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Question

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

A
Transmission lines can be made thinner.
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B
Lower current implies less power loss.
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C
For a given power level, there is a lower current.
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D
It is easy to reduce the voltage at the receiving end using step-down transformers.
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Solution

The correct option is D It is easy to reduce the voltage at the receiving end using step-down transformers.
Formula used:

P=IrmsVrms cos(ϕ)

In an ac circuit power is given by:

P=IrmsVrms cos(ϕ)

cosϕ=RZ

where Vrms is the 𝑟𝑚𝑠 voltage and Irms is the 𝑟𝑚𝑠 current and ϕ is constant for a particular ac connection.

The power is to be transmitted over the large distances at high alternating voltages, so current flowing through the wires will be low because of given power (P). Hence, (a) option is correct.

Pdissipated=I2rmsR

As I is lower, Pdissipated is also less. Hence, (b) option is correct.

As resistance is inversely proportional to area, if area is decreased the resistance will increase. Hence energy dissipated will also increase
Pdissipated=I2rmsR
Thus, (c) is incorrect.

We can use transformers to increase or decrease voltages and decrease or increase current respectively. So, at the receiving end high voltage is reduced by using step-down transformers. Hence, (d) option is correct.

Final Answer: Option (a), (b), (d)

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