Electrical energy is transmitted over long distances at high alternating voltages by the use of a transformer. Choose the correct statements from the following:
(A) Higher voltage implies less power loss.
(B) The alternating magnetic flux induces eddy currents in the iron core and causes heating.
(C) Step up transformer increases the current by reducing the voltage in the above transformer.
(D) Transmission lines can be made thinner to reduce power loss.
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → (A) and (B) only
A transformer changes an alternating voltage by mutual induction between two coils on one iron core. For a fixed power \( P = VI \), a higher transmission voltage means a smaller current, and the power lost as heat in the line of resistance \( R \) is
\( \displaystyle P_{\mathrm{loss}} = I^{2}R = \frac{P^{2}R}{V^{2}} \)
(A) Higher voltage implies less power loss. — Correct. For the same power, a higher voltage carries a smaller current, and the loss \( I^{2}R \) falls as \( 1/V^{2} \).
(B) The alternating magnetic flux induces eddy currents in the iron core and causes heating. — Correct. The changing flux induces eddy currents in the solid iron, and these heat the core; laminating the core keeps them small.
(C) Step up transformer increases the current by reducing the voltage in the above transformer. — Incorrect. A step-up transformer raises the voltage and lowers the current; this is the very reason it is used at the power station.
(D) Transmission lines can be made thinner to reduce power loss. — Incorrect. A thinner wire has a larger resistance \( R = \rho l/A \), so the loss \( I^{2}R \) increases.
NCERT (2026-27):
Transformers – “… (iii) Eddy currents: The alternating magnetic flux induces eddy currents in the iron core and causes heating. The effect is reduced by using a laminated core.”
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).”