Topic 2

• 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 formula relating charge flow, current, and time?

  $Q =$$I \cdot t$
• What is true about 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.
• 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 resistance as current increases in a resistor?

  Resistance increases as current increases due to collisions with atoms.
• How does temperature affect resistance in normal wires?

  As temperature increases, resistance increases due to increased atomic vibrations.
• 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, the more resistance and the lower the current.
• What is the relationship between light intensity and resistance in an LDR?

  The greater the intensity of light, the lower the resistance in an LDR.
• What happens to the resistance of a diode in the reverse direction?

  A diode has a very high resistance in the reverse direction, preventing current flow.
• 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.
• 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 potential difference behave in a parallel circuit?

  The potential difference is the same across each branch in a parallel circuit.
• What is the total resistance for two resistors in parallel?

  The total resistance for two resistors in parallel is less than the resistance of the smallest resistor.
• What type of electricity 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, while DC is direct current.
• What are the three wires in a plug and their functions?

  Live wire carries potential difference, neutral wire completes the circuit, and earth wire is a safety wire.
• What is the danger of the live wire in a plug?

  The live wire may still carry current even if the mains circuit is off.
• What is the purpose of the earth wire?

  The earth wire prevents the appliance from becoming live in case of a fault.
• What is power in electrical terms?

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

  Power loss is proportional to resistance and to the square of the current.
• What is the formula for energy transferred in terms of power and time?

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

  $E =$$Q \cdot V$
• What are the different ways electrical energy can be transferred by appliances?

  Electrical energy can be transferred as kinetic energy, thermal energy, or work done.
• What does the power rating of an appliance indicate?

  The power rating shows the power it uses in watts; a greater power rating means it uses more energy.
• What is the National Grid?

  The National Grid is a system of cables and transformers linking power stations to consumers.
• What is the role of transformers in the National Grid?

  Transformers change the potential difference for efficient power transfer.
• What do step-up transformers do?

  Step-up transformers increase the potential difference from the power station to the National Grid.
• What do step-down transformers do?

  Step-down transformers decrease the potential difference from the National Grid to consumers.
• What is charge in terms of electrical properties?

  Charge is a property of all matter, existing as positive and negative charges.
• What happens when a body has equal positive and negative charges?

  They cancel out, forming a neutral body.