Question

Why is electric power transmitted over long distances at high voltage?
A. To minimize power loss due to joule’s heating
B. To maximize power loss due to joule’s heating
C. To balance power loss due to joule’s heating
D. None of the above

Answer 1

Hint: We know that in a current flowing wire heat is produced because electrons collide with each other. The longer the wire, the more is the heat produced and more will be the resistance of the wire. Since power, voltage, and current are related to each other we have to adjust these to get the maximum benefit with minimum loss. So we will find the relation between power loss and voltage.

Complete step by step answer:
Copper aluminum or its alloys are used to make transmission lines. They are good conductors of electricity and heat. We know in conductors with an increase in temperature resistance increases as a number of collisions between electrons increases. The transmission lines go over very long distances hence they offer great resistance.

With the increase in resistance power loss increases. We know power loss is proportional to the square of the current flowing in the transmission line. If we decrease the current power loss will decrease. Hence voltage is to be increased to reduce current.Relation between power loss and current $I$ is given by,
$\text{Power loss} = {I^2}R$
Since, the power $P$ transmitted at voltage $V$ is
$P = VI$
$ \Rightarrow I = \dfrac{P}{V}$
Putting this in above we get the relation between voltage and power loss,
$\text{Power loss} = \dfrac{{{P^2}}}{{{V^2}}}R$
$ \therefore \text{Power loss} \propto \dfrac{1}{{{V^2}}}$

Hence option A is the correct answer.

Note: More reasons to transmit power at high voltage is that it reduces the cost of power transmission and improves its efficiency. Also to reduce power loss we cannot use superconductors that offer zero resistance because they need to be kept at low temperature, which won’t be convenient.