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Questions and Answers
What is the relationship between electric field intensity (E) and potential gradient (dV/dr)?
Which of the following is a vector quantity?
What is the SI unit of electric flux?
What is the dimensions of electric potential?
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How is the electric field intensity due to a point charge $q$ at distance $r$ given?
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What is the value of the permittivity of free space (εo)?
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Which of the following is correct about the dielectric constant (K) for metals?
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How would the force between two charges change if the medium between them is replaced with a medium of dielectric constant K?
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How do electric field lines behave in the presence of charges?
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How is the force on charge q1 due to charge q2 related to the force on charge q2 due to charge q1?
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Study Notes
Coulomb's Law of Electrostatics
- Electrostatic force of interaction between two stationary charges is given by: F = 1 / 4π εo q1q2 / r2
- Permibility of free space (εo) = 8.85 * 10^(-12) C^2 / N-m^2
- Coulomb's law can be used in vacuum or air, for other mediums, εo is replaced by εoK or εoεr, where K is the dielectric constant or relative permittivity of the medium
Coulomb's Law in Vector Form
- Force on q2 due to q1: F12 = q1q2 / 4πε.r1 – r2 / |r1 – r2|^3
- Force on q1 due to q2 = – Force on q2 due to q1 (central forces)
- Electrostatic forces are conservative forces
Electric Field
- Electric field is the space around a charge where its influence can be experienced by other charges
- Electric field lines are imaginary lines or curves that tangent at any point is in the direction of the electric field vector at that point
- Electric field lines never intersect, begin on a positive charge, and end on a negative charge
- Electric field intensity (E) is the electrostatic force per unit positive charge at a point in electric field
- Electric field intensity is a vector quantity, direction is in the direction of electrostatic force acting on positive charge
- Electric field intensity due to a point charge q at a distance r: E = 1 / 4π εo q / r2
Electric Potential
- Electric potential at a point is the work done per positive charge in carrying it from infinity to that point in electric field
- Electric potential, V = W / q
- Electric potential is a scalar quantity
- Electric potential due to a point charge at a distance r: V = 1 / 4π εo q / r
Potential Gradient and Equipotential Surface
- Potential gradient is the rate of change of potential with distance in electric field
- Potential gradient = dV / dr
- Relation between potential gradient and electric field intensity: E = – (dV / dr)
- Equipotential surface is an imaginary surface joining points of same potential in an electric field
- Electric lines of force at each point of an equipotential surface are normal to the surface
Electric Flux
- Electric flux over an area is the total number of electric field lines crossing that area
- Electric flux through a small area element dS: φE = E.dS
- SI unit of electric flux: N – m^2/C
- Gauss's theorem: electric flux over any closed surface is 1 / εo times the total charge enclosed by that surface
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Description
Learn about Coulomb's Law of Electrostatics, which describes the electrostatic force of interaction between two stationary charges. Understand the formula and its variables, including permittivity of free space.
