lenz's law

[mano91]

can anyone explain this to me?
the law itself confuses me with its wording...
an example or two would be nice.
thank you all

[anonuser0511]

okay hmmm

"An induced current is always in such a direction as to oppose the motion or change causing it" -wiki

but that doesn't help much huh so...

here's how i do it.

change in flux increase => an induced flux in the opposite direction
change in flux decrease=> as induced flux in the same direction

e.g.
1. In this diagram (VCAA '07 Q14,15) once the switch is turned on there is an increase in current (nothing to something).
2. The current will produce a magnetic field (direction can be found using right hand rule) which will be an increase in flux (nothing to something).
3. Hence the induced flux will be in the opposite direction.
4. Then by the right hand rule the current's direction can be found.

Red - induced, Black - original

p.s. attached a nice picture of the file of a solenoid if right hand rule is too confusing (pretty much you have to have you hand going into the solenoid and wrap your thumb on the top coil)

[mano91]

is lenz's law induced CURRENT or VOLTAGE?
true tears says voltage on their cheat sheet.

[appianway]

Lenz's law gives the direction of the induced EMF. However, the induced EMF will be in the same direction as the current (conventional current flows from the point with the higher potential to the lower, and the EMF determines which direction this potential is in).

[IntoTheNewWorld]

Lenz's law gives the direction of the induced EMF. However, the induced EMF will be in the same direction as the current (conventional current flows from the point with the higher potential to the lower, and the EMF determines which direction this potential is in).

on VCAA exams sometimes they use induced current and sometimes they say induced EMF >_> what to do...

[appianway]

You should be able to say either, because they'll be in the same direction (unless an external EMF of greater magnitude and in the opposite direction is applied).

[crappy]

You should be able to say either, because they'll be in the same direction (unless an external EMF of greater magnitude and in the opposite direction is applied).

NO,you must say induced EMF. current is the result of the EMF.

[timoh]

okay hmmm

"An induced current is always in such a direction as to oppose the motion or change causing it" -wiki

but that doesn't help much huh so...

here's how i do it.

change in flux increase => an induced flux in the opposite direction
change in flux decrease=> as induced flux in the same direction

e.g.
1. In this diagram (VCAA '07 Q14,15) once the switch is turned on there is an increase in current (nothing to something).
2. The current will produce a magnetic field (direction can be found using right hand rule) which will be an increase in flux (nothing to something).
3. Hence the induced flux will be in the opposite direction.
4. Then by the right hand rule the current's direction can be found.

Red - induced, Black - original

p.s. attached a nice picture of the file of a solenoid if right hand rule is too confusing (pretty much you have to have you hand going into the solenoid and wrap your thumb on the top coil)

mate you're wrong with that picture showing the polarity of the two coils, currents right but gee get the north south right, youll confuse people

[appianway]

You should be able to say either, because they'll be in the same direction (unless an external EMF of greater magnitude and in the opposite direction is applied).

NO,you must say induced EMF. current is the result of the EMF.

Of course the current's the result of the induced EMF, but it hence follows that the current will be in the same direction (presuming that an external EMF in the opposite direction of greater magnitude is not applied, because the EMF acts as a vector). I don't see why they'd criticise you for stating that the flux must oppose the change in flux, creating an EMF which induces a current in whatever direction.

[crappy]

of fuck, my bad appian. I didn't even read the original problem, I thought you were saying a current was induced according to faradays law, I didn't know you were talking about directions.

[appianway]

Nah, it's OK.