Electric Current

• Current= flow of electrons (I)
• in metals the charge carries are conducting electrons the move around in the metal colliding with each other and fixed ions
• in salts the charged is carried by ions

   Q=I  t

• P.D or Voltage=the work done per unit charge

  V=W/Q

• The emf of a source of electricity is defined as the electrical energy produced per unit charge passing throught the source

W(work done)=IV  t
power=IV

• Resistance= the pd of a component /the current through it

R=V/I

• an ammeter is used to measure current and is connecred in seris
• a voltmeter is used to measure the PD and is connected in parralel to the resistor
• a variable resistor can be used to adjust the current and P.D
• Ohms law stated that the pd across a metallic conducto is proportianal to the curren through ***, providing the physical condition does not change
• on a graph where voltage (y) is plotted against current (x) the resistance isthe gradient

Resistivity(   )=RA/L
r=d/2, a= Πr²

• Superconductivity=a wire or deice made of a material which has zero resistance at and below a critical temperature( this depends on the material) if the temperatire is raised then the superconductivity is lost the boiling point of liquid nitrogen is called a high-temperature superconductor, superconductours are used to make high-power electromagnets that generate strong magnetic fields without waisting energy

• Tempratue= resistance increases with temperature as positive ions vibrate moe which makes it harder for the current to pass it is called Positive temperatue coefficent