Physics Review Question

Unit: Electricity and Magnetism
Year: 1997 Question#: 34
Question: The diagram below represents the magnetic field around point P, at the center of a current-carrying wire. What is the directon of electron flow in the wire?


(1 ) from A to B
(2 ) from B to A
(3 ) from P into the page
(4 ) from P out of the page

What is this question really asking?




Explanation by: Rachel M
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Answer 1
from A to B

INCORRECT

You would have gotten this answer if you used your right hand instead of your left hand with the first hand rule. Since the flow of electrons is negative, you should use your left hand. Use the right hand with a positive flow. Try again. return to top



















Answer 2
from B to A

CORRECT

You should use the 1st hand rule because there is no force involved in the problem and you should use your left hand because the flow of electrons is negative. Using this, make your thumb the electron flow and your fingers the magnetic field. Thus the flow will go from B to A. return to top



























Answer 3
from P into the page

INCORRECT

You might have gotten this answer if you used the 3rd hand rule with an open palm on your left hand and made your palm the direction of the electron flow. You got the correct hand (left), but what you thought was the flow is actually the force, and there is no force in this problem. You should use the 1st hand rule (closed palm), with your thumb as the electron flow. Try again. return to top





























Answer 4
from P out of page

INCORRECT

If you used your right hand and the 3rd hand rule, thought that your palm was the electron flow, and used your fingers as the magnetic field, then you would've gotten this answer. However, you need to use your left hand because the flow is negative, the 1st hand rule (closed palm) because there is no force in the problem, and use your thumb as the electron flow. Try again. return to top






























What's this question really asking?

Do you know the hand rules and how to apply them to pictures and problems? Which hand do you use and why? return to top