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I have studied that the nichrome, which has high resistance, is used in heat coils to increase the heat released. But according to this equation, $$H=\frac{V^2}{R} t,$$ heat is inversely proportional to resistance. How does it increase the heat released in heat coils? And then what is the use of using high resistance metals for heat producing?

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  • $\begingroup$ the $T$ stands for time ($t$) and not temperature. Please use correct notation. Returning to the question, one has to use the equation $H = i^2 R t$, where $i$ is the current flowing through the resistor. Resistance is the impedance to the flow of current which gives rise to heat. $\endgroup$ Nov 11, 2014 at 2:28
  • $\begingroup$ @Vaidyanathan: Ah, that makes more sense. OP wrote H=V2/R T, so I left capitalization alone. Note that if you do notice a mistake, you are able to hit the 'edit' button and correct it, rather than leaving an un-directed comment (i.e., ping someone using the Twitter-like @<name> capabilities here on SE) $\endgroup$
    – Kyle Kanos
    Nov 11, 2014 at 3:50
  • $\begingroup$ @KyleKanos Alright.. I did not know that :) $\endgroup$ Nov 11, 2014 at 15:07

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The power dissipated in a resistor is $I^2R=\frac {V^2}R$ It is true that for a given source voltage, the heat dissipated is inversely proportional to the resistance. You want the resistance of the heating coil to be high compared to the wiring that is supplying the current, as otherwise much of the power will be dissipated in the supply wiring instead of where you want. There should not be a factor $T$ in the heat dissipation. Nichrome does increase in resistance (as do most metals) with temperature, so for accuracy you should use the resistance at the operating temperature.

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