Magnitude and Direction of induced voltage

[rzn972]

Homework Statement

Hey everyone I have a physics e&m question: [/B]
http://blob:https%3A//www.physicsforums.com/aa779f37-be23-43d7-a888-d70263a3854b

Homework Equations

The Attempt at a Solution

I took the derivative to find the magnitude of the induced voltage. (do I need to add a constant c?)
I am having trouble with the direction of the current flow though... Do I use the right hand rule?

Thanks![/B]

 

[Simon Bridge]

I took the derivative to find the magnitude of the induced voltage. (do I need to add a constant c?)
I am having trouble with the direction of the current flow though... Do I use the right hand rule?

The constant "c" is usually either the speed of light in a vacuum or the constant of integration ... do either of these situation apply here?
The current flow is determined by the right hand rule in conjunction with a law of physics that applies to induced currents.
I'm puzzled you started at (c) ... did you do (a) and (b)?

 

[andrevdh]

4 a) Does the question ask for the magnetic (flux) ?

Oh, it should read the magnitude, not magnetic!

Shouldn't you use Faraday's law?

 

[Simon Bridge]

4(a) & (c) is Faraday's Law, 4(b) & (d) is Lenz's Law.
They probably want the the induced EMF ... since there is no clear indication of where the voltage should be measured between.
http://hyperphysics.phy-astr.gsu.edu/hbase/electric/farlaw.html#c1

 

[andrevdh]

There might be a small gap in the lower right-hand part of the loop

 

[Simon Bridge]

Well spotted - there may well be.

 

[rzn972]

Sorry! Yeah I meant magnitude.

 

[rzn972]

Okay so the derivative of magnetic flux is the induced voltage. I am having trouble calculating flux. Flux = BA cos (theta). How do I get the area...?

 

[Simon Bridge]

What shape is the area in question?

 

[rzn972]

Ahh I forgot that they gave us the length of the square. I think I was able to get it.

Does this look right?

 

[Simon Bridge]

in (c) and (d) the flux density is different in different parts of the square, how did you account for this?
(hint: the variable y should not be in your answer)
in (b) the question asks for the direction of the current

 

[rzn972]

For b) I say it is counterclockwise. My reasoning is that the field is decreasing as time passes (e^(-t)). The field will want to come out and the way to do that is for the induced current to flow counterclockwise.

I am not clear on c). Doesn't the y variable account for the different flux values for different y values?