For a thermocouple, the neutral temperature is \[{270^0}C\]and the temperature of its cold junction is \[{20^0}C\]. If there is no deflection in the galvanometer, the find the temperature of the hot junction.
A. \[{210^0}C\]
B. \[{540^0}C\]
C. \[{520^0}C\]
D. \[{209^0}C\]

Hint: Before we start addressing the problem, we need to know about the thermocouple. A thermocouple works on the principle of the seebeck effect. A thermocouple is an instrument that acts as a sensor that is used to measure the temperature. Basically, this consists of two dissimilar wires, in which one wire is connected to the sensor and the other wire is connected to the thermometer in order to obtain temperature. Here, they have given the value of neutral temperature and the temperature of the cold junction so we have to find the temperature of the hot junction when there is no deflection in the galvanometer.

Formula Used:
The formula to find the temperature of the hot junction is given by,
\[{T_n} = \dfrac{{{T_C} + {T_h}}}{2}\]……… (1)
Where,
\[{T_n}\] is neutral temperature.
\[{T_C}\] is the temperature of a cold junction.
\[{T_h}\] is the temperature of a hot junction.

Complete step by step solution:
In the question, they have given the neutral temperature and temperature of cold.
\[{T_n} = {270^0}C\]and \[{T_C} = {20^0}C\]
To calculate the temperature of the hot junction the formula for is given by,
\[{T_n} = \dfrac{{{T_C} + {T_h}}}{2}\]
\[ \Rightarrow {T_h} = 2{T_n} - {T_C}\]
Now, substitute the values of \[{T_C}\]and \[{T_n}\]we get,
\[ \Rightarrow {T_h} = \left( {2 \times 270} \right) - 20\]
\[ \therefore {T_h} = {520^0}C\]
Therefore, temperature of the hot junction is \[{520^0}C\].

Hence, option C is the correct answer.

Note:If the temperature of the hot junction is increased, and the cold junction is kept at 0o C, the galvanometer deflection will increase which means that the emf also increases till it becomes maximum called as neutral temperature.