P6

• Current - is any motion of charge from one region to another
• Conventional current - is treated as a flow of positive charges, regaardles o whether the free charges in the conductor are positive, negative or both.
• Ampere (A)- SI unit for current
• Current is not a vector
• Definition of current - I=Q/t
• Electric circuit - the charges follow a conducting path that forms a close loop
• Current density (J)- current per cross-sectional area
• Formula for current density - J=I/A
• Resistivity (p) - is the ratio of the magnitude of electric field and current density.
• Current density


  Electric current per cross-sectional area
• Resistivity


  The ratio of the magnitudes of electric field and current density. It is the measure of the ability of a material to oppose the flow of current.
• Metals are good conductors of electricity. Hence, they have low resistivity.
• Insulators like rubber, glass, graphite, plastics, etc. have very high resistivity when compared to the metallic conductors.
• Semiconductors


  Come in between the conductors and insulators. Their resistivity decreases with the increase in temperature and is also affected by the presence of impurities in them.
• The greater the resistivity, the greater the field needed to cause a given current density.
• The SI unit of resistivity is Ohm-meter (Ω·m).
• Conductors


  • Silver
  • Copper
  • Gold
  • Aluminum
  • Tungsten
• 
  

  Conductivity (o)- reciprocal of resistivity. It is an intrinsic property of a material which is defined as the measure of the amount of electrical current a material can carry.
• Definition of conductivity


  σ = current density / E, where σ = conductivity, E = electric field
• Resistance

  Obstruction to the flow of electric current, denoted by R. Every material has a resistance, which is why conductors give out heat when current passes through.
• Resistance


  The measure of opposition applied by any object to the flow of electric current
• Resistance


  The ratio of V (voltage) to I (current) for a particular conductor
• Ohm(Ω) - SI unit for Resistance
• Resistor - a circuit device made to have a specific value of resistance between its ends
• Electric circuit - is a close loop or path , forming a network of electrical components where electrons can flow
• Electromotive force (emf)- the influence that makes current flow from lower to higher potential.
• Source of emf (٤)- a device that provides emf. Examples are batteries, electric generators, solar cells, thermocouples, fuel cells
• Internal resistance - the resistance within a battery or other voltage sources that causes a drop in the source voltage when there is a current