Electricity

• What is electric current measured in?

  Amperes (A)
• How is electric current defined?

  It is the rate of flow of electric charge through a conductor.
• If a charge of $10 \text{ C}$ flows in $5 \text{ s}$, what is the current?


  $I =$$\frac{Q}{t} =$$\frac{10 \text{ C}}{5 \text{ s}} =$$2 \text{ A}$
• What is conventional current?

  It flows from the positive terminal to the negative terminal of the power source.
• What is the actual movement of electrons in a circuit called?

  Electron flow.
• What is voltage measured in?

  Volts (V)
• What does voltage represent in a circuit?

  It is the potential difference that drives the current.
• If $10 \text{ J}$ of energy is transferred with a charge of $2 \text{ C}$, what is the voltage?


  $V =$$\frac{E}{Q} =$$\frac{10 \text{ J}}{2 \text{ C}} =$$5 \text{ V}$
• What is resistance measured in?

  Ohms (Ω)
• What does resistance oppose in a conductor?

  It opposes the flow of current.
• How does resistance change with the length of a wire?

  Resistance increases with longer wires.
• What happens to resistance as the temperature increases in many materials?

  Resistance increases with temperature.
• What is Ohm's Law?

  It states that voltage is directly proportional to current for a conductor at constant temperature.
• What does a graph of current versus voltage look like for an ohmic conductor?

  It is a straight line.
• What are the characteristics of a series circuit?

  • Components are connected end-to-end.
  • Current is the same through all components.
  • Total voltage is shared between components.
  • Total resistance is the sum of individual resistances.
• What are the characteristics of a parallel circuit?

  • Components are connected with multiple paths.
  • Current splits between branches.
  • Voltage is the same across all branches.
  • Total resistance decreases as more branches are added.
• What is electrical power measured in?

  Watts (W)
• How is electrical power calculated?

  Power is the product of voltage and current.
• If the voltage is $5 \text{ V}$ and the current is $2 \text{ A}$, what is the power?


  $P =$$VI =$$5 \text{ V} \times 2 \text{ A} =$$10 \text{ W}$
• What is the formula for energy transferred in a circuit?

  Energy is the product of power and time.
• If the power is $20 \text{ W}$ and the time is $3 \text{ s}$, what is the energy transferred?


  $E =$$Pt =$$20 \text{ W} \times 3 \text{ s} =$$60 \text{ J}$
• What are the safety devices used in electrical systems?

  • Fuses: Melt to break the circuit when current exceeds a limit.
  • Circuit Breakers: Automatically break the circuit if current exceeds a value.
  • Earthing: Connects appliances to the ground for safety.
  • Double Insulation: Plastic casings prevent appliances from becoming live.
• What is Direct Current (DC)?

  Current that flows in one direction only.
• What is Alternating Current (AC)?

  Current that changes direction periodically.
• What is the frequency of mains electricity in the UK?

  50 Hz
• What are the three wires in a mains electricity circuit?

  Live wire, neutral wire, and earth wire.
• What are the current-voltage characteristics of different components?

  • Ohmic Conductor: Straight line graph, obeys Ohm's Law.
  • Filament Lamp: Curved graph, resistance increases with current.
  • Diode: Allows current in one direction, high resistance in reverse.
• How does resistance behave in series and parallel configurations?

  • Series: Total resistance increases as resistors are added.
  • Parallel: Total resistance decreases as resistors are added.
• How is charge measured?

  In coulombs (C)
• How can charge be calculated?

  Charge is the product of current and time.
• If the current is $3 \text{ A}$ and the time is $4 \text{ s}$, what is the charge?


  $Q =$$It =$$3 \text{ A} \times 4 \text{ s} =$$12 \text{ C}$
• What are practical applications of electricity?

  • Electric Heating: Resistors convert electrical energy into heat.
  • Lighting: Bulbs convert electrical energy into light.
  • Electric Motors: Convert electrical energy into mechanical energy.