Question

Why is AC preferred over DC for transmission of electrical power:
A. AC to DC conversion and vice versa is easy
B. transmission losses in AC are lower
C. AC transmission is unaffected by random phase change
D. Frequency of AC does not change.

Answer 1

We know that current is of two types depending on how they flow, namely alternating current or AC and direct current or DC. Both have their own advantages and disadvantages. Clearly, AC is affected by phase and hence C is not the answer.

Complete step by step answer:
We know that in DC, the current flows only in one direction and it is easy to store such currents.
Similarly, in AC, the direction of the current changes for each cycle. The frequency of the AC circuit is maintained constant within countries only. But here the option D says frequency of AC does not change, which is not true and thus D is not the answer.
From the given question it is clear that AC is preferred instead of DC for transmission.
The reasons are, it is easy to convert AC to DC only. But here the option says AC to DC conversion and vice versa is easy which is wrong. Hence A is not the answer.
Clearly, option A, C, and D are ruled out leaving behind option B. Let us check option B also.
Leaving transmission losses in AC are lower. This is true as transmission loss is given by $I^{2}R$ and we know that $V=IR$, then loss$=\dfrac{V^{2}}{R}$, if the current is DC then large $R$ is needed to maintain less loss. But the $R$has limitations with respect to lengths and thickness. But AC can be stepped down using a transformer and later stepped up when needed
Hence the answer is B. transmission losses in AC are lower.

Note:
AC is preferred for transmission as it is easy to step up or down, can be converted to DC easily and can be disturbed easily to households. Also, the frequency of AC in India is $50-60Hz$ i.e. the current changes its direction $100$ times per second. Note that transmission loss is given by $I^{2}R$.