# Current calculation

I have a question of confusion in my mind, so I thought to share it with you all. when we connect a halogen lamp of 12 VAC 50 watt to 220 VAC with the help of transformer, why the current consumption of light comes out as 0.22 Amp ?

My confusion is if we calculate the current with the secondary voltage ( 12 VAC ) of the transformer then the current consumption should be higher!

There is conservation of energy on both sides of the transformer. On the secondary side you're delivering 50W (12V @ 4.2A) so on the primary side you must supply 50W. 220VAC * .22A = ~50W.

Show your calculations if you want to figure out what you did wrong, but my guess your mistake stems from: 220V @ 50W = 0.22A. This is 0.22A at the 220V primary. At the 12VAC secondary, 50W = 4.17A. Since the power on the primary and secondary are equal (ignoring transformer loss),

$$V_{primary} I_{primary} = V_{secondary} I_{secondary}$$ so $$I_{secondary} = \frac{V_{primary} I_{primary}}{V_{secondary}}$$