AQA Electricity Topic Summary

Overview

• Electrical circuits contain various small electrical components.
• Circuit symbols are essential for drawing circuits efficiently.
• Important components: power supply (cell), ammeter, lamp, voltmeter.

Basics of Circuits

• Ammeter: measures current, placed in series.
• Voltmeter: measures potential difference, placed in parallel.
• Electric current is the rate of flow of electric charge.
  • Equation: Q = I * T
    • Q: Charge (coulombs)
    • I: Current (amps)
    • T: Time (seconds)

Potential Difference and Resistance

• Ohm's Law: $V = I \times R$
  • $V$: Potential difference (volts)
  • $R$: Resistance (ohms)
  • $I$: Current (amps)
• Characteristics of different components:
  • Resistor: Ohmic conductor, linear relationship (current ∝ potential difference)
  • Filament Lamp: Non-ohmic, resistance increases with temperature.
  • Diode: Current flows in one direction, operates like a one-way valve.

Special Components

• Light Dependent Resistor (LDR): Resistance decreases with light intensity.
• Thermistor: Resistance decreases with temperature increase.

Types of Circuits

• Series Circuits: Components are arranged one after another.
  • Same current throughout: $I_1 = I_2 = I_3$
  • Total resistance: $R_{total} = R_1 + R_2$
• Parallel Circuits: Components are arranged in separate loops.
  • Current splits: $I_1 = I_2 + I_3$
  • Same potential difference across loops: $V_1 = V_2 = V_3$
  • Total resistance is less than individual resistances.

Electrical Power and Energy Transfer

• Power (P): Rate of energy transfer.
  • Equation: $P = V \times I$
    • $P$: Power (watts)
    • $V$: Potential difference (volts)
    • $I$: Current (amps)
• Alternative power equation: $P = I^2 \times R$
• Energy equations: $E = P \times T$ and $E = Q \times V$

Alternating Current (AC) and Direct Current (DC)

• Direct Current (DC): Flows in one direction.
• Alternating Current (AC): Current direction changes cyclically.
  • UK mains supply: 230V, 50Hz
  • Household wiring includes live, neutral, and earth wires for safety.
  • National Grid: Transfers energy over large distances.
    • Transformers: Step-up (increase voltage, decrease current), Step-down (decrease voltage)

Static Electricity

• Electrostatics: Charge transfer via friction.
  • Objects can become positively or negatively charged.
  • Opposite charges attract; like charges repel.
• Electric Field: Region around a charged object where forces are exerted on other charges.
  • Field lines point in the direction a positive test charge would move.