How can I quickly determine the direction of induced current using Lenz's Law?

[flyingpig]

Homework Statement

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The Attempt at a Solution

Alright in the picture you see two hands (YES THEY ARE HANDS).

The one my book says is to use your palm and let your palm be opposite to v and other fingers go into the page and your thumb will tell you your direction of the current.

I have only one problem with this, if my thumb is going up, how am I suppose to tell (quickly without reasoning to changing flux and such) which way will the current flow?

Now for my curling one. Our professor taught us using that, he said to point your thumb into the B-field and curl your fingers and they will be in the direction of the induced current.

Here is my problem. I am curling and I get my induced current to be clockwise, how do I get it counterclockwise? My professor's hand had nothing to do with the velocity

 

[da_nang]

Here's what I'm used to do. For positive particles, with right-hand thumb and index finger form a gun and middle finger pointing out, the thumb represents the force, index velocity and middle magnetic field. For current, the index is direction. For a straight conducting wire inducing a magnetic field, keep the right hand in an open thumbs-up position rotating the hand. Thumb then becomes the current's direction and the other fingers the magnetic field's direction. For loops with changing flux, switch the current and magnetic field directions. If Lenz's law becomes a problem to memorize, switch to the left hand to get the current direction.

 

[flyingpig]

Let's try your left hand method, because I have not a clue on your right hand lol

 

[da_nang]

Basically, Lenz's law states that a loop will induce a magnetic field to counteract the change in flux. Say the flux increases, then the loop induces a magnetic field in the opposite direction of the previous magnetic field to counter the increase in flux. With the right hand method, you want to point the thumb in the opposite direction of the magnetic field to get the current's direction. Should the magnetic field go into the page, then the thumb should point out of the page since the loop wants to counter the flux increase. The current then goes counterclockwise.

The idea with the left hand method is to skip the step where you figure out which way the induced magnetic field should go, since it applies to negative charges. The right-hand method is for positive charges. The current is through conventions defined as the movement of the positive charges, and since the loop wants to counteract the increase in flux, the current should go the opposite way i.e. in the negative charge's direction.

Beware though, that should the flux decrease, then the current wants to strengthen the magnetic field. In this case, use the right hand method and point the thumb in the direction of the magnetic field to get the current's direction.

 

[flyingpig]

Does that also mean that the current will tell your positive and negative terminals of your induced emf (the conducting bar) then?