Lenz's Law: Direction of Flux & Current

  • Thread starter Thread starter defetey
  • Start date Start date
  • Tags Tags
    Law Lenz's law
AI Thread Summary
When a magnetic field is suddenly switched off, a current is induced in the solenoid due to Lenz's Law, which states that the induced current will oppose the change in magnetic flux. The direction of the induced current will be counter-clockwise if the original magnetic field was directed upwards, as it attempts to maintain the magnetic field by creating a counteracting field. The current is generated because the change in magnetic flux occurs throughout the solenoid. The discussion raises questions about whether the counteracting magnetic field originates from within or outside the solenoid. Ultimately, the induced current's direction is determined by the need to oppose the reduction of the magnetic field.
defetey
Messages
12
Reaction score
0

Homework Statement



I don't have the question with me, it was on a test I did. It was something like this though:

A coil is placed vertically on a table. The magnetic field there is also vertical. If the magnetic field is suddenly switched off, in which direction would the current in the solenoid move?

A) Clockwise
B) Counter-clockwise
C) There would be no current
-and I forgot the rest of the choices.

The Attempt at a Solution



Well it would look something like this:

http://img43.imageshack.us/img43/2058/emfb.jpg

So, current is produced when there is a change in the magnetic field, so there is obviously would be current if the field is turned off. And that current's field would try to counter the flux.

But some things aren't clear to me;

1) Since the field is even on all points of the solenoid, which side of the solenoid (inner or outer) would be the one that creates the "counter-"magnetic field against the flux? Would the field be countered from within or from the outside?

2) Which direction would the flux be (that creates the current) if the "field is suddenly switched off"?
 
Last edited by a moderator:
Physics news on Phys.org
Your current would be counterclockwise. Lenz's Law states that this coil will attempt to fight the change in flux that is brought about when the B field is switched off. Since that original B field was pointed up, the current must be CCW to produce a B field in that same direction in an attempt "to fight" the change in flux from some flux to zero.
 
Kindly see the attached pdf. My attempt to solve it, is in it. I'm wondering if my solution is right. My idea is this: At any point of time, the ball may be assumed to be at an incline which is at an angle of θ(kindly see both the pics in the pdf file). The value of θ will continuously change and so will the value of friction. I'm not able to figure out, why my solution is wrong, if it is wrong .
TL;DR Summary: I came across this question from a Sri Lankan A-level textbook. Question - An ice cube with a length of 10 cm is immersed in water at 0 °C. An observer observes the ice cube from the water, and it seems to be 7.75 cm long. If the refractive index of water is 4/3, find the height of the ice cube immersed in the water. I could not understand how the apparent height of the ice cube in the water depends on the height of the ice cube immersed in the water. Does anyone have an...
Back
Top