The difference of temperature in a material can convert heat energy into electrical energy. To harvest the heat energy, the material should have

Solution

Physics sir · 4 steps

Keep the hot end hot and let the charges flow: block the heat, but pass the current.

1. What drives it. This is the thermoelectric (Seebeck) effect. A temperature difference across the material pushes charge carriers from the hot side to the cold side, and that creates a voltage. No temperature difference means no voltage.
2. Low thermal conductivity. If heat conducts through the material easily, the hot and cold ends quickly reach the same temperature. A poor heat conductor keeps that temperature difference alive, so the voltage keeps being produced.
3. High electrical conductivity. The voltage is only useful if it can drive a current. A good electrical conductor has low resistance, so less of the harvested energy is wasted as Joule heating I²R inside the material.

   ZT = (S² σ T)/κ

4. So. The figure of merit ZT of a thermoelectric material grows with electrical conductivity σ and falls with thermal conductivity κ. The material should have low thermal conductivity and high electrical conductivity, option (a).

The idea to keep. In a thermoelectric material the temperature difference is the fuel. Make it a poor conductor of heat so the difference survives, and a good conductor of electricity so the current flows with little loss.

Answer from the NTA final answer key. Solution by PrepWiser.