Electricity

• Electrical current is the rate of flow of electrical charge
• Electricity is a form of energy that is produced by moving charged particles around in a circuit.
• Electrical charge will only flow around a complete (closed) circuit is there is a potential difference
• A current can only flow if there's a source of potential difference
• Current is measured in amperes (A)
• In a single, closed loop (like the one on the right) the current has the same value everywhere in the circuit
• Potential difference is also known as voltage
• Potential difference is the driving force that pushes the charge around
• Potential difference is measured in volts (V)
• Resistance is anything that slows down the flow
• Resistance is measured in ohms (Ω)
• The current flowing through a component depends on the potential difference across it and the resistance of the component
• The greater the resistance across a component, the smaller the current that flows (for a given potential difference across the component)
• Total charge through a circuit depends on current and time
• The size of the current is the rate of flow of charge
• Charge flow = current x time
• Charge flow is measured in coulombs
• Time is measured in seconds
• More charge passes through around the circuit when a larger current flows
• V = IR
• Potential difference = current x resistance
• The resistance of a circuit can depend on a number of factors, like whether components are in series or parallel, or the length of wire used in circuit.
• Ammeters measure the current (in amps) flowing through the test wire
• Ammeters must always be places in series with whatever's being investigated
• Voltmeters measure the potential difference across the test wire (in volts)
• Voltmeters must always be placed in parallel around whatever's being investigated, not around nay other bit of the circuit
• Ohmic conductors have a constant resistance
• The resistance of ohmic conductors doesn't change with the current. At a constant temperature, the current flowing through an ohmic conductor is directly proportional to the potential difference across it