Skip to main content

Coluomb’s law

We know that two charged bodies  either attract or repel each other. Like charges repel each others and unlike charges attract each others.  Coulomb’s Law attempts to define the force that is exerted when the two bodies are attracted or repelled because of their charges.


Coulomb’s Law states that:


The force exerted between two stationary point charges:


i. Is directly proportional to the product of charge strength of the two charges.


ii. Is inversely proportional to the square of distance between the two charges.


Mathematically the Coulomb’s law can be represented as:
F \propto Q_1 \times Q_2 \;\;\;\; ..i                   and                        F \propto \frac{1}{r^2} \;\;\;\; ..ii


Where, F = Force of attraction between the two particles ,Q1 = charge of first particle , Q2 = charge of second particle and r = distance between the two particles.


Combining equation i and ii we get:
F \propto \dfrac{Q_1 \times Q_2}{r^2}


Now if we replace the proportionality by the constant of proportionality (K ) then we get:


F = K \times \dfrac{Q_1 \times Q_2}{r^2}


The constant of proportionality (K ) is called the Dielectric Constant and given as :


K = K_e \times \frac{1}{\epsilon_r}
Where, K_e Is the Coulomb’s constant or electrostatic constant and


\epsilon _r = relative Permittivity.


The Value of Coulomb’s Constant is:


K_e = \dfrac{1}{4 \pi . \epsilon _0} ,                   Where, \epsilon _0 = Permittivity of vacuum.


Thus, The final formula of  Coulomb’s Law after we place the value of constant of proportionality (K ) can be summarized as following:


F = \dfrac{Q_1 \times Q_2}{4 \pi \epsilon_0 \epsilon_r r^2}


And the exact value of Coulomb’s Constant is:
K_e = \dfrac{1}{4 \pi 8.854 \times 10 ^{-12}} = 8.9875 \times 10^9 N.m^2.C^{-2}


Coulomb’s Law is valid only under following circumstances:


a. The two charged bodies should be  a point charge.


b. The two charged points should be stationary with respective to each others.

Comments

Post a Comment

Popular posts from this blog

Lorentz force equation

  Lorentz Force Equation   The force experienced by current element in magnetic field is given as sum of force due to electric field and magnetic field.   Force due to electric field: A region is said to be characterized by an electric field if a particle of charge q moving with a velocity v experiences a force Fe, independent of v. The force, Fe, is given by              F e = qE ---------------------------------------- (1.1)                    E is the electric field intensity. Measured in newtons per coulomb (N/C) or volts per meter. Where volt is a newton-meter per coulomb. The line integral of E between two points A and B in an electric field region gives voltage between A and B. It is the work per unit charge done by the field in the movement of the charge from A to B. Force due to magnetic field: If a charged particle experiences a force which depends on v, then the region is said to be characterized by a magnetic field. The force, Fm, is given by                     F m =...

relay

A relay is an electrically operated switch. These are remote control electrical switches that are controlled by another switch. A relay is used to isolate one electrical circuit from another. It allows a low current control circuit to make or break an electrically isolated high current circuit path. The basic relay consists of a coil and a set of contacts. The most common relay coil is a length of magnet wire wrapped around a metal core. When voltage is applied to the coil, current passes through the wire and creates a magnetic field. This magnetic field pulls the contacts together and holds them there until the current flow in the coil has stopped. The diagram below shows the parts of a simple relay. Operation: When a current flows through the coil, the resulting magnetic field attracts an armature that is mechanically linked to a moving contact. The movement either makes or breaks a connection with a fixed contact. When the current is switched off, the armature is usually returned by...

Maxwell equations

Maxwell equations: The electric and magnetic fields are governed by a set of four laws, known as Maxwell’s equations. Maxwell’s equations form the basis for the entire electromagnetic field theory. Max well’s equations in integral form: 1. Faraday’s law:                         A time-varying magnetic field gives rise to an electric field. Specifically, the electromotive force around a closed path C is equal to the negative of the time rate of increase of the magnetic flux enclosed by that path, that is,      2. Ampere’s circuit law: Time varying electric fields give rise to magnetic fields. Specifically, the magnetomotive force (mmf) around a closed path C is equal to the sum of the current enclosed by that path due to actual flow of charges and the displacement current due to the time rate of increase of the electric flux (or displacement flux) enclosed by that path; that is,         3. Gauss law of electric field: Gauss’ law for the electric field states that electric charges give ...