Electric Field Strength as a Vector along a line

[mickwess]

When Calculating Electric Field Strength using Q/kr^3, if the Q is negative is this negative disregarded? If not this would make E around a negative charge, negative. But if a positive test charge (q) is placed between two charges (Q1(negative) and Q2(positive)) then for Q1 (the negative charge) F will be negative becasue of the equation F=qE, and for Q2, F will be positive. The resultant of these forces is to be found by F1+F2, but this would mean that the resultant force F, would be smaller? And with one F being negative and the other not this suggests they act in different directions, which they dont!

 

[L-x]

E is a vector. Its direction is the direction of the force it will produce on a positively charged particle, in the case of the field due to a point charge no, you do not ignore the sign of the charge, but the expression you have is slightly wrong. It also involves the vector r, measured from the point charge.

Try drawing the problem and you should see where you are going wrong, you are measuring r from two different places.

 

[mickwess]

But one F will be positive and the other negative (they act the same way)

-0------------+q----------+0
Q1 Q2
<<<<<Both forces act this way<<<<

 

[L-x]

You are defining positive F to be the direction away from the particle in each case. This makes no sense if you are then trying to add the forces together in the way that you have done, because each force is defined relative to a different origin.

In this 1d case it makes more sense to say positive means pointing right, negative means pointing left, and thinking about where each F will be positive and where it will be negative.

 

[paranormal]

I would like to clarify that the electric field strength is a vector quantity, meaning it has both magnitude and direction. When calculating the electric field strength using the formula Q/kr^3, the negative sign of Q should not be disregarded. This negative sign indicates the direction of the electric field, and it is essential to consider it in the calculation.

In the scenario described, if a positive test charge is placed between two charges, one negative and one positive, the resultant force on the test charge would indeed be smaller. This is because the forces from the two charges would be in opposite directions and would partially cancel each other out.

However, it is not correct to say that the two forces act in different directions. Both forces act along the same line, with one being in the opposite direction of the other. This is why we use vector addition to find the resultant force, which takes into account both magnitude and direction.

In summary, the negative sign should not be disregarded when calculating electric field strength, as it represents the direction of the electric field. And the resultant force on a test charge placed between two charges will be smaller, but the two forces act along the same line, just in opposite directions.