# A question on lenz law

1. Oct 6, 2012

### nik jain

1. The problem statement, all variables and given/known data

Figure shows two coils placed close to each other . When the key is pressed so that a current starts building up in one the coils

(a) a current flows along CBA in the loop

(b) a current flows along ABC in the loop

(c) No current flows through the loop

(d) An alternating current flows through the loop

3. The attempt at a solution

when the key is closed the current will flow from - terminal to + terminal of battery as a result increasing the flux through the other loop
Acc. to lenz law the current will flow along the abc in the loop .
but ans given is d . how???????

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2. Oct 6, 2012

### TSny

I agree with you that (b) is the best answer.

I assume you are just now getting to magnetic induction and Lenz's law. Technically, there will be a small, rapidly alternating current produced in each circuit due to the fact that the circuits would have a small amount of self-inductance and capacitance. But that's something you might cover later and I don't think that's what this question is about. Anyway, the question specifically asks for the induced current in the second loop when "a current starts building up" in the first coil. Even if you were to include self-inductance and capacitance, the answer would still be (b) when the current starts building up in the first coil.

3. Oct 6, 2012

### SammyS

Staff Emeritus
If you are using conventional current, then current flows from + the - terminal. Then Lenz's Law gives answer ABC.

If you are using electron current, then current flows from - the + terminal. Then Lenz's Law gives answer CBA.

4. Oct 6, 2012

### TSny

Yes, good catch! I overlooked nik jain's statement that the current would flow from - to + terminals.