Electric field

Electric Field
Electric field can be defined as a space or region where a charged object experiences a force due to its charge. The positive charge q is usually called a test charge.

Field line
These are imaginary lines either straight or curved with property that the tangent of a field line at a certain point gives the direction of an electric field. Every single positive charge radiates an electric field line that comes out of the charge. In case of a negative charge it is directed towards the charge (opposite direction to the positive one). Moreover, it has been decided that one should take the direction of the field in which a small +ve charge would accelerate if placed in the field. Thus, considering what would happen if +ve charges are moved around in the same field.

Couloumb’s Law
In gravitational force, force between masses is given by Newton’s Law. The corresponding for an electric field is Coulomb’s law. It states that, the force experienced by two point charges is directly proportional to the square of their distance. Hence,
 * $$|\mathbf F|=k_e{|q_1q_2|\over r^2}\qquad$$

Whereby, F is force, $$q_1$$and $$q_2$$ are charges, r is the distance between the charges and $$k_e$$ is constant which is equal to 9x10⁹Nm²C⁻² Just as in gravitational fields, the coulomb’s law is applicable to spheres of charge which is the distance between the centers of the two spheres.

Electric Field Strength (E)


The space around a charge is different from a space with no charge present. This can be tested by bringing a small positive charge q into the provided space. In case, the charge q experiences some type of force then there is electric field, if not, there is no electric field (or it is zero). Therefore, as defined above, electric field is a space or region where a charged object experiences a force due to its charge. The positive charge q is usually called a test charge. E ⃗=(F/q) ⃗ As indicated in the formula above electric field is a vector quantity. The direction is that of the force of a positive charge would experience at the given point. The unit of electric field can be derived from the above given formula which is NC^(-1). The concept of electric field enables us to understand how force can transferred from one charge to another. Electric field strength in a uniform field. This can be created by placing two plates of equal and opposite charge parallel to each other as shown in the diagram below. The field line are parallel spaced. Therefore, if a test charge is placed at different locations in between the plates they will have the same force. In the figure below, if test charge q is place anywhere in between the plate, the E=F/q everywhere in the two plates.

Addition of field strength


Since we know that filed strength is a vector quantity, therefore, when fields from different negatively charged bodies act at a point their field strength are added vectorially. For instance let’s take a resultant field of body A and B as shown on the right. At A the fields act in the same line but on B a triangle has to be drawn to calculate the resultant field.

Application of electric field in medicine
There is evidence that alternating electric field seems to interfere with divisions of cancers cells and muscle stimulation

Links

 * 1) Carl R. Nave, Department of Physics and Astronomy []
 * 2) Joy Wagon, Electric field-A Electric Force, []
 * 3) Medgadget, Treating cancer with electric fields, []