# I The circuit of the induction coil

1. Dec 20, 2017

### Aya Elsayed

When we turn the circuit off . There will be an induced emf through the coil due to the changing magnetic field of the AC . Therefore V=-L . DI/Dt
So when the current is zero then the emf has a maximum value . And what about the emf of the source itself ? It's equal to the induced emf? If It has the same value and an opposite direction whey they don't cancel each other out ?

2. Dec 20, 2017

### kuruman

What circuit? Can you be more specific and describe it, even better can you post it as a figure?

3. Dec 21, 2017

### Aya Elsayed

4. Dec 21, 2017

### kuruman

OK, I see. The voltmeter cannot detect an instantaneous voltage, which is what you are talking about. You will get a better picture of the instantaneous voltage if you connect an oscilloscope across the induction coil.

5. Dec 21, 2017

### Aya Elsayed

I got it ... So It only detects the voltage between the coil .
So what I said about the sum of the voltages is right ?

6. Dec 21, 2017

### kuruman

According to the Kirchhoff rule, the sum of the voltages around the closed circuit is zero at any time. That is always the case.