Question

The thermo emf of a thermocouple is given by $E\left(t\right)=40t-\frac{t^2}{20}$, where $t$ is the temperature of hot junction and the cold junction being kept at $0^{o}C$. What is the inversion temperature of the thermocouple ?

• A. ${400}^{o}C$
• B. ${1200}^{o}C$
• C. ${200}^{o}C$
• D. ${800}^{o}C$

Answer 1

Answer: (D)

${800}^{o}C$

The current in the wire is due to the drifting of electrons inside a wire in a direction opposite to the flow of electrons. During their drifting they collide with their atoms vibrating about their mean position and lose some of kinetic energy to the vibrating atoms which increases the amplitude of the vibration of the atoms thermal energy of the metal with the corresponding rise in temperature of the wire.
All wires which have electric current flowing through them have electrons moving through the wire. The reason for why wires heat up when a current flows through them is that a battery converts chemical energy into electric potential energy. This electric potential energy is given to the electrons, and since the electrons try to minimize their electric potential energy, the electrons convert this electric potential energy into kinetic energy. Due to the wires having electrical resistance, which means that they resist the motion of electrons, the electrons bump into atoms on the outside of the wire, and some of their kinetic energy is given to the atoms as thermal energy. This thermal energy is the wire heating up.