Induced Current (Magnetic)

[llama0lover]

Main Question or Discussion Point

A magnetic feild B, that is decreasing with time is directed out of the page and passes through a loop of wire in the plane of the page, as in my drawing (ignore that the dots are not evenly spaced, you can only do so much in paint) Which of the following is true of the induced current in the wire loop?

A) it is directed in to the page
B)it is directed out of the page
C) It is counterclockwise in direction
D) it is clockwise in direction
E) It is zero in magnitude

 

[llama0lover]

Okay, we got this problem now- thanks anyway, physics board!

 

[retracell]

Hey I'm having trouble with this problem too. What was the answer and how did you obtain it? Is it counterclockwise?

 

[kiwakwok]

According to the Lenz's law, an induced current flows in a direction that opposes the change causing it.

I think in this way:
As the out-of-paper magnetic field is decreasing in magnitude, the induced current should produce a magnetic field which minimizes the effect of such a change.
Therefore, a out-of-paper magnetic field should be generated.
Thus, the induced current should flow in a counterclockwise direction by the right-hand grip rule.

 

[retracell]

According to the Lenz's law, an induced current flows in a direction that opposes the change causing it.

I think in this way:
As the out-of-paper magnetic field is decreasing in magnitude, the induced current should produce a magnetic field which minimizes the effect of such a change.
Therefore, a out-of-paper magnetic field should be generated.
Thus, the induced current should flow in a counterclockwise direction by the right-hand grip rule.

Thanks! That's how I think of it too but I don't understand why it must minimize the change inside the loop and not outside the loop. If you grip it so that your fingers point out of the paper outside the loop, the current flows clockwise.

 

[kiwakwok]

The reason why we just consider the change in magnetic flux enclosed by the circuit is given in Faraday's law of induction.

Frankly speaking, I do not know why the law is established in this way due to my poor knowledge in Physics. (Sorry )
I also want to know whether it has any physical meaning or importance.