2.1 Basic properties of electric charge

  Electrostatics

• Charge is invariant: It is independent of frame of reference.
  
  
• Charge is transferable: Process of charge transfer is called conduction.
  
  
• Charge is a scalar quantity and can be of two types (i.e. $+ve$ or $-ve$). It is added algebraically.
  
  
• Charge is conserved. During any chemical, nuclear, decay etc, the net electric charge of an isolated system remains constant.
  
  
• Current is known as the drift of charge per unit time. So, the charge is expressed as, $$q=It$$
  
  
• The SI unit for measuring the magnitude of an electric charge is the coulomb $(C)$.
  
  
• If a charge of $1$ coulomb drift per second through an unit cross-section of conductor then the current flowing is called as $1$ ampere.
  
  
• Charge is quantized: Robert Millikan discovered that electric charge always occurs as some integral multiple of fundamental unit of charge $(e)$.
  $$q=ne$$ where $n$ is an integer and it corresponds to the number of electrons.
  
  
• Charge on a body can never be $\left( {\frac{1}{3}} \right)e$, $\left( {\frac{2}{3}} \right)e$ etc as it is due to transfer of electron.
  
  
• Charge is always associated with mass. i.e. charge cannot exist without mass. However mass can exist without charge.
  
  
• When charge particle is at rest it produces only electric field.
  
  
• When charged particle is accelerated it produces electric field $+$ magnetic field $+$ radiate energy.