Practice portal › Alternating Current › AC Generator and Transformer

For an ideal step-down transformer,

Asked in GSEB Board July 2021 · Transformers

(1) V_S<V_P and I_S<I_P
(2) V_S>V_P and I_S>I_P
(3) V_S>V_P and I_S<I_P
(4) V_S<V_P and I_S>I_P

Answer: (4) V_S<V_P and I_S>I_P

Step-by-step solution

Idea: a step-down transformer has fewer turns in the secondary, N_S<N_P.

Voltage ratio: (V_S)/(V_P)=(N_S)/(N_P)<1, so V_S<V_P.

Ideal transformer: no power is lost, V_SI_S=V_PI_P, so (I_S)/(I_P)=(V_P)/(V_S)>1.

So V_S<V_P and I_S>I_P.

Why the other options are wrong

(1) Voltage and current cannot both fall. For an ideal transformer V_SI_S=V_PI_P, so if the voltage is stepped down the current must be stepped up.
(2) Both rising would make the output power larger than the input, creating energy. Besides, a step-down transformer has V_S<V_P by definition.
(3) This describes a step-up transformer, with more turns in the secondary than in the primary.

More AC Generator and Transformer questions

All AC Generator and Transformer questions →

Reading this solution needs no sign-in. You only sign in to practise against the clock and keep your progress.

Practise this with a timer