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Question
The primary of a transformer has 40 turns and works on 100 V and 100 W. Find a number of turns in the secondary to step up the voltage to 400 V. Also calculate the current in the secondary and primary.
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Solution
Given:
NP = 40, eP = 100 V, PP = 100 watt, eS = 400 V
To find:
- Number of turns in the secondary (NS)
- Current in the secondary (IS)
- Current in the primary (IP)
Formulae:
- `"e"_"p"/"e"_"s" = "N"_"p"/"N"_"s"`
- P = Ie
Calculation:
From formula (i),
`"N"_"s" = "N"_"p" xx "e"_"s"/"e"_"p" = (40 xx 400)/100`
∴ NS = 160
For an ideal transformer, PS = PP
From formula (ii),
PS = ISeS
∴ IPeP = ISeS
∴ Is = `("I"_"p""e"_"p")/"e"_"s"`
= `"P"_"p"/"e"_"s" = 100/400 = 0.25` A
Ip = `"P"_"p"/"e"_"p"`
Ip = `100/100 = 1` A
∴ Ip = 1 A
- The number of turns in the secondary is 160.
- The current in the secondary is 0.25 A.
- The current in the primary is 1 A.
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