10.3 Questions 6,7,8.

[AskQuestions]

How do I do these questions?

[Lasercookie]

I'm assuming you're talking about the Heinemann book.

Q6a. Right hand slap rule. The induced current will be the direction of the force.Direction of force will be opposite to the motion (X to Y)
Q6b. Force will oppose the motion. The motion is to the right. (Left)

Q7a. Field is reversed, so therefore direction of current is also reversed. (Y to X)
Q7b. Again, force will oppose the motion. (Left)

Q8. Have a go at this one now that you've done 7 and 8.

edit: fixed my mistake,

[AskQuestions]

I'm sorry, but could you please explain question 6 again?

[Lasercookie]

Oops sorry, made an error typing out question 6a. Sorry if I confused you. 

Induced currents set up by the relative motion of a conductor and magnet will create a field that will apply a force that will oppose the relative motion. This is the situation in question 6.

So the direction of motion is to the right, the induced current will create a force that will oppose it.
So the direction of the force will be left (palm).
The field is out of the page/upwards (fingers)
This leaves your thumb pointing south (X to Y).

6b is the same principle. I already figured out the direction of the force when working out 6a.

[AskQuestions]

Oops sorry, made an error typing out question 6a. Sorry if I confused you. 

Induced currents set up by the relative motion of a conductor and magnet will create a field that will apply a force that will oppose the relative motion. This is the situation in question 6.

So the direction of motion is to the right, the induced current will create a force that will oppose it.
So the direction of the force will be left (palm).
The field is out of the page/upwards (fingers)
This leaves your thumb pointing south (X to Y).

6b is the same principle. I already figured out the direction of the force when working out 6a.

Thanks for the explanation.
I get the reasoning, but I thought that the B induced should oppose the change in magnetic flux hence it is into the page?
I know you're right, but how would I differentiate between field directions?

[Lasercookie]

Thanks for the explanation.
I get the reasoning, but I thought that the B induced should oppose the change in magnetic flux hence it is into the page?
I know you're right, but how would I differentiate between field directions?

From what I know, what actually happens is that the induced current creates the induced field.

When in the current is in a loop, this induced field opposes the change in the flux that produced it. With relative motion, the situation in Question 6, the field created by the induced current applies a force that opposes the motion.

Wikipedia describes Lenz's Law as "An induced current is always in such a direction as to oppose the motion or change causing it".  So I don't think it matters which way you look at it (flux is opposed or motion is opposed), but there always has to be some form of opposition (in order to not violate the conservation of energy).

When applying the right hand slap rule, both the field and the force cannot be reversed in direction at the same time; It would be like simply rotating the vectors, not actually changing anything.

It's kind of confusing and I don't really understand this beyond the right hand rule, but this makes some sense to me. Try playing around with this applet: http://www.phy.syr.edu/courses/java-suite/crosspro.html. Reverse the direction of A and see what happens. Then reverse the direction of A and B and then see what happens to C. Khan Academy has some videos on the cross product in the physics section - I haven't watched them yet, but they should clear things up.

If you look at it as if the field is opposing the change in magnetic flux, but this would mean that the direction of motion would have to remain the same. So you'd have field into the page, force to the right which leaves the thumb point south. Which is X to Y, the same answer.

Feel free to correct me. I'm not 100% sure on this (I think I contradicted myself somewhere), someone else might want expand on it.