Magnetic Flux Density (1 Viewer)

[Riceee]

Yes it may be an easy question...

 

[Fizzy_Cyst]

Yes it may be an easy question...

Magnetic flux density would remain constant.

Magnetic flux density is just another term used for magnetic field strength and this remains unchanged when the rod changes position.

 

[Riceee]

the answer said B
guess its wrong then

 

[s2 SEductive]

Where:
B = magnetic flux density in teslas
\phi = magnetic flux in webers (Wb)
A = area in square meters (m2)

As, the Area of decreases by the conductor AB, B increases as:
B is inversely proportional to A.


This is the only reason I can think of, so that the answer is B.

 

[Fizzy_Cyst]

heh, misread the q, thought it was asking about the rod itself.

The rod is moving in a magnetic field, hence current will be induced. Using RHP rule, current will be induced in conductor from b --> a. Using RHG rule, the mag field associated with this current foes into the page above conductor and out of the page beneath it.

Hence mag field strength (flux density) increases as more mag field lines run out of page in the loop abcd

Which paper is this q from?

 

[s2 SEductive]

Which paper is this q from?

CSSA 2010 physics

 

[romesh]

As, the Area of decreases by the conductor AB, B increases as:
B is inversely proportional to A.
This is the only reason I can think of, so that the answer is B.

I don't find this explanation plausible. You are correct that B corresponds to the 'magnetic flux density'. However, phi depends on A, because phi is measuring the amount of magnetic flux going through the loop. B is a property of the external field, and isn't changing. When you change the area of the loop, the variable that is changing is phi, not B. Thus as A decreases, B is constant and so in your equation, phi decreases.

I think Fizzy_Cyst's reasoning is correct- the key thing to note is that changing the size of the loop doesn't change the magnetic flux density arising from to B. Thus *any* induced field will increase the flux density.

 

[clementc]

Ahh I love the Catholics!! They give super good papers =D

As, the Area of decreases by the conductor AB, B increases as:
B is inversely proportional to A.

I think the important thing is that in the equation , B and A are independent of each other and the flux. So changing either of B or A will change the flux, but reasoning that because A decreases, B increases is incorrect, but that's just my 2 cents anyway.

The correct reason I think is due to Lenz's Law. So if it were a short response, I would define Lenz's Law (opposes change blahdeblah).
Then I would say that this sliding reduces the effective area of this loop, and thus flux passing through the loop.
By Lenz's Law, a current will be induced such that the magnetic field arising from this would act to oppose this change in flux (i.e. because flux has decreased, this will make the coil want to try increase the flux)
Thus, by the right hand curl rule, a current would be induced in the loop from D to C to B to A, giving rise to an induced magnetic field going up the page in addition to the external magnetic field.

(A lot of that explanation was actually not necessary but I've found that the best way, though discouraged, to stop markers trying to nitpick on the most trivial and dumbass things is to write EVERYTHING ==

ANyway, so hence magnetic flux density increases =D

 

[Fizzy_Cyst]

I'm spewing I have already written my trial paper... I would have liked to put this question in there =)

 

[imZerroo]

heh, misread the q, thought it was asking about the rod itself.

The rod is moving in a magnetic field, hence current will be induced. Using RHP rule, current will be induced in conductor from b --> a. Using RHG rule, the mag field associated with this current foes into the page above conductor and out of the page beneath it.

Hence mag field strength (flux density) increases as more mag field lines run out of page in the loop abcd

Which paper is this q from?

using RHPR, force is left, B is up, so current will be out of page, wouldn't it be a --> b then?
then use the RHSR, B decreases?

as for seductive's explanation, isnt the flux gonna decrease with area? i saw this question and i said it remains constant. so idk...

 

[Fizzy_Cyst]

using RHPR, force is left, B is up, so current will be out of page, wouldn't it be a --> b then?
then use the RHSR, B decreases?

as for seductive's explanation, isnt the flux gonna decrease with area? i saw this question and i said it remains constant. so idk...

Using RHPR, force is back up the ramp (to oppose the falling down the ramp) which means induced current from b --> a

Flux would decrease with area, but flux density would increase (due to induced current)

 

[clementc]

just out of interest, what is the RHSR? =P

 

[imZerroo]

close your fist, stick out your thumb.
in a current carrying conductor, thumb points to the flow of current and fingers curl around the conductor indicating magnetic field. make sure its your right hand as name suggests. :]

 

[imZerroo]

Using RHPR, force is back up the ramp (to oppose the falling down the ramp) which means induced current from b --> a

Flux would decrease with area, but flux density would increase (due to induced current)

ohhh to opppose !!! makes sense. thnks.