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Why does the unit vector r-hat always point away from a charge?

by negation
Tags: charge, point, rhat, unit, vector
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negation
#19
Apr11-14, 01:15 PM
P: 819
Quote Quote by Doc Al View Post
Ah, now I see what's going on. Chestermiller is right.

When using Coulomb's law in vector form, that unit vector always points outward from q1. Then you can use the signs of q1 and q2 to determine the direction of the force that q1 exerts on q2. When they have the same sign, the force acts in the direction of the unit vector.

The unit vector just describes the direction from q1 to q2.
and if the force were from q2 to q1? the unit vector would point to the left?

In the second diagram however, the electric force is from q2 to q1 yet the unit vector points to the right of q2.
craigi
#20
Apr11-14, 01:28 PM
P: 421
Quote Quote by negation View Post
Isn't i-hat one unit component of x?

The mathematical definition is e1 or vector r / magnitude r
You're close, but this isn't quite correct. Where are you learning this from?
Doc Al
#21
Apr11-14, 01:31 PM
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P: 41,471
Quote Quote by negation View Post
and if the force were from q2 to q1? the unit vector would point to the left?
No, the unit vector describes the direction from q1 to q2. The force may be in the same direction or in the opposite direction, depending on the signs of the charges.

In the second diagram however, the electric force is from q2 to q1 yet the unit vector points to the right of q2.
That's right.


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