Electric Field Intensity / Electric Field Strength (E) - Field Theory.
- Electric field due to a charge is the space around the unit charge in which it experiences a force.
- Electric field intensity or the electric field strength at a point is defined as the force per unit charge.
Mathematically,
E = F / Q
OR
F = E Q
- The force on charge Q is the product of a charge (which is a scalar) and the value of the electric field (which is a vector) at the point where the charge is located.
- Hence force will be either parallel or anti-parallel to the Electric field intensity.
(i.e. Q > 0) the force F points in the same direction as the electric field E.
- If the charge is negative (i.e. Q < 0) the force F points in the opposite direction as the electric field E.
- Electric field intensity(E) at point r due to a point charge Q located at a point with position vector r1 is given as:
Similarly for N point charges Q1, Q2 ….Qn located at points with position vectors r1, r2,….rn, the electric field intensity at point r is given as:
- Charges can occur as point charge, line charge, surface charge and volume charge.
The charge element dQ and the total charge due to different charge distribution is given as:
dQ =ρldl → Q = ∫L ρldl (Line Charge)
dQ = ρsds → Q = ∫S ρsds (Surface Charge)
dQ = ρvdv → Q = ∫V ρvdv (Volume Charge)
- Electric field intensity due to different charge distribution is hence given as:
ELECTRIC LINES OF FORCES:
- Electric line of force (also called Electric Flux lines or Streamlines) is an imaginary straight or curved path along which a unit positive charge tends to move in an electric field.
PROPERTIES OF ELECTRIC LINES OF FORCE:
- Lines of force start from positive charge and terminate either at negative charge or move to infinity.
- Similarly lines of force due to a negative charge are assumed to start at infinity and terminate at the negative charge.
- Lines of force never intersect i.e. they do not cross each other.
Tangent to a line of force at any point gives the direction of the electric field E at that point.
- Lines are dense close to a source of the electric field and become sparse when one moves away.
-The number of lines per unit area, through a plane at right angles to the lines, is proportional to the magnitude of E. This means that, where the lines of force are close together, E is large and where they are far apart E is small.
IMPORTANT POINTS:
- If there is no charge in a volume, then each field line which enters it must also leave it.
- If there is a positive charge in a volume then more field lines leave it than enter it.
- If there is a negative charge in a volume then more field lines enter it than leave it.
- Hence we say
“Positive charges are sources and Negative charges are sinks of the field.”
ELECTRIC FLUX DENSITY(D = εE):
- Line of Force may be termed as ‘Electric Flux’ represented by ψ and unit is coulomb (C).
- The density of electric flux is the electric (displacement) flux density, D.
- It is the measure of cluster of ‘electric lines of force’. It is the number of lines of force per unit area of cross section.
D = ψ / S → ψ = ∫S (D . ds)
ALSO READ:
- Introduction To Electrostatics.
- Coulomb's law.
- Electric Field Intensity (E).
- Electric Lines Of Forces /Streamlines / Electric Flux (ψ) .
- Electric Flux Density (D).
- Electric Field Intensity Due To a Finite and Infinite Line Charge.
- Electric Field Intensity Due To a Infinite Sheet Charge.
- Electric Field Intensity Due To a Circular Ring Charge.
- Electric Field Intensity Due To a Circular Disk Charge.
- Numericals / Solved Examples - Electric Force and Field Intensity.
- Numericals / Solved Examples - Electric Field Intensity - Line, Surface and Mixed Charge Configuration.
- Short Notes/FAQ's
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