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 formula relating 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 determine the current through a component?

  The current through a component 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 of the component, 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, an ohmic conductor has current directly proportional to the potential difference, resulting in a linear graph.
• How does the resistance of components like lamps and diodes change?

  The resistance of components such as lamps and diodes is not constant and changes with the current through the component, resulting in a nonlinear graph.
• How does current affect the resistance in a resistor?

  As current increases, electrons have more energy and collide with atoms in the resistor, causing resistance to increase and current to decrease.
• How does temperature affect resistance in normal wires and thermistors?

  In normal wires, resistance increases with temperature; in thermistors, resistance decreases at higher temperatures.
• 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.
• How does light intensity affect the resistance of an LDR?

  The greater the intensity of light, the lower the resistance of an LDR.
• What happens to the resistance of a diode in different directions of current flow?

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

  The total resistance in a series circuit 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, with the power supply's potential difference equal to the sum of the potential differences across each component.

  
• What characterizes a parallel circuit?

  In a parallel circuit, components are connected separately to the power supply, and the potential difference is the same across all branches.
• How does current behave in a parallel circuit?

  The total current into a junction is equal to the total current in each of the branches.
• What is the total resistance in a parallel circuit?

  The total resistance for two resistors in parallel is less than the resistance of the smallest resistor.
• How do electric fields behave around charges?

  Electric fields point in the direction a positive charge would go, away from positive charges and towards negative charges.
• How does the strength of an electric field relate to the charge?

  The stronger the charge, the more field lines are present and the stronger the force felt.
• What is the National Grid?

  The National Grid is a system of cables and transformers linking power stations to consumers across the UK.
• What is the function 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, decreasing current to reduce energy loss.
• What do step-down transformers do?

  Step-down transformers decrease the potential difference from the National Grid to consumers for safety.
• What is electrical charge?

  A property of all matter that can be positive or negative.
• What happens when a body has equal amounts of positive and negative charge?

  They cancel out, forming a neutral body.
• What is the behavior of like and opposite charges?

  Like charges repel each other, while opposite charges attract.
• What distinguishes insulators from conductors?

  Insulators do not conduct electricity because their electrons cannot flow, while conductors can conduct electricity because their electrons are delocalized and can flow.

  
• What occurs when two insulators are rubbed together?

  Electrons are transferred from one object to the other, forming a positive charge on one object and a negative charge on the other.
• Why do conductors remain neutral when rubbed?


  Electrons will flow in and out of conductors, cancelling out any charge effect, so they stay neutral.
• What causes sparking in static electricity?


  Sparking occurs when enough charge builds up and the objects are close but not touching, causing charge to jump through the air.
• What is the electrostatic force?

  The electrostatic force is the force of attraction or repulsion experienced by charged objects.
• How does the distance between charged objects affect the electrostatic force?

  The closer the objects are, the greater the force felt, as force is proportional to the inverse square of the distance.
• What type of current is mains electricity?

  Mains electricity is an alternating current (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.
• How does alternating current (AC) differ from direct current (DC)?

  AC continuously varies from positive to negative, while DC is the movement of charge in one direction only.
• What are the three wires in a plug and their functions?


  The live wire carries alternating potential difference, the neutral wire completes the circuit, and the earth wire is a safety wire that carries current only if there is a fault.