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Question 3 of 36

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SAT Subject Test

The set of lettered choices below refers to multiple questions.  Select the one lettered choice that best answers each question.  A choice may be used once, more than once, or not at all in each set.

The figure presents a rectangle containing a point charge and 5 labeled points. The point charge is in the middle of the rectangle horizontally and about one fifth of the way down from the top. At the same vertical level as the point charge are 3 labeled positions. Point A is to the far left of the point charge, point B is to the left of the point charge, about one fourth of the way toward point A, and point C is to the far right. Directly below the point charge is point E, about three fourths of the way down from the top. Points A, C, and E are all the same distance from the point charge. Point D is directly below point A and at the same vertical position as point E.

This question relates to a point charge plus Q fixed in position, as shown in the diagram. Five points near the charge and in the plane of the page are shown.

At which point will the magnitude of the electric field be least?

Select an Answer

Point A

Correct Answer: 

Point B

Correct Answer: 

Point C

Correct Answer: 

Point D

Correct Answer: 

Point E

Correct Answer: 

The correct answer is point D because it is farthest away from the point charge plus Q. The magnitude of the electric field E at any location due to a point charge is inversely proportional to the square of the distance r from the location to the charge, E mu 1 divided by r to the power of 2 end exponent, so the greater the distance, the less the magnitude of the electric field.

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