- Electric Field Intensity Definition: Electric field intensity is defined as the force acting on a unit positive charge within an electric field.
- Coulomb’s Law: Coulomb’s law describes the force between two charges based on their magnitudes and the distance between them.
- Calculation of Electric Field: The electric field strength at a point is determined by the force on a unit positive charge at that point.
- Units and Vector Nature: Electric field strength is measured in Newtons per Coulomb (N/C) and is a vector quantity, meaning it has direction.
- Resultant Electric Field: The total electric field strength at a point with multiple charges is found by adding up the individual field strengths vectorially.
Electric field strength or electric field intensity is another name for the electric field. Electric field strength can be determined from Coulomb’s law. According to this law, the force ‘F’ between two point charges Q1 and Q2 coulombs placed a distance d meters apart is given by,
Here, εo is the permittivity of vacuum = 8.854 × 10 – 12 F/m and εr is the relative permittivity of the surrounding medium.
Now let us put Q2 = + 1 Coulomb in equation (1) and denote the force F by E. This substitution gives,
This equation gives the force acting on a unit positive charge placed a distance d from charge Q1.
By definition, that force is the electric field strength of charge Q1 at distance d from the charge. We now have the expression for electric field strength or intensity. Combining it with equation (1), we get,
This expression shows that if we place a charged body at any point in an electric field, the product of the electric field strength at that point and the charge of the body equals the force acting on the body there. The expression can also be rewritten as,
Based on this expression, the electric field strength is expressed in newtons per coulomb (N/C). Because electric field strength has direction, it is a vector quantity. Intensity refers to magnitude or amount, so electric field intensity means the magnitude of the field strength. In summary, electric field intensity or strength is written as:
We have discussed the electric field intensity at a point due to a single charge. When several charges influence the same point, we first calculate the electric field strength there for each charge, then add all the individual strengths vectorially to find the resultant field strength at that point.
