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I have to measure the current and voltage of a coil with an oscilloscope.

In this case, does P Watt = Irms*Vrms?

The induction cooker writes that the maximum Watts is 1.2K, but I measure it over 1.2 kW.

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    \$\begingroup\$ PLEASE DON'T SHOUT. Why do you need to use an oscilloscope? \$\endgroup\$ – pipe Sep 12 '18 at 12:28
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Oscilloscope can only look at voltage. If you need to look at current, then you need a current probe, which turns current into a voltage signal that you can look at.

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The average power is the definite integral over the time period in question (one or more integral cycles would be good here) of v(t)*i(t). That’s energy - divide by the time interval to yield power.

Vrms * Irms is the apparent power, which is always greater than (or equal to) the real average power.

If the load is completely resistive then the current is in phase with the voltage and the two are equal. If the load is completely reactive (like a capacitance or inductance) no power is transferred (ideally) because the current is 90° out of phase with the voltage, but the voltage and current are both non-zero.

Many oscilloscopes have math functions that can do this calculation if you can read v(t) and i(t) on different channels. Your 'scope manual would be the place to look.

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