# I Lenz's Law

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1. Dec 14, 2016

### AaromTheBritt

I'm working on induction at the moment, and the math makes sense, but Lenz's Law is giving me trouble. Does anyone have an easier way (relatively) of remembering the directions of emf? Any advice is appreciated.

2. Dec 14, 2016

### cnh1995

Easier than? How are you currently determining the direction?

3. Dec 14, 2016

### ZapperZ

Staff Emeritus
As cnh1995 has stated, you have to be a bit more explicit than this, because how are we to know something that we have is "easier" than what you have when you didn't state exactly what you have?

Always remember that Lenz's law involves the CHANGE in the magnetic field. The induced magnetic field will try to OPPOSE THE CHANGE in the external magnetic field. It doesn't oppose the field, just the change in the field. This is what most students (and certainly, the students that I have encountered in my class) have trouble in comprehending.

I tend to have a simple, in-class demonstration of this effect by giving out a solenoid, a bar magnet, and an old-fashioned analog galvanometer to the students. I tell them to look at the deflection of the galvanometer as the push one end of the magnet in and out of the solenoid, and then look at the amplitude of the galvanometer deflection when the do that faster and slower. Then reverse the pole of the magnet and repeat.

You can practice the same thing virtually here: