Short Answer 
Electric field intensity is the force per unit charge experienced by a positive test charge, represented mathematically as E = F/q, with units in N/C or V/m. The direction of electric field lines varies based on charge type: they radiate outward from positive charges and converge inward for negative charges. Understanding these principles is essential for accurately describing electric fields.
Step 1: Understanding Electric Field Intensity
Electric field intensity is defined as the force per unit charge acting on a positive test charge at a given point in space. It is mathematically represented as E = F/q, where E is the electric field intensity, F is the force experienced, and q is the charge. The SI units used to measure electric field intensity are newtons per coulomb (N/C) or volts per meter (V/m).
Step 2: Direction of Electric Field Lines
The direction of the electric field is crucial in determining how it behaves around charges. Field lines indicate this direction and are influenced by the nature of the charges involved. Here are the principal rules governing the direction of electric field lines:
- For a positive charge (q > 0), field lines radiate outward.
- For a negative charge (q < 0), field lines converge inward.
- In the presence of two equal positive charges, field lines repel and spread apart.
- In an electric dipole, field lines start from the positive charge and end at the negative charge.
- For a uniform electric field, field lines are parallel and spaced equally, indicating constant strength.
Step 3: Identifying Suitable SI Units
When working with electric field intensity, understanding the appropriate units is important for clarity. The two correct SI units are: N/C or V/m. Using these units allows for consistent communication and calculation in the context of electric fields.