Physics Help Forum Direction of Electric Field lines

 Electricity and Magnetism Electricity and Magnetism Physics Help Forum

 Mar 25th 2019, 04:43 PM #1 Junior Member   Join Date: Mar 2019 Posts: 1 Direction of Electric Field lines Hello, I understand how to get the magnitude for the electric field in this problem. My only issue is that I cannot figure out why the i coordinate is -sin while the j coordinate is -cos. I had the problem entirely right except I had cos in the i spot and sin in the j spot. I'm sure this is a very easy explanation, I just have been staring at it for a while and can't understand the logic behind it. Thank you. Attached Thumbnails
Mar 25th 2019, 05:46 PM   #2

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 Originally Posted by benmatt1999 Hello, I understand how to get the magnitude for the electric field in this problem. My only issue is that I cannot figure out why the i coordinate is -sin while the j coordinate is -cos. I had the problem entirely right except I had cos in the i spot and sin in the j spot. I'm sure this is a very easy explanation, I just have been staring at it for a while and can't understand the logic behind it. Thank you.
Two things.
1) The equation given for $\displaystyle \vec{E}$ (the first equation) shows a vector on one side and a scalar on the other. The idrection of $\displaystyle \vec{E}$ is radially outward from a positive point source. If you are dealing with a point source then you need to say that.

2) It is clear that you did not post the whole problem. Please do so, otherwise we can't help you with the question.

-Dan
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