Electrical energy is transmitted over large distances at high alternating voltages. Which of the following statements is (are) correct?


Option(a):


In an ac circuit power is given by:



where Vrms is the rms voltage and Irms is the rms current and



Now, ϕ is constant for a particular ac connection. If Power is constant, rms current and rms voltage have an inverse relation. Thus, higher voltage means lower current. Thus, this option is correct.


Option(b):


We have established that we get a lower current. Now, the power dissipated (not the net power supplied by the source) through the transmission wires of resistance R is given by:



As I is lower, Pdissipated is also less. Hence, this option is correct.


Option(c):


Making the transmission lines thinner is not a good idea. As resistance is inversely proportional to area, the resistance will increase. Hence energy dissipated will also increase( ). Thus, this is incorrect.


Option (d):


This is true. We can use transformers to increase or decrease voltages and decrease or increase current respectively. This is correct.

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