Electric flux

9. Electric Flux

• Consider a plane surface of area ΔS in a uniform electric field E in the space.
  
  
• Draw a positive normal to the surface and θ be the angle between electric field E and the normal to the plane.
  
  
  
  
• Electric flux of the electric field through the choosen surface is then
  Δφ = E ΔS cosθ
  
  
• Corresponding to area ΔS we can define an area vector ΔS of magnitude ΔS along the positive normal. With this definition one can write electric flux as
  Δφ = E . ΔS
  
  
• direction of area vector is always along normal to the surface being choosen.
  
  
• Thus electric flux is a measure of lines of forces passing through the surface held in the electric field.
  
  Special Cases
  
• If E is perpendicular to the surface i. e., parallel to the area vector then θ = 0 and
  Δφ = E ΔS cos0
  
  
• If θ = π i. e., electric field vector is in the direction opposite to area vector then
  Δφ = - E ΔS
  
  
• If electric field and area vector are perpendicular to each other then θ = π/2 and Δφ = 0
  
  
• Flux is an scaler quantity and it can be added using rules of scaler addition.
  
  
• For calculating total flux through any given surface , divide the surface into small area elements. Calculate the flux at each area element and add them up.
  
  
• Thus total flux φ through a surface S is
  φ ≅ ΣE.ΔS
  
  
• This quantity is mathematically exact only when you take the limit ΔS→0 and the sum in equation 3 is written as integral
  φ = ∫ΣE.dS
  

• Notes
  • Electric Charge , Basic properties of electric charge and Frictional Electricity
  • Electrical and electrostatic force
  • Coulomb's Law (with vector form)
  • Principle Of Superposition
  • Electric Field & Calculation of Electric Field
  • Electric Field Lines
  • Electric Flux
  • Electric Dipole and Dipole Moment
  • Electric Dipole Field
• Assignment
  • Electrostatics Multiple Choice Questions
  • Electrostatics Problems
  • Electrostatics Questions and answers
  • Electrostatics Important Questions for Class 12