C. ${\text{273 K}}$
D. ${\text{313 K}}$

Answer 1

Hint: Everybody has a certain temperature. There are various devices to measure the temperature of the body. Celsius, Fahrenheit and kelvin are the units of measurement of temperature and we have a formula to convert value in one unit to the other unit.

Formula used:
$\eqalign{
  & \dfrac{C}{5} = \dfrac{{F - 32}}{9} \cr
  & {T_K} = {T_C} + 273 \cr} $

Complete answer:
We got the value of temperature which is to be converted to another unit. Let us know how temperature is measured and what device is normally used to measure its working principle and then we will convert it into the required unit.
Generally when temperature difference is maintained then heat transfers from higher temperature body to the lower temperature body. The amount of heat transferred depends upon the various factors like the temperature difference, properties of material and amount of substance. That temperature is measured with a thermometer.
After transferring the heat, usually liquid will expand on heating. The main working principle of thermometers is this only.
When the thermometer is brought in contact with the body then the bulb which has mercury in it will get heated. The heat will be transferred to the mercury. When mercury gets heated it will expand in the thermometer and the readings which are calibrated on the thermometer will give us the temperature of the body.
If we have the temperature in Celsius scale then the temperature in Fahrenheit scale can be found out by formula
$\dfrac{C}{5} = \dfrac{{F - 32}}{9}$
We will convert the given Fahrenheit temperature to Celsius temperature and then to kelvin temperature.
Given temperature is ${40^0}C$ i.e 40 degree Celsius. So the temperature in Fahrenheit will be
$\dfrac{C}{5} = \dfrac{{F - 32}}{9}$
$\eqalign{
  & \Rightarrow \dfrac{C}{5} = \dfrac{{ - 40 - 32}}{9} \cr
  & \Rightarrow C = \dfrac{{ - 72}}{9} \times 5 \cr
  & \therefore C = - 40Celsius \cr} $
In kelvin scale we have the formula
${T_K} = {T_C} + 273$.
Where
${T_K}$ is the temperature in kelvin
${T_C}$ is the temperature in Celsius.
So in kelvin scale the temperature will be
${T_K} = {T_C} + 273$
$\eqalign{
  & \Rightarrow {T_K} = - 40 + 273 \cr
  & \therefore {T_K} = 233K \cr} $
So in kelvin scale the temperature will be 233 kelvin.

So, the correct answer is “Option B”.

Note:
Usually rather than using water as thermometer liquid we use mercury because the coefficient of thermal expansion of mercury is more than of water and hence we can get accurate readings with mercury even at small temperatures i.e range will be more for mercury.