Current, Voltage and Resistance

• Example 2

  • If 24 volt battery produces 8 amps, to find resistance we rearrange equation to r equals v over i and do 24 divided by 8 to give 3 ohms
• Relationship between voltage, current, and resistance

  As long as resistance stays constant, increasing voltage should increase current proportionally or vice versa
• Example 1

  • If circuit has current of 4 amps and resistance of 2 ohms, voltage of cell must be 4 times 2, so 8 volts
• Lines in circuits containing only wires or resistors are straight due to constant resistance
• As potential difference increases

  Current in the circuit would also increase
• Higher currents generally cause wires to heat up
• Smaller resistor requires less potential difference to drive a large current
• Temperature increase

  Resistance would also increase
• Filament lamps contain a thin metal filament that heats up as current flows, increasing resistance
• Equation v equals ir

  Potential difference or voltage equals current times resistance
• v equals ir is probably the most important equation in the electricity topic
• Temperature staying constant is assumed for the straight lines in circuits
• Graphs of filament lamps and diodes
• Diodes only allow current to flow in one direction, showing current when potential difference is positive
• Diodes effectively block current flow in the reverse direction due to high resistance
• Less current can flow per unit of potential difference at higher voltages in filament lamps
• Diodes have high resistance in the reverse direction to prevent current flow
• For different wires or resistors, the line would still be straight but more or less steep
• Temperature and resistance increase in filament lamps as current flows, making the curve less steep