electric current resistance

• Chemical battery


  A device that converts chemical potential energy into electrical energy
• Electrical circuit

  Any complete loop consisting of wires and electrical devices
• Anode


  The positive terminal of a battery
• Cathode


  The negative terminal of a battery
• Electric current


  The net rate at which charge flows past a given point
• Direct current (DC)

  In a battery circuit, the electrons can only flow in one direction, from negative terminal to positive terminal
• Electromotive force (EMF)


  The potential difference across the two terminals of a battery (or any DC power supply) when not connected to an external circuit
• Terminal voltage


  The voltage across a battery or power supply when it is connected to an external circuit
• How a simple chemical battery works

  1. Two electrodes (different metal strips) in an electrolyte (solution that conducts electricity)

  2. The different metals dissolve at different rates in the acid

  3. As the metals dissolve, their atoms move into solution as positively charged ions, leaving behind electrons

  4. Both electrodes accumulate excess electrons, but one will have a larger excess

  5. The cathode becomes more negatively charged than the anode

  6. The anode is at a higher potential than the cathode
• How a simple chemical battery works (continued)


  1. The potential difference across the electrodes can cause electrons to flow in the wire

  2. The voltage causes current, or flow of charge, in the wire

  3. There is also a current in the solution as the positive ions migrate, so the circuit is complete

  4. Over time, as electrode A continues to receive more electrons than normal, it attracts A ions from solution

  5. A ions reattach to electrons to form neutral atoms and deposit on the A electrode

  6. In the meantime, B is slowly dissolving

  7. The chemical potential energy is converted to light and heat in the lightbulb
• When batteries are connected in series

  Their voltages add and the voltage across the resistance R is the sum of the voltages
• When batteries of the same voltage are connected in parallel


  The voltage across the resistance is the same, as if only a single battery were present
• Complete circuit


  A battery or some other source connected to a continuous conducting path
• Conventional current


  The direction in which positive charge would move
• Electric current (I)


  The time rate of flow of net charge
• Drift velocity


  The average velocity of the electron flow in a metal wire
• Factors that influence resistance

  • Type of material
  • Length (L)
  • Cross-sectional area (A)
  • Temperature (T)
• Resistivity (ρ)


  Determined by the resistive properties of a material (partly due to intrinsic atomic properties)
• Conductivity (σ)


  The inverse of resistivity
• For an ohmic resistor, current and resistance


  Are directly proportional
• Power (P)


  The rate at which energy is used