electricity

• The equation v = ir is important in the electricity topic
• v = ir stands for potential difference or voltage equals current times resistance
• In a circuit with a current of 4 amps and a resistance of 2 ohms, the voltage of the cell must be 8 volts (4 x 2)
• If a 24 volt battery produces a current of 8 amps, the resistance can be found using r = v / i, giving 3 ohms (24 / 8)
• Relationship between voltage, current, and resistance:

  • As long as resistance is constant, increasing voltage will increase current proportionally, and vice versa
• In circuits with only wires or resistors, the resistance stays constant, resulting in straight lines on current versus potential difference graphs
• Different resistors will result in different slopes on the graph, with bigger resistors having less steep lines and smaller resistors having steeper lines
• Temperature affects resistance, with higher temperatures increasing resistance
• Filament lamps:

  • Contains a thin metal filament that emits light when heated by current flow
  • Resistance increases as the wire heats up, resulting in a less steep curve on the graph
• Diodes:

  • Allow current to flow in one direction only
  • Show current only when potential difference is positive
  • Have high resistance in the reverse direction to prevent current flow
• Charge is a measure of the total current that flowed within a certain period of time
• In the water analogy, current is the rate at which water is flowing through the river, while charge is the total amount of water that's flowed down the hill within a certain period of time
• Charge is represented by the letter q and is measured in coulombs (C)
• The equation to find charge is: charge = current (measured in amps) x time (measured in seconds)
• Example: A kettle draws a current of 12 amps and takes 50 seconds to boil. The total charge passed through the wire is 600 coulombs (12 x 50)
• Example: A phone charger transfers a total charge of 43.2 kilo coulombs over a period of two hours. The current that flowed through the wire is 6 amps (43,200 / 7,200)
• In a series circuit, components are all connected in a single loop
• If any component is disconnected or broken, the whole circuit will stop working
• The potential difference of the cell or battery is shared across all components in a series circuit
• The total voltage in a series circuit is equal to the sum of the voltages across all individual components
• Current is the same everywhere in a series circuit
• We measure current using an ammeter placed in series within the main loop
• The total resistance in a series circuit is the sum of the individual resistances of each component
• To calculate current in a series circuit, divide the total potential difference by the total resistance
• Ammeters generally have tiny resistances that can be ignored in calculations
• To calculate the voltage across a single component in a series circuit, use Ohm's Law: V = I * R
• Components with greater resistance will have a higher share of the voltage in a series circuit
• Parallel circuits have more than one loop, with each loop containing a single component
• Parallel circuits are more useful than series circuits
• If a component breaks in a parallel circuit, the overall circuit remains intact
• All components in truly parallel circuits get their full source potential difference
• Current is shared between all loops in a parallel circuit
• If a circuit with two loops has a total of 4 amps flowing through it, the current can be split unevenly or equally between the loops
• The total current in a parallel circuit is the sum of the currents in each loop
• The way current splits depends on the resistance of individual components, with loops of greater resistance taking a lower share of the current
• The more components added in parallel, the lower the total resistance of the circuit becomes
• Adding more loops in parallel decreases the overall resistance, even if those loops contain high resistance components
• To draw circuit diagrams, we need to know the different components and their symbols
• To provide electric power to a circuit, we need either a cell or a battery
• To control the flow of electricity, we can add a switch that can be closed to allow electricity to flow or open to turn off the circuit