A long straight wire lies on a horizontal table and carries an ever-increasing c

Question

A long straight wire lies on a horizontal table and carries an ever-increasing current northward. Two coils of wire lie flat on the table, one on either side of the wire. When viewed from above, the induced current circles:

I used to be really good at this. okay so my thumb would be point up (correct?) and my fingers curl counterclockwise, but after that i am lost.

i know the answer is counter clockwise in the east coil and clockwise in the west coil but i missing some steps on how exactly to get that.

Please& thank you for any help!

Explanation / Answer

Here you have to use the Right Hand Rule where the current and Magnetic field lines are perpendicular to each other. To do this you simply place your RIGHT thumb aligned with the middle current carrying wire. Your fingers will tell you the direction of the magnetic field lines, what you do is keep your thumb aligned with the middle line and then "curl" your fingers. If you do this, the the one to the east of the middle wire will have your fingers go through the middle, and the fingers will come out or away from the wire to the west.

Then using these directions as the Magnetic field lines, you now do the same Right Hand Rule, but now the fingers will represent the current and the thumb is aligned to each of the directions that you found for the Magnetic field lines. In other words, the East wire will have (using the Right hand rule again) the thumb pointing inwards, and the fingers go or curl CLOCKWISE - but the current goes COUNTERCLOCKWISE due to Lenz Law. In the west wire the thum points out of the plane of the wire and the fingers curl COUNTERCLOCKWISE, so the current actually goes CLOCKWISE, again according to Lenz Law. So the answer is D.

The key is knowing that you have to apply the RIGHT HAND RULE twice, and that the thumb can represent the current or the Magnetic field, and the fingers point in the direction of the other, and need to use Lenz Law correctly to get the right answer.

This is a very good question and I think you genuinely want to understand it - most people just get frustrated and give up. Keep the questions coming and ask for further clarification if you need more info.

Related Questions

Navigate

• Browse (All)
• Browse A
• Subjects

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.