# Aqa A level physics Electric field question (1)

For this question I don’t really understand how go about it,
My attempt is the one is blue and the markscheme is the green box
-why are the arrows both going away from P if there’s 2 opposite charges ?
(edited 2 months ago)
For one, the electric fields are acting on the particle P, so the arrows should start from the point P

Secondly, Electric field lines always point away from a positive charge and towards a negative charge.
You can imagine it as the positive charge 'pushing' the point P, while the negative charge is 'pulling' it.

Finally, since one charge is bigger in magnitude than the other one, the resultant force will point more towards that bigger vector- in effect it will be like a parallelogram as you add 2 vectors.
Hope that helps
(edited 2 months ago)
Original post by 1234kelly
For this question I don’t really understand how go about it,
My attempt is the one is blue and the markscheme is the green box
-why are the arrows both going away from P if there’s 2 opposite charges ?

You may want some visualisation of how to draw the electric field vector at P. Here is it goes.
Step 1: Connect the charge of +4.0 nC to point P with a straight line. Do this for the -8.0nC charge, too. This is shown below.

Step 2: Electric field vector due to positive charge is pointing outward radially while the electric field vector due to negative charge is pointing toward itself radially.
Note the magnitude of charge for the negative charge is twice that of the positive charge, so the electric field vector due the negative charge has a length that is twice that of the positive charge. This is shown below.

The electric field vector must be drawn along the imaginary line connecting the point charge and the point.

Note that you can do away step 1 once you know how to draw the electric field vector.