Why Am I Getting the Wrong Electric Field Intensity Calculation?

[bluntz48]

i have been stuck on this problem for days and can't figure out where I'm going wrong. i have a rectangle with sides 6cm and 8cm. 3 points of the triangle have a point charge on them with the following values:

q1 = -2 * 10^(-8) C
q2 = 8 * 10^(-8) C
q3 = -4 * 10^(-8) C

The point charges are arranged such that q1 is on top right, q2 on top left, q3 on bottom left. Find the field intensity at the 4th point (bottom right).

So what I did is use E = kq/r^2 (k = 9*10^9) to find the field intensity on the 4th point. For q2 I broke it into x- and y- components with E2x = E2 cos 36.87 and E2y = E2 sin 36.87. For q2 I found the angle of 36.87 by doing the inverse tan of 0.06/0.08 = 0.75 and i found the distance between the two points by using the pythagorean theorum (a^2 + b^2 = r^2).

Once I have both E1 and E3 as well as E2 broken into components, I add up the ones on the x-axis (E2x, E3) and the ones on the y-axis (E2y, E1). Then again I use the pythagoren theorum to add up the resultant (Ex^2 + Ey^2 = R^2)

I keep getting the wrong answer and I don't know why. Could you please point out where I'm going wrong or list the steps I should be taking so I could compare. The answer on the sheet is 6.93 * 10^3 at an angle of 78.8 under the horizontal

thanks everyone!

 

[berkeman]

i have been stuck on this problem for days and can't figure out where I'm going wrong. i have a rectangle with sides 6cm and 8cm. 3 points of the triangle have a point charge on them with the following values:

q1 = -2 * 10^(-8) C
q2 = 8 * 10^(-8) C
q3 = -4 * 10^(-8) C

The point charges are arranged such that q1 is on top right, q2 on top left, q3 on bottom left. Find the field intensity at the 4th point (bottom right).

So what I did is use E = kq/r^2 (k = 9*10^9) to find the field intensity on the 4th point. For q2 I broke it into x- and y- components with E2x = E2 cos 36.87 and E2y = E2 sin 36.87. For q2 I found the angle of 36.87 by doing the inverse tan of 0.06/0.08 = 0.75 and i found the distance between the two points by using the pythagorean theorum (a^2 + b^2 = r^2).

Once I have both E1 and E3 as well as E2 broken into components, I add up the ones on the x-axis (E2x, E3) and the ones on the y-axis (E2y, E1). Then again I use the pythagoren theorum to add up the resultant (Ex^2 + Ey^2 = R^2)

I keep getting the wrong answer and I don't know why. Could you please point out where I'm going wrong or list the steps I should be taking so I could compare. The answer on the sheet is 6.93 * 10^3 at an angle of 78.8 under the horizontal

thanks everyone!

Sounds like your approach is right. The rectangle is 6 high by 8 wide?

Can you list the x and y components of E that you get for each of the 3 sources, so that we can check your math? E1 just points up, and E3 just points left, and E2 points down and to the right, correct?

 

[thomate1]

I would first like to commend you for your efforts in trying to solve this electric field problem. It can be frustrating when we get stuck on a problem for days, but it's important to remember that persistence and critical thinking are key in solving scientific problems.

From your explanation, it seems like you have a good understanding of the formula for electric field intensity and how to break down components. However, I would suggest double checking your calculations and making sure you are using the correct values for distances and angles. It's always a good idea to go back and check your work to catch any mistakes.

Another approach you could try is using vector addition to find the resultant electric field at the 4th point. This involves adding the individual electric field vectors, taking into account their direction and magnitude. This method may help you avoid any errors in breaking down components.

Additionally, it's important to note that the angle of 36.87 degrees for q2 may not be correct. It's always a good idea to draw a diagram and label all the given values to avoid any confusion.

I hope this helps guide you in the right direction. Remember to always double check your calculations and approach the problem from different angles if you're having trouble. Good luck!