Multiple choice confusion (1 Viewer)

[kaz1]

My opinion is that it is C as it is most perpendicular to the magnetic field. But in the answers it says it is B.

This is from the 2008 HSC.

 

[study-freak]

Answer: (B)
At X, the direction of motion is perpendicular to the magnetic field. Rate of change in magnetic field is at its greatest. Hence this is the answer.

Explanation for other choices:
(A), (C)
At W or Y, the direction of motion is parallel to magnetic field. Rate of change in magnetic flux is zero. Hence potential difference=0V.

You could have figured that (A) or (C) can't be the answer from the fact that they are at the same angle to the magnetic field and there is only one answer.

(D)
It's obvious that Z can't be the answer.

 

[shady145]

here are the graphs for potential difference and the angles.
View attachment 18854
this is for a AC motor
View attachment 18855
this is for a DC motor

as u can see at y the graph shows the value of V to be 0.
also study freak, the pt W does not appear to be a 180 degrees rotation to Y, so u couldnt just cancel it out

 

[shady145]

^thats out of the new excel. i think it has the same stuff in the old one too which can be found in the physics resource section

 

[Uncle]

Zero/Maximum flux means Maximum/Zero EMF
i.e. the flux and voltage graphs are 90 degrees out of phase of each other.
(further explanation may require calculus)

 

[shady145]

lol no ones commented about the picture being taken with a camera, my camera on my phone haha

 

[Uncle]

im sure it is in excel, the internet probably has good java applets on induced emf.

 

[mtsmahia]

Answer: (B)
At X, the direction of motion is perpendicular to the magnetic field. Rate of change in magnetic field is at its greatest. Hence this is the answer.

Explanation for other choices:
(A), (C)
At W or Y, the direction of motion is parallel to magnetic field. Rate of change in magnetic flux is zero. Hence potential difference=0V.

You could have figured that (A) or (C) can't be the answer from the fact that they are at the same angle to the magnetic field and there is only one answer.

(D)
It's obvious that Z can't be the answer.

I dont understand, how is it perpendicular ?

 

[youngminii]

I dont understand, how is it perpendicular ?

It's the metal strip we're talking about. At Y, the strip is moving parallel to the magnetic field. At X, the strip is cutting the magnetic field from the top (perpendicular).