Physics topic 2

• Circuit Symbols:
• For charge to flow:

  • Circuit must be closed (no open switches)
  • There must be a source of potential difference (battery/cell)
• Current is the flow of electrical charge
• In a single closed loop, the current has the same value at any point
• The current through a component depends on both the resistance (R) of the component and the potential difference (V) across the component
• The greater the resistance of the component, the smaller the current for a given potential difference across the component
• Resistors:

  • If the resistance is constant, an ohmic conductor, current is directly proportional to the potential difference, resulting in a linear graph
  • Resistance of components like lamps, diodes, thermistors, and LDRs is not constant and changes with current, leading to nonlinear graphs
• Factors affecting resistance:

  • With current: as current increases, resistance increases
  • With temperature: resistance decreases in hotter temperatures for thermistors
  • With length: greater length means more resistance
  • With light: LDR resistance decreases with greater light intensity
  • With voltage: diodes have high resistance in one direction and low in the other
• Series Circuits:

  • Current only follows a single path
  • Total Resistance = R1 + R2 + ...
• Parallel Circuits:

  • Current splits into multiple paths
  • Total resistance for two resistors in parallel is less than the resistance of the smallest resistor
• Mains electricity in the UK is AC with a frequency of 50 Hz and about 230 V
• In a plug, there are 3 wires: Live wire (brown), Neutral wire (blue), and Earth wire (green and yellow stripes)
• Power is directly proportional to current and voltage
• National Grid:

  • System of cables and transformers linking power stations to consumers
  • Transformers change potential difference, step-up for power stations and step-down for consumers
• Static Electricity:

  • Insulators do not conduct electricity
  • Conductors can conduct electricity
  • When two insulators are rubbed together, electrons transfer, creating positive and negative charges