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Have you ever wondered what causes lightning to strike when there is a storm? Why, in an atom, do electrons revolving around the nucleus not fly away, even though they are zooming at such high speeds?
Both of these are due to the same phenomenon, called an electric field.
An electric field is an area in space around an electric charge, in which another electric charge will experience a force. The electric field is measured in units of NC-1 (Newtons per Coulomb).
Electric charges exert forces on each other. Analogous to magnetic poles, like charges push each other away, and opposite charges pull each other together. A positively charged particle will attract a negatively charged particle, while repelling another positively charged particle. This relation of force on charges in an electric field is given by the formula:
E - Magnitude of electric field,
F - Force experienced by charge q,
q - A point charge.
If you redistribute the equation, you can deduce that a larger amount of force will be experienced by a larger charge. You can also see why the electric field's units are NC-1: force is measured in Newtons, and charge is measured in Coulombs, so F/q ≈ N/C.
Electric fields can be visualised as electric field lines. Electric field lines emerge from a positively charged particle but converge into a negatively charged particle. Electric fields for a positive particle emerge and continue on infinitely, while the fields of negatively charged particles originate from infinity and converge on the particle itself.
It is important to know that an electric field is a vector quantity.
Vector is a quantity having both a magnitude and a direction, while a scalar quantity only has a magnitude.
Therefore, electric fields may also be visualised using vectors. The resultant electric field at any point in space is the sum of all electric field vectors at that point.
Electric fields exhibit the following properties:
Electric field lines never intersect each other. If they did, it would mean that some point in space would have an electric field in two directions simultaneously, which is not possible.
Electric fields are strong where the electric field lines are closer to each other, and vice versa.
Electric fields are always perpendicular to the charged surface.
The number of electric field lines is proportional to the electric charge.
Electric field lines originate from the positive charge and terminate at a negative charge.
If there is only a single charge present, the electric field starts or ends at infinity.
It's easy to compare electric fields with magnetic fields. However, they do have some dissimilarities.
One stark difference is that magnetic field lines can only exist when there is a magnetic dipole i.e., both north and south poles are present. Since magnets cannot exist without either of their poles, magnetic field lines always form closed loops between the north pole and the south pole.
However, electric charges can exist as isolated positive or negative charges.
There are two types of electric fields.
As the name suggests, an electric field is called uniform when it does not change over distance. A charge (q) would experience the same magnitude and direction of force at any point in a uniform electric field.
As an example, consider the electric field between two oppositely charged parallel plates, as shown in the figure below.
Again, as the name implies, a non-uniform electric field is not constant and can vary from point to point. A charge (q) would experience varying magnitude or direction (or both) of force at different points, in a non-uniform electric field.
Consider the example below, which shows an electric field from a single point charge.
Electric fields emanating from subatomic charged particles (electrons and protons) hold an atom together. Without them, the atom would cease to exist, and by extension, everything else as well. Electric fields are also responsible for molecular interaction in chemical reactions.
Coulomb's law tells us that like charges repel each other, and unlike charges attract each other. But besides these rudimentary statements, Coulomb's law also provides the formula which quantifies this force of attraction or repulsion.
The force of attraction (or repulsion) between two point charges is:
2. Directly proportional to the product of the two charges
Therefore, the force between the point charges may be given as -
Where the proportionality constant k holds the value -
Where, ε₀ = 8.854 Nm2C-2 , is the permittivity of vacuum (also called the electric constant). If you calculate the value of k, it comes as k = 9*10^9 Nm2C-2 .
Since we know the formula for force acting on charge q2 due to charge q1, we can find the electric field strength due to charge q1 at point r. Just substitute the first equation with the equation that Coulomb's law gave us.
What really causes an electric field to form? How can you create an electric field? Electric fields are formed when there is a difference of electric potential between 2 points in space.
Electric potential is defined as the amount of work needed to move a unit charge from infinity to a point in an electric field.
Consider a charge Q. The electric potential at a point at a distance of r from the charge Q is:
In other words,
Substituting the proportionality constant, k = 1/(4πϵ0),
Velec is measured in Joules per coulomb, or Volts.
Create a small electric field yourself!
Take a plastic ruler/comb, and rub it on your hair or a piece of cloth. Bring it close to a small piece of paper. What do you notice? The paper seems to be attracted to the ruler. This is because rubbing the plastic causes it to acquire a static negative charge which has a static electric field around it. There is a potential difference between the ruler and paper; when the paper is in the proximity of this electric field, it experiences a force towards it.
Remember that we established that an electric field is the result of a difference in electric potential between 2 points? Mathematically, this can be expressed in the following way –
If you go ahead and differentiate Velec with respect to r, you will get the formula for the electric field. The negative sign indicates that electric field strength decreases as we go away from the charge (i.e. as r increases). Note that E and r are vector quantities in this equation, while Velec is a scalar quantity.
As stated earlier, electric potential energy is the energy required to move a charge through an electric field. Energy is required to move a charge through an electric field as the charge is constantly experiencing force due to the electric field. It can also be defined as the total energy required to hold a system of two charges in a particular configuration, due to the electrostatic forces between the two charges.
Consider 2 point charges q1 and q2, separated by a distance r. The electric potential energy of this system (Uelec) is given by:
When r is ∞ i.e., when the charges are very far apart, Uelec is 0. The work done on the charges to bring them at a distance of r is stored in this system as its potential energy. Conversely, the work done by the electrostatic forces of charges on each other is equal to the negative of potential energy of the system. Just like any other form of energy, Uelec is measured in Joules.
If you look closely at the equation for Uelec, You can deduce that you could get Uelec by multiplying electric potential by charge q. That gives us the potential energy required to hold one charge at a distance of r from another charge.
The nervous system of the body uses electric fields to transmit electrical signals from one neuron to another. Another example would be lightning strikes, which result from strong electric fields due to static charge build-up on the ground and in clouds during a storm.
Electric field strength depends on the magnitude of source charge, and the distance from it.
Electric field is the region around a charged particle in which other charged particles will experience a force.
1. Uniform electric field
2. Non-uniform electric field
Electric fields are used in capacitors in electronics.
What is an electric field?
Electric field is region around a charged particle in which other charged particles will experience a force.
What is the force experienced by a charge "q" in electric field "E"
F = q• E
If there is a single positive point charge. where do the electric field lines originate?
Point A has stronger electric field than Point B. Which of the following statements is true?
Electric field lines at A are denser than at B
There is a positively charged flat surface with surface vector pointing up. What is the direction of electric field lines?
q1 = 1C. q2 = -1C. distance between them (r) = 1m. What is the force on q2 due to q1, and in which direction?
F = 9*10^9 Newtons towards q1.
How can you create an electric field between surface A and surface B?
By creating an electric potential difference between the two surfaces.
q = 2C. Calculate the electric potential at point A which is 1m away from q.
What is the direction of electric field at point A due to a -2C point charge kept 100m from it?
Towards the Charge
Select the true statement(s)
Electric field lines tell us about the type of charge
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