In transmission of power from generation plants to users, transformer…

The correct answer is Option (1) → (A) and (C) only

For a given power \( P = VI \), a higher voltage means a smaller current, and the power lost as joule heating in the line wires of resistance \( R \) is \( I^{2}R \).

    \( \displaystyle P_{\mathrm{loss}} = I^{2}R = \left(\frac{P}{V}\right)^{2} R \)

So power is sent at high voltage: a step-up transformer at the plant, and step-down transformers near the users.

(A) A step-up transformer is used at the generation plant and high voltages are transmitted. — Correct. Raising the voltage at the plant is what keeps the line current small.

(B) A step-down transformer is used at the generation plant and low voltages are transmitted. — Incorrect. Low-voltage transmission would need a large current and would waste much power in the lines.

(C) A step-up transformer lowers the current and hence loss due to joule heating is less. — Correct. In a transformer \( V_s I_s \approx V_p I_p \), so raising the voltage lowers the current, and the loss \( I^{2}R \) falls.

(D) A step-down transformer lowers the current and hence loss due to joule heating is less. — Incorrect. A step-down transformer lowers the voltage and raises the current, which would increase the loss.

NCERT (2026-27):
Transformers – “… The large scale transmission and distribution of electrical energy over long distances is done with the use of transformers. The voltage output of the generator is stepped-up (so that current is reduced and consequently, the I²R loss is cut down).”