Energy, power and resistance.

• Potential difference = measure of the transfer of energy by charge carriers
• One volt = when 1J of energy is transferred per unit charge passing through the component
• EMF = when work is done on charge carriers. These carriers gain energy as they pass through a cell. More emf = more electrical energy
• Energy transferred = VQ /EMFQ
• Electron gun:

  filament is heated by current which releases an electron. If heated filament is in a vacuum, it turns to a cathode, accelerating the e- thermionic emission

  Goes towards an anode with small holes in it which releases them at a specific kinetic energy.
• eV =1/2mv^2
• Ohm’s law = when a metallic conductor is at a constant temperature, the current is directly proportional to the potential difference
• When temps increase, resistance increases as more kinetic energy and more collisions so more charge carriers have to do more work
• Filament lamp is non-ohmic. It increases with voltage. This is due to filament getting warm . More current is inputted so more collisions
• Resistivity = the electrical property of a material
• To determine the resistivity of a material:

  See how resistance varies when length changes.

  calculate resistance through V/I

  Length is directly proportional to resistance

  Plot a graph of R agsinst L which is straight

  Y=mx + c. As R = pL/A the gradient is p/A so p = gradient x a

  
• Some semi conductors‘ resistance drops as temperatures increase. This is due to the number density of charge carriers increases too
• Investigating thermistors:

  Heat up thermistor whilst measuring voltage and current
• LDR increases the resistance of a circuit when light is not present. This is due to there being less charge carriers so higher resistance