The ends of an element of zinc wire are kept at a small temperature difference $\Delta T$ and a small current $(I)$ is passed through the wire. Then, the heat developed per unit time

• Correct answer
  A

  is proportional to $\Delta T$ and /
• B

  is proportional to $I^3$ and $\Delta T$
• C

  is proportional to Thomson coefficient of the metal
• D

  is proportional to $\Delta T$ only

Hence, the correct answer is option: 'A'.