Understanding Lenz Law: How Current Flows in Close Proximity Coils

[nik jain]

Homework Statement

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

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??

 

[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.

 

[SammyS]

Homework Statement

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

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??

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.

 

[TSny]

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.

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

 

[Nickie]

The answer is (d) An alternating current flows through the loop. This is because of the phenomenon known as electromagnetic induction, which is described by Faraday's Law. When the key is pressed, a changing magnetic field is created in the first coil, which then induces an alternating current in the second coil. This is due to the changing magnetic flux through the second coil, which results in an induced current. Lenz's Law states that the direction of this induced current will oppose the change in magnetic flux, hence causing an alternating current to flow in the opposite direction to the original current in the first coil. This is why the answer is (d) and not (b) as stated in the question.