Step-up vs step-down — what changes on the secondary? For a step-up transformer (higher secondary voltage than primary), indicate what quantity increases at the secondary side in an ideal transformer.

Introduction / Context:
Transformers trade voltage and current while conserving power (ideally). A step-up transformer produces a higher voltage at the secondary than at the primary, which has practical applications in power distribution and certain electronics.

Given Data / Assumptions:

• Ideal transformer (no copper losses, no core losses, no leakage).
• Turns ratio a = Np/Ns < 1 for a step-up (Ns > Np).
• Power balance approximates to Vp * Ip ≈ Vs * Is (ideal).

Concept / Approach:
Voltage ratio equals turns ratio: Vs/Vp = Ns/Np. For a step-up transformer, Ns > Np, so Vs > Vp. To keep power roughly constant, current goes the other way: Is < Ip. Power does not increase; transformers do not create power, they only transform it.

Step-by-Step Solution:

Verification / Alternative check:
Example: Np = 100, Ns = 1000. If Vp = 12 V, Vs ≈ 120 V (voltage up), while current scales down by 10x.

Why Other Options Are Wrong:
Increase the current: False; current decreases when voltage steps up.

Increase the power: Power is not increased by an ideal transformer; it is transferred with losses only.

Decrease the voltage: Opposite of a step-up function.

Common Pitfalls:
Assuming transformers “boost power.” Forgetting that higher voltage implies lower current for similar power transfer.

Final Answer:
increase the voltage