Electricity

• What must be true for electrical charge to flow in a circuit?

  The circuit must be closed and there must be a source of potential difference.
• What is electrical current?

  Current is the flow of electrical charge.
• How does the rate of flow of charge relate to current?

  The greater the rate of flow of charge, the greater the current.
• What is the equation that relates charge flow, current, and time?

  $Q =$$I \cdot t$
• What happens to the current in a single closed loop?

  The current has the same value at any point in the loop.
• What factors affect the current through a component?

  The current depends on both the resistance of the component and the potential difference across it.
• How does resistance affect current for a given potential difference?

  The greater the resistance, the smaller the current for a given potential difference.
• What is the equation that relates potential difference, current, and resistance?

  $V =$$I \cdot R$
• What characterizes an ohmic conductor?

  If the resistance is constant, the current is directly proportional to the potential difference, resulting in a linear graph.
• How does the resistance of components like lamps and diodes change with current?

  The resistance changes with the current, resulting in a nonlinear graph.
• What happens to the resistance of a filament lamp as its temperature increases?

  The resistance of a filament lamp increases as the temperature of the filament increases.
• How does current affect resistance in a resistor?

  As current increases, electrons gain more energy and collide with atoms, increasing resistance.
• How does temperature affect resistance in normal wires?

  As temperature increases, the resistance also increases due to increased atomic vibration.
• What is the behavior of a thermistor with temperature changes?

  In hotter temperatures, the resistance of a thermistor is lower.
• How does the length of a wire affect its resistance?

  The greater the length of the wire, the more resistance and the lower the current.
• What is the relationship between light intensity and the resistance of an LDR?

  The greater the intensity of light, the lower the resistance of an LDR.
• What happens to the resistance of an LDR in the dark?

  The resistance is greatest when it is dark.
• How does a diode behave in terms of current flow?

  A diode allows current to flow freely in one direction and has high resistance in the opposite direction.
• What is the total resistance in a series circuit?

  Total resistance is the sum of the resistance in each component.
• How does current behave in a series circuit?

  The current is the same everywhere in a series circuit.
• What is the potential difference in a series circuit?

  The potential difference is shared across the whole circuit.
• How are components connected in a parallel circuit?

  Components are connected separately to the power supply in a parallel circuit.
• What happens to the current in a parallel circuit?

  The current splits into multiple paths in a parallel circuit.
• How does potential difference behave in a parallel circuit?

  The potential difference is the same across each branch in a parallel circuit.
• What is the total current in a parallel circuit?

  The total current into a junction equals the total current in each of the branches.
• How does the total resistance in a parallel circuit compare to the smallest resistor?

  The total resistance for two resistors in parallel is less than the resistance of the smallest resistor.
• What type of electricity supply is mains electricity?

  Mains electricity is an AC supply.
• What is the frequency and voltage of the domestic electricity supply in the UK?

  The frequency is 50 Hz and the voltage is about 230 V.
• What is the difference between AC and DC?

  AC is alternating current, which continuously varies, while DC is direct current, which moves in one direction only.
• What are the three wires in a plug?

  Live wire, neutral wire, and earth wire.
• What is the function of the live wire in a plug?

  The live wire carries the alternating potential difference from the supply.
• What is the function of the neutral wire in a plug?

  The neutral wire completes the circuit.
• What is the function of the earth wire in a plug?

  The earth wire is a safety wire that carries current only if there is a fault.
• What is power in terms of energy transfer?

  Power is the energy transferred per second.
• How is power related to current and voltage?

  Power is directly proportional to current and voltage.
• What is the equation for energy transferred in terms of power and time?

  $E =$$P \cdot t$
• What is the equation for energy transferred in terms of charge and potential difference?

  $E =$$Q \cdot V$
• What is the role of the National Grid?

  The National Grid links power stations to consumers across the UK.
• What do transformers do in the National Grid?

  Transformers change the potential difference for efficient power transfer.
• What is the function of a step-up transformer?

  A step-up transformer increases the potential difference from the power station to the National Grid.