Polar coordinates of an electric field

[netteo]

Homework Statement

Three charges are arranged as presented below. Q1= 5.00E-9C, Q2= 6.00E-9C and Q3= -7.00E-9C.

http://img15.imageshack.us/img15/9250/physicskf.png

D) Find the direction of the above electric field using the polar coordinate system 0°< θ <360°

Homework Equations

tan θ = o/a

The Attempt at a Solution

I found my

E₁ = 500
E₂ = 5400
E₃ = -700

Ex = 500 cos 18.4° + (-700) = -225.6
Ey = 500 sin 18.4° + 5400 = 5557.8

But the angle that I got was incorrect which was 24.63°.

Help anyone?

 

[SammyS]

Homework Statement

Three charges are arranged as presented below. Q1= 5.00E-9C, Q2= 6.00E-9C and Q3= -7.00E-9C.

http://img15.imageshack.us/img15/9250/physicskf.png

D) Find the direction of the above electric field using the polar coordinate system 0°< θ <360°

Homework Equations

tan θ = o/a

The Attempt at a Solution

I found my

E₁ = 500
E₂ = 5400
E₃ = -700

Ex = 500 cos 18.4° + (-700) = -225.6
Ey = 500 sin 18.4° + 5400 = 5557.8

But the angle that I got was incorrect which was 24.63°.

Help anyone?

You are finding the Electris Field at what location?

 

[netteo]

Oops, sorry about that. Point P (0.3m,-0.1m)

 

[SammyS]

Review the signs of your components .