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Question
A step-down transformer connected to the main supply of 220 V is used to operate 11V,88W lamp. Calculate
- Voltage transformation ratio and
- Current in the primary
Solution
Given data:
Vp = 220 V, Ps = 88 W, Vs = 11 V
Transformation ratio K = `"V"_"s"/"V"_"p"`
K = `11/220 = 1/20 = 1 : 20 = 1/20`
Current in the primary Ip = ?
`"P"_"S" = "V"_"S" "I"_"S"`
`"I"_"S" = "P"_"S"/"V"_"S" = 88/11` = 8 A
`therefore "I"_"p"/"I"_"S" = "K"`
`"I"_"p" = "KI"_"S"`
`therefore "I"_"p" = 1/20 xx 8 = 2/5 = 0.4`
Ip = 0.4 A
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