CAIE IGCSE Physics Ideal Transformer IpVp = IsVs

Practise applying equal input and output power in a 100%-efficient transformer to calculate primary or secondary current from paired voltage values.

Exam points

apply I_pV_p = I_sV_s because input power equals output power at 100% efficiency
rearrange the equation to calculate an unknown primary or secondary current with consistent units
combine a lamp rating, fuse limit or turns-ratio result with power conservation in multi-step problems

[Maximum number: 2]

Fig. 10.1 shows a transformer that consists of two coils P and Q, and an iron core.

Fig. 10.1

There are 200 turns on coil P and 340 turns on coil Q.

A4.0 V a.c. power supply is connected to coil P.

A heater is connected to coil Q. The current in the heater is 3.5 A. The transformer is 100% efficient.

Calculate the current in coil P.

current =

$\left(I_{P}=\right) I_{S} V_{S} / V_{P}$ OR $3.5 \times 6.8 \div 4.0$

C1

6.0 A

A1

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