Transformers

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A step-down transformer reduces a 2200 V primary supply and has 4400 turns on its primary winding. If the secondary is required to deliver 220 V to a load, how many turns must the secondary winding carry?

RankGuru · Accepted Answer

An ideal transformer transfers power between windings through a shared changing magnetic flux in the core, and the induced EMF in each winding is proportional to its number of turns, giving the turns relation $\dfrac{V_s}{V_p} = \dfrac{N_s}{N_p}$. Solving for the secondary turns, $N_s = N_p \times V_s/V_p$. Substituting $N_p = 4400$, $V_s = 220$ V and $V_p = 2200$ V gives $N_s = 4400 \times 220/2200 = 4400 \times 0.1 = 440$ turns. The option 880 doubles the correct ratio. The option 220 confuses the secondary voltage value with a turns count. The option 44000 inverts the ratio, which would describe a step-up transformer instead. This is the NCERT transformer relation that follows from Faraday's law applied to both coils sharing the same flux. A plausibility check confirms a step-down transformer must have fewer secondary turns than primary turns, and the tenfold voltage reduction matching a tenfold turns reduction is exactly self-consistent for an ideal lossless core.

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