Properties of Electric Field Lines
The properties of electric field lines are:
1. Electric field lines originate from positive charges and terminate on negative charges. The lines never start or end in empty space because the electric field is created by the presence of charges.
2. The number of electric field lines leaving a positive charge is proportional to the magnitude of the charge and the number of lines entering a negative charge is proportional to the magnitude of the charge.
3. Electric field lines are continuous and unbroken. They do not have any breaks, gaps or sudden changes in direction, which means that the electric field has a continuous and uniform direction.
4. Electric field lines never cross each other because at any point in space, the electric field has a unique direction. If two electric field lines cross, it would mean that the electric field has two different directions at the same point, which is impossible.
5. The density of electric field lines is proportional to the strength of the electric field. The closer the lines are together, the stronger the electric field.
6. Electric field lines always point in the direction of the electric field intensity(E). If the electric field is uniform, the lines are parallel and evenly spaced. If the electric field is non-uniform, the lines are closer together in regions of higher field strength.
7. Electric field lines always point perpendicular to the surface of a charged object. The excess charge on the surface of the conductor will redistribute itself until the electric field lines are perpendicular to the surface. This is because if the electric field lines were not perpendicular, there would be a component of the electric field parallel to the surface, which would cause the charges to move along the surface and create an electric current. But in actual practice no electric current is observed on the surface of a charged conductor.
8. Electric field inside a conductor is zero. Inside the conductor, charges are free to move around and will redistribute themselves until they resides on the surface of the conductor(at maximum distance). So any excess charge resides on the surface of the conductor. This is known as the “Electrostatic shielding effect” of a conductor.
9. A charged particle need not follow an electric field line.
Reason:
Electric field lines show the direction of the electric field at different points in space — they are imaginary lines used to represent how the electric field acts on a small, stationary positive test charge at that point.
BUT charged particles in motion don’t necessarily follow these lines for several reasons :
⚙ 1. Inertia of Motion (Newton’s 1st Law):
- If a charged particle is already moving, it has momentum.
- The electric field exerts a force on it, but that force may not be exactly along the particle’s velocity.
- So the particle’s trajectory curves — it doesn’t jump to follow the field line immediately.
Think of it like a car going fast on a curved road: just because the road curves doesn’t mean the car immediately aligns with it — it turns gradually.
⚙ 2. Field Lines Represent Instantaneous Force — Not Path:
- Electric field lines show the instantaneous direction of force on a positive test charge at rest.
- A charged particle moving in that field responds to the net force, but its actual path depends on:
(i). its initial velocity
(ii). the strength and direction of the electric field
(iii). other forces acting on it (if any)
So, charged particles generally curve or spiral depending on these factors, instead of perfectly tracing the field lines.
⚙ 3. Only in Special Cases:
- If a charged particle starts from rest, and if the only force acting is from the electric field, then it will initially move along the field line.
- But as soon as it gains speed or other forces act (like magnetic fields or collisions), it may deviate.
In short : – Electric field lines represent the direction of force on a positive test charge placed at rest. However, a charged particle already in motion has inertia and may have a velocity component not aligned with the field. Thus, its path depends on the combined effect of the field and its initial motion, and need not follow the electric field lines exactly.
These properties of electric field lines help to visualize and understand the electric field around a charged object. They are important in many fields, including physics, electrical engineering, and telecommunications.