SP10 - Electricity&Circuits

• An electrical circuit is a closed loop that contains a power source like a cell and something for the electrons to flow through, represented with circuit diagrams
• Common symbols in circuit diagrams:

  • Cell: simple version of a battery
  • Battery: made up of two or more cells
  • Filament lamp: symbol for a small light bulb
  • Switch: can be open or closed to disrupt or allow current flow
• Key terms in circuits:

  • Current (i): measure of electron flow, denoted in amperes (amps)
  • Potential difference (v): force driving electron flow, measured in volts
  • Resistance (r): opposes electron flow, measured in ohms
• In a circuit, current flows from the positive terminal to the negative terminal, following the convention of conventional current where current flows from positive to negative
• In circuits with only wires or resistors, the resistance remains constant, resulting in straight lines on current versus potential difference graphs
• Filament lamps, like light bulbs, show a curve on the graph where the resistance increases as the wire heats up due to the current flow, emitting light
• Diodes allow current flow in one direction, showing current only when the potential difference is positive, with high resistance in the reverse direction to prevent current flow
• Components in an electrical circuit:

  • Battery
  • Switches
  • Voltmeter
  • Ammeter
  • Fixed resistor
  • Variable resistor
  • Filament lamp
  • Motor
  • Diode
  • Thermistor
  • LDR
  • LED
• Purposes of components in an electrical circuit:

  • Battery: provides a potential difference
  • Switches: allows the current flow to be switched on or off
  • Voltmeter: measures potential difference across a component
  • Ammeter: measures the current flowing through a component
  • Fixed resistor: provides a fixed resistance to the flow of current
  • Variable resistor: provides a variable (changeable) resistance
  • Filament lamp: converts electrical energy to light energy as a useful form
  • Motor: converts electrical energy to kinetic energy as a useful form
  • Diode: allows current to flow in one direction only
  • Thermistor: resistance decreases when the temperature increases
  • LDR: resistance decreases when the light intensity increases
  • LED: a diode that gives out light when current flows through it
• An open switch has no connection between its terminals, so there is no flow of electricity
• Electrons flow clockwise in the circuit through the cell, wires, three ammeters, and two resistors
• Components in circuits can be arranged in series or parallel, with different rules for current and potential difference in each type
• Series circuits have just one loop for electric current flow, and the potential difference across components in series must add up to give the cell voltage
• In series circuits, the size of the current is the same at every point in the circuit, and ammeters are always connected in series with components
• Parallel circuits contain more than one loop, and the potential difference across components in each branch must add up to give the cell voltage
• In parallel circuits, the sum of the currents in each branch must equal the current leaving the cell
• Ammeters have very low resistance to accurately measure current, while voltmeters have very high resistance to prevent current flow through them
• Energy, charge, and potential difference are closely related in electrical circuits
• The equation relating energy, charge, and potential difference is: E = Q x V
• To calculate the charge, Q, from the current reading on the ammeter, use the equation Q = I x t
• The potential difference, V, across the bulb is measured with a voltmeter, which is always connected in parallel with components
• An electric current is the rate of flow of charge, with the unit of charge being the coulomb (C) and one ampere (A) equaling one coulomb of charge per second
• To measure the size of the current flowing through a component, an ammeter is connected in series with the component
• In a closed circuit with a source of potential difference, electric current will flow, and the current is the same at all points in a series circuit