Current electricity

• The direction of electric current is in the direction opposite to direction of electrons
• Electrons drift in the direction opposite to the electric field
• Acceleration of e (a)= q E/m
• With increase in temperature e K.E. increases so more collision, less relaxation time and decrease in drift velocity hence resistance increases
• Thermal velocity of e, E = 3/2KT
• Resistance is directly proportional to heat energy.
• Bonded e ossilate in their position due to energy acquired during collision. This energy will be released in form of heat
• Resistivity is independent of length and area
• Mobility- drift velocity gain per unit electric field
• Mobility does not depend on electric field
• Slope of resistivity vs temp will be small if high resistivity
• slope of resistivity vs temp will be more if low resistivity
• Electron density is independent of temp
• Temperature coefficient of resistivity is positive for metals
• In alloys atoms are in disorder so alloy have higher resistivity, their disorder due to temp increase become insignificant hence alloys are almost independent of temp
• Value of temp coefficient is negative for semiconductor
• Internal resistance of cell: resistance offered by the electrolyte of the cell
• I.R. cell depends upon:

  1. directly proportional to separation of electrodes
  2. inversely proportional to area of electrodes immersed in electrolyte
  3. inversely proportional to concentration of electrolyte
  4. nature of electrolyte
  5. resistance increases with decrease in temp
• EMF of cell: max potential difference between electrodes of cell in open circuit
• terminal potential: potential difference between electrodes of cell in closed circuit
• Balance condition only possible when BATTERY AND GALVANOMETER CONNECTED AT TWO DIFFERENT TERMINAL
• Galvanometer shows deflection due to current flowing through it, but no current flows into galv.
• Output power of source emf will be max when external resistance is equal to internal resistance