Lenz's Law

[oxelhs]

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Can't understand the reasoning behind the question in passage II, #6 for the TBR physics chapter 8.

According to the content, if the loop is gaining Xs and creating Os, should be a CCW current and v.v.

The rod in this question is gaining Os so shouldn't the current be CW i.e. it goes from Y to X?

 

[Jepstein30]

Can't understand the reasoning behind the question in passage II, #6 for the TBR physics chapter 8.

According to the content, if the loop is gaining Xs and creating Os, should be a CCW current and v.v.

The rod in this question is gaining Os so shouldn't the current be CW i.e. it goes from Y to X?

For Lenzs law, just simplify things to "if it gains X, we need to gain Os" and vice versa.. so which way would the current need to flow to create Os? --> right hand rule

post the passage and I (or others) can help you out specifically

 

[oxelhs]

http://tinypic.com/r/otm53k/5

 

[oxelhs]

http://tinypic.com/r/otm53k/5

Perhaps I'm not able to visualize exactly what to do with the right hand rule here?
As it falls, the bar is gaining Xs correct? Is it just a simple matter of the thumb being the direction of the bar, fingers the magnetic field pointing up and thus palm is pointing from X to Y?

 

[Mopitt16]

Perhaps I'm not able to visualize exactly what to do with the right hand rule here?
As it falls, the bar is gaining Xs correct? Is it just a simple matter of the thumb being the direction of the bar, fingers the magnetic field pointing up and thus palm is pointing from X to Y?

As the bar falls, the area of the XYfa circuit decreases, and since magnetic flux is proportional to magnetic flux, the flux also decreases. Since the current already moves X to Y and yields a magnetic field moving upward from the base, to oppose the change in magnetic flux the current must be induced to increase the magnetic field within the loop, aka increase the current.

Magnetic flux = Magnetic field x Area, so a decrease in the area requires and increase in the magnetic field to keep a constant magnetic flux. The way to increase the magnetic field in a current loop is to induce an increase in the prevailing current. Hence, B.

 

[discowisco]

I think of it as le chatleirs (sp?), if you are increasing something you want to counteract it.

 

[Copernicium]

By pure coincidence I am having the same problems on this exact question. I cannot for the life of me understand why the answer is B and not C.

At first I figured that positive charges would gather at Y and negative at X, creating a current that goes Y -> f -> a -> X (pos to neg; Y to X). Then I looked at it from Lenz's law: Area is getting smaller, less dots coming out (if looking from above), so you need to create more with a counterclockwise current. You reach the same conclusion either way...

Clearly I'm missing something big here?

 

[oxelhs]

By pure coincidence I am having the same problems on this exact question. I cannot for the life of me understand why the answer is B and not C.

At first I figured that positive charges would gather at Y and negative at X, creating a current that goes Y -> f -> a -> X (pos to neg; Y to X). Then I looked at it from Lenz's law: Area is getting smaller, less dots coming out (if looking from above), so you need to create more with a counterclockwise current. You reach the same conclusion either way...

Clearly I'm missing something big here?

Yup, I'm still stuck on this :/