Electricity

• Current is the flow of electrical charge
• The current through a component depends on resistance and p.d.
• What happens to the current when resistance increases?

  It decreases
• Charge flows from positive to negative
• If resistance is constant, current is directly proportional to p.d.
• Energy is supplied to electrons from a battery
• Current flows through a diode in one direction only
• P.d. measures how much energy is transferred from one point
• What happens to the resistance of a filament lamp as temperature increases?

  It increases
• What happens to electrons as they flow through a resistor?

  They collide with atoms
• In parallel circuits, components can be switched independently because current is shared
• What happens to the resistance of a thermistor as temperature increases?

  It decreases
• In an L.D.R., resistance decreases as light intensity increases
• The National Grid uses a frequency of 50 Hz and a voltage of 230 V.
• What is the difference between AC and DC current?

  AC varies, DC is unidirectional
• Match the three wires in a cable with their function:

  Live wire ↔️ Carries current

  Neutral wire ↔️ Completes circuit

  Earth wire ↔️ Carries fault current
• Step-up transformers increase p.d. to reduce energy loss through friction
• What is the fundamental principle behind charged objects attracting or repelling each other?

  Coulomb's law
• Electric field lines move from positive to negative
• What is power defined as in terms of energy and time?

  Energy transferred per second
• A higher power rating indicates that an appliance uses more energy