Question

Why is AC used for long distance power transmission instead of DC?

• A. AC dissipates lower power than DC in a current carrying wire
• B. It is more convenient to step up/down voltage for AC than DC
• C. Power dissipation in AC is lower since frequency is high
• D. AC has lower risk of shock than DC

Answer 1

The correct option is B It is more convenient to step up/down voltage for AC than DC

Power wasted only depends on resistance and current in the circuit and does not depend on whether its AC or DC.
If P is the power transmitted, and R is the resistance of the line:
P=IV
Ploss = $I^{2}R=\frac{P^{2}R}{V^2}$
It is better to have lower current and higher voltage to reduce losses. AC is much easier (therefore cheaper) to step up and down in voltage(using a transformer) than DC, and can be done more efficiently than the much more expensive and complex DC step-up/step-down systems. That is why AC is used for power transmission.