Unit: Electricity and Magnetism
Year: 1994 Question#: 24
Question: The electrostatic force between two positive point charges is F when the charges are 0.1 meter apart. When these point charges are placed 0.05 meters apart the electrostatic force between them is
(1 ) 4F and attracting
(2 ) F/4 and attracting
(3 ) 4F and repelling
(4 ) F/4 and repelling
What is this question really asking?
Explanation by: Gabriel F
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Answer 1
4F and attracting
INCORRECT
The value is correct because Coulombs law
states that if you cut the distance between two objects in half, then the attraction
between the objects is quadrupled. However the two like charged objects would not
attract.
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Answer 2
f/4 and attracting
INCORRECT
This answer is wrong because according to Coulombs law
if the distance is cut in half, then the attraction between the objects are quadrupled,
not quartered.
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Answer 3
4F and repelling
CORRECT
This answer is correct because according to Coulombs law
, if the distance
(r) is cut in half, then the force is quadrupled and since they are
like charges they would repel.
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F/4 and repelling
INCORRECT
They would repel, but your use of the formula
is flawed.
return to top What's this question really asking?
It is asking for the relationship between the distance of 2 objects and the attraction of the two. It is a "classic" (you'll see at least one question like this on the exam) inverse square law problem.
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