Physics Review Question

Unit: Electricity and MagnitismYear: 1994 Question#: 32
Question: Electrons are flowing in a conductor as shown in the diagram below. What is the direction of the magnetic field at point P?


(1 ) toward the top of the page
(2 ) toward the bottom of the page
(3 ) into the page
(4 ) out of the page

What is this question really asking?




Explanation by: Sarah C (no last names)

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Answer 1
toward the top of the page

INCORRECT

This is the electric flow, pointing up towards the top of the page, not the magnetic field. To find out at point P you must use the first hand rule to find the magnetic field. return to top























Answer 2
toward the bottom of the page

INCORRECT

Even though the arrows may appear to be facing the bottom of the page, if you use the first hand rule and picture your fingers around the pole. They are not pointing down the page, are they? return to top



























Answer 3
into the page

INCORRECT

You need to use the first hand rule to determine the magnetic field. Your thimb must be facing the e-, of current, not down. This may be why you thought the lines were going into the page. return to top


























Answer 4
out of the page

CORRECT
To find the direction of the current you must use the first hand rule. Pointing your thumb (of your left hand) towards the electron flow (e-) Then the curl of your fingers are the magnetic field. Since at point P these lines point out of the page this answer is correct.  return to top


























What's this question really asking?

That you know how to use the first hand rule to find the magnetic field lines. As well as to be able to pictue it correctly. So that the fingers point in correct way. return to top

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