Why does transmission always occur at high voltage?

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Hint: For understanding more on transmission and voltage affecting on transmission, it is essential to know about what power loss is. The loss in electric power flowing through the transmission line due to resistance is called ohmic loss. Explain the same using Joule’s law of heating.

Complete step by step answer:
Electric power is the measure of electrical energy transfer done by a circuit per unit time. Electric power is transmitted by transmission line from transformers and generators. Mathematically, electric power is given as the product of voltage across the line and the current passing through the line. Now, according to ohm’s law, the equation can be modified as,
\[P = VI\]
\[ \Rightarrow P = (I \times R)I\](According ohm’s law)

Since, we get a resistance factor, there is a slight droppage in power transmitted through the lines. The significant resistance can be due to the material and sometimes due to low current passing through the wire. Resistance is blockage offered to the flow of electrons but whereas it doesn’t affect the flow of charge. Hence, loss of power is not a function of voltage.
Now, according to Joule’s law of heating,
\[ \Rightarrow H = {I^2}RT\]

Heat produced on the line is directly proportional to the square of current passing through the circuit and the resistance. So, greater the heat flowing through the system, greater the resistance offered and hence, there is a power loss.

To minimize the power loss due to the resistance, the power transmission is node at higher voltage values so that the current is small and hence the power loss is small, owing to the resistance in the wire.

Note: Joule’s law of heating states that, when a current passes through a conductor having a resistance for a specified time period, then there will be heat developed on the conductor which can be given as the product of resistance, time and square of the current.