Falling Loop in Magnetic Field: How long to leave field?

[dekoi]

Question:

0.2m x 0.2m metal loop is oriented vertically.
mass = 10g
resistance = 0.010Ω
magnetic field = 1.0 T
The magnetic field is horizontal (into the page), perpendicular to the loop, and fills the top half of the loop. There is no magnetic field in the bottom half of the loop.
The loop is released from rest and allowed to fall.

a) Show that the loop reaches a terminal velocity, and find a value for it.
b) How long will it take the loop to leave the field? Assume the time needed to reach the terminal velocity is negligible. How does this compare to the time it would take the loop to fall the same distance in the absence of a field?


My Answer:
a) I am uncertain of whether there is a force exerted on the loop by the magnetic field. I would assume that the force acts in the horizontal direction, which would not affect the vertical motion of the loop. However, as the loop falls, it is no longer perpendicular to the magnetic field, and therefore creates an angle which will in turn create a force... ?
So if there is a force, then the equation is F = ILBsinΦ. However, I do not have a value for current, and I do not see a way of finding it.

b) I have not attempted part b) yet, since I have not even finished a). However, if you have any hints, please provide me with them.

Thank you.

 

[Gokul43201]

Question:

0.2m x 0.2m metal loop is oriented vertically.
mass = 10g
resistance = 0.010Ω
magnetic field = 1.0 T
The magnetic field is horizontal (into the page), perpendicular to the loop, and fills the top half of the loop. There is no magnetic field in the bottom half of the loop.
The loop is released from rest and allowed to fall.

a) Show that the loop reaches a terminal velocity, and find a value for it.
b) How long will it take the loop to leave the field? Assume the time needed to reach the terminal velocity is negligible. How does this compare to the time it would take the loop to fall the same distance in the absence of a field?


My Answer:
a) I am uncertain of whether there is a force exerted on the loop by the magnetic field. I would assume that the force acts in the horizontal direction, which would not affect the vertical motion of the loop.

Why do you say the force would be horizontal ? How do you calculate what the force will be (magnitude and direction) ?

 

[dekoi]

Gokul:
If there is a force, then the equation is F = ILBsinΦ. However, I do not have a value for current, and I do not see a way of finding it.

 

[Gokul43201]

Look at your thread title again. Do you know what that term means ? If not, ask Faraday !

 

[dekoi]

Gokul,
You are only confusing me, and are not helping me in any way to answer the problem.

Does anyone else have any advice?

 

[inha]

The key to solving this was mentioned in the thread title, induction. Gokul pointed it out so he was helping you. As the magnetic flux through the loop changes what happens?

 

[dekoi]

It's okay... I've figured it out.