Question

An air-cored transformer is assumed to be 100% efficient. The ratio of the secondary turns to the primary turns is 1:20. A 240V ac supply is connected to the primary coil and a
6Ω
load is connected to the secondary coil. what is the current in the primary coil?

Answer 1

Answer on Question #45720, Physics, Electromagnetism

An air-cored transformer is assumed to be 100 % efficient. The ratio of the secondary turns to the primary turns is 1:20. A 240V ac supply is connected to the primary coil and a 6 $\Omega$ load is connected to the secondary coil. what is the current in the primary coil? Solution

100 % efficiency means that transformer will save power. Hence

$\frac{U_{1}}{U_{2}}=\frac{I_{2}}{I_{1}}=\frac{N_{1}}{N_{2}}=\frac{20}{1}$

If in primary coil there is 240 V, in secondary it will be

$U_{2}=\frac{U_{1}}{20}=240/20=12\,V$

Then current in secondary coil is

$I_{2}=\frac{U_{2}}{R}=\frac{12}{6}=2\,A$

So now we can find current is primary coil

$I_{1}=20I_{2}=20\cdot 2=40\,A$

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