Calculate the component of the electric field

AI Thread Summary
The discussion focuses on calculating the electric field components at point P due to two point charges, A (+2.0 nC) and B (–3.0 nC), which are 200 mm apart. For part (i), only the positive charge A is considered because it creates an electric field directed away from itself, while for part (ii), the negative charge B is used as it generates an electric field directed towards itself. The calculations utilize the formula E = kQ/(r^2), where k is a constant. Participants clarify the reasoning behind using different charges for each calculation based on their respective electric field directions. Understanding the direction of the electric fields due to each charge is crucial for accurate calculations.
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http://img367.imageshack.us/img367/5459/69671206ju9.th.jpg

See image above. Point charges A, of +2.0nC, and B, of –3.0 nC, are 200mm apart in a vacuum, as shown by the figure. The point P is 120mm from A and 160mm from B.

(i) Calculate the component of the electric field at P in the direction AP.
(ii) Calculate the component of the electric field at P in the direction PB.

The markscheme uses E= kQ/(r^2)

where k = 1/4*pi*epsilon

However, for part (i), uses only the 2nC charge, while uses only the -3nC charge for part ii - can someone please explain why this is the case.

Thanks
 
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In what direction is the field at P due to A? Due to B?
 
ahh yes, i understand now, thanks
 
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