electricity

• An electric field is a region of space in which an electric charge “feels” a force
• Electric field strength at a point is defined as:

  The electrostatic force per unit positive charge acting on a stationary point charge at that point
• • Electric field strength can be calculated using the equation: E=F/Q
• Where:

  • E = electric field strength (N C-1)
  • F = electrostatic force on the charge (N)
  • Q = charge (C)
• The electric field strength is a vector quantity, it is always directed:

  • Away from a positive charge
  • Towards a negative charge
• SI unit of electric field strength= N C-1
• SI unit for force= N or Newtons
• For electro static force on charge= F=QE
• For charge= Q=F/E
• Electric current is defined as the rate of flow of positive charge carriers

  • It is measured in units of amperes (A) or amps
  • The symbol for current is I
• The charge, current and time are related by the equation: I=delta Q/delta T
• Where:

  • I = current (A)
  • ΔQ = change in charge (Q)
  • Δt = time interval (s)
• • Ammeters should always be connected in series with the part of the circuit you wish to measure the current through
• Voltmeters should always be connected in parallel with the part of the circuit you wish to measure the voltage across.
• Although electric charge can be positive or negative, since the conventional direction of current is the flow of positive charge the current should always be a positive value for your exam answers.
• Electric Charge is a property certain particles have. It can either be:

  • A positive charge (+) (eg. proton)
  • A negative charge (–) (eg. electron)
  • A neutral (no) charge (eg. neutron)
• An atom is neutral. This is because it has an equal number of protons (positive charge) and electrons (negative) charge
• However, just the nucleus which is made up of protons and neutrons is positively charged
• In physics, the charge is represented by the symbol Q or q
• The Coulomb

  • The unit of charge is the Coulomb (C)
  • This is defined as the quantity of charge that passes a fixed point per second when a current of 1 A is flowing
  • The coulomb (C), in SI base units, is equal to the quantity of electricity conveyed in one second by a current of one ampere i.e. 1 C = 1 A s