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• Direction of current flow in a circuit

  Electrons flow from the negative terminal to the positive terminal, but conventionally current is considered to flow from the positive terminal to the negative terminal
• What an electrical circuit is

  A closed loop that contains a power source such as a cell and something for the electrons to flow through like a wire
• A simple electrical circuit contains a power source and something for the electrons to flow through
• For exams, current is considered to flow from the positive terminal to the negative terminal
• A filament lamp is symbolized by a small light bulb in circuit diagrams
• A switch in a circuit can be closed to allow current to flow or open to disrupt the circuit
• Potential difference (denoted by v) is the force driving the flow of electrons and is provided by the cell or battery, measured in volts
• Current (denoted by i) is a measure of the flow of electrons around the circuit, similar to the flow of water through a pipe, and is measured in amperes (amps)
• Cells and batteries act in the same way in circuits
• Representation of electrical circuits

  • Generally represented with circuit diagrams
• Resistance (denoted by r) opposes the flow of electrons, similar to a partial blockage in a pipe, and is measured in ohms
• Key terms in circuits

  • Potential difference, current, resistance
• Effect of potential difference on current

  Increasing potential difference leads to increased current in the circuit
• Example 2

  • 24 volt battery producing a current of 8 amps, resistance is three ohms
• Temperature increase leads to an increase in resistance
• Temperature stability assumption is made for the straightness of the lines in the graphs
• Diodes only allow current to flow in one direction, showing current when potential difference is positive
• Equation v equals ir

  Potential difference or voltage equals current times resistance
• In circuits containing only wires or resistors, the resistance stays constant
• Relationship between voltage, current, and resistance

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

  • Circuit with current of four amps and resistance of two ohms, voltage of cell is eight volts
• Effect of resistance on graph lines

  Resistance affects the steepness of the graph lines
• Graphs of filament lamps show less steep curves as current increases due to increased resistance from heat
• Higher currents generally cause wires to heat up, affecting the resistance
• Diodes have high resistance in the reverse direction to prevent current flow
• Example 1

  • Kettle draws a current of 12 amps and takes 50 seconds to boil. How much charge passed through the wire? Solution: 12 x 50 = 600 coulombs
• Charge


  Represented by the letter q and measured in coulombs (c)
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• Current is like

  The rate at which water is flowing through a river
• Example 2

  • Phone charger transfers a total charge of 43.2 kilo coulombs over a period of two hours. What current flowed through the wire? Solution: 43.2 x 1000 / (2 x 60 x 60) = 6 amps
• Definition of charge

  Measure of the total current that flowed within a certain period of time
• Charge is like

  The total amount of water that's flowed down the hill within a certain period of time
• Equation for charge

  Charge = Current (measured in amps) x Time (measured in seconds)