Electric Field Example

Calculate the magnitude of the electric field at point A by the  charges Q1 (positive, +20 mC) and Q2 (-20 mC).

 

The solution to this problem is similar to the one discussed in example 6. The difference is that now we are dealing with an electric field instead of force.

 

Approach

 

1. Find the magnitude of the field produced by each point charge

2. Use the equation E = kQ/r²

3. Add the components fo find the total field at point A

 

E_A1  = kQ₁/r₁²

 

E_A2 = kQ₂/r₂²

 

 

 

EA = E_A1 + E_A2 = kQ₁/r₁² +  kQ₂/r₂²

 

Note that the field lines from charge 1 point outwards and those from charge 2 point inwards toward the particle. These lines are indicated by the heavy arrows shown below.

 

 

The direction of the vector is calculated as in example 6