physics

• Electric current


  Charges in motion from one region to another
• Conduction path


  Closed loop where charges follow
• Current (I)


  Any motion of charge from one region to another
• Ways to produce the same current


  • Positive charges moving in the direction of the electric field
  • Same number of negative charges moving at the same speed in the direction opposite to the electric field
• Conventional current


  Treated as a flow of positive charges, regardless of whether the free charges in the conductor are positive, negative, or both
• Current is not a vector
• Current density (J)


  Current per cross-sectional area
• Resistivity


  • The ratio of the magnitudes of electric field and current density
  • Measure of the ability of a material to oppose the flow of the current
• Conductors, insulators, semiconductors

  • Metals are good conductors of electricity, they have low resistivity
  • Insulators like rubbers, glass, graphite, plastics have very high resistivity
  • Semiconductor which comes in between the conductors and insulators
• The greater the resistivity


  The greater the field needed to cause a given current density
• Conductivity (σ)


  • Reciprocal of resistivity
  • Intrinsic property of a material which is defined as the measure of the amount of the electric current a material can carry
• Resistance (R)


  Obstruction to the flow of electric current
• Factors affecting electrical resistance


  • Cross-sectional area of the conductor
  • Length of the conductor
  • Material of the conductor
  • Temperature of the conductor
• Ohm (Ω)


  SI unit of resistance
• The SI unit of energy is the joule (J).
• Energy can be transferred between objects by work done, heating or cooling, and electric current.
• Resistor


  A circuit device made to have a specific value of resistance between its ends
• For a conductor to have a steady current, it must be a part of a path that forms a closed loop or complete circuit
• Electric circuit

  A closed loop or path, forming a network of electrical components where electrons can flow. This path is made using electrical wires and powered by a source, like a battery
• If an electric field is produced inside a conductor that is not a part of a complete circuit current flows for only a very short time
• Electromotive force (emf)


  The influence that makes current flow from lower to higher potential
• Emf


  The energy supplied by a battery or a cell per coulomb of charge
• Emf is not a force but an energy-per-unit-charge quantity
• Source of emf (Ɛ)

  A device that provides emfs. Examples: batteries, solar cells, fuel cells
• Internal resistance

  The resistance between a battery or other voltages sources that causes a drop in the source voltage when there is a current
• For a real source of emf, the terminal voltages equal the emf only if no current is flowing through the source