Electrical Fields
Definition
An electrical field is a region of force around a charged object, it is similar to the concept of a magnetic field around a bar magnet. The lines of force can exert an attraction or repulsion on other charged objects to induce movement of the charged objects.
The lines of the electrostatic force field spread outwards from a positive charge and head inwards towards a negative charge, as illustrated in the diagrams above.
Any charge placed within these fields will feel the force, if the force is large enough the charge will move. Depending on the charges they will either be attracted or repelled.
Example
The lines of the electric fields combine to produce a force of attraction.
Shapes of Electrical Fields
The shape of an electric field depends on the shape of the charged object.
__Point Source __
When the source of the charge is a single point the electric field surrounds the point and spread out in a curve about the point.
Protons and electrons are examples of a point source of charge. They are small well defined areas of charge and have a regular field around them, as illustrated in the diagram of a proton’s electric field.
Parallel Plates
If the charge is applied to two metal plates with a narrow gap separating them, the lines of the electronic field pass from the positively charged plate towards the negative plate, creating parallel lines of force between the two plates.
When drawing a force field diagram, for either a point source or between objects like the parallel plates, the concentration of the lines represents the strength of the field. In the diagram above the electric field on the right is twice the strength of the one on the left.
If a charged point source is placed in the field from the plates the lines of field will produce a force to deflect the point source, as illustrated below.
Electrical Fields and Static
The effects of static electricity can be explained using the concept of the electrical field that surrounds all charged particles.
When lines of an electric field meet they produce a force. Like all forces this produces movement if the force is large enough to overcome the inertia of the charged particles. Electrons have no mass compared to a proton, so they are easier to move and require only a small electric field strength to displace them.
- Like charges repel.
When two like charge come together the lines of the electric fields from each particle push against each other resulting in them moving away from each other, repulsion.
The diagram illustrates the electric field interaction of two protons.
- Unlike charges attract.
When two particles of an opposite charge are brought together the electric field lines act in the same direction and result in the particles moving closer together, attraction.
The diagram illustrates a proton’s and an electron’s electric fields interacting.
- Induction
Induction is the process of creating a local area of charge by placing another charged object close by. The lines of force then move the electrons in the second object leaving behind the positive nuclei, thus creating an area of charge.
The illustrations below shows this process.
When the charged balloon is held away from the wall the electric fields are too weak to interact so the electrons in the wall remain evenly distributed. The wall is electrically neutral at this stage.
When the balloon is placed close to the wall the electrical fields interact and the electrons in the wall near the balloon are displaced. This leaves the positive nuclei in place, producing an area of positive charge.
- What would happen to an beam of electrons passing between two metal plates if one plate was negative in charge and the other positive in charge?
- bend
Explanation: The electrons would be attracted to the positive plate and repealed from the negative, the beam would bend in the direction of the positive plate.