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A step down transformer works on 220 V a mains. What is the efficiency of the transformer when a bulb of 100 W, 20 V is connected to the a mains and the current in the primary is 0.5 A ?

Answer»

Data: Vp = 220V, Vs = 20V, Ps = 100W, Ip = 0.5 A

The Input power. Pp = IpVp = (0.5)220) = 110 W

The output power, Ps = 100 W

∴ The efficiency of the transformer

\(\cfrac{output \,power}{input \,power}\) = \(\cfrac{100}{110}\) = 0.9091 or 90.91%



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