electric circuits

• What is the charge of an atom?

  It has no charge.
• What happens when electrons are removed from an atom?

  It becomes positively charged.
• What occurs when electrons are added to an atom?

  It becomes negatively charged.
• How can insulating materials become charged?

  By rubbing with another insulating material.
• Why do materials gain or lose charge when rubbed together?

  Electrons are transferred between materials.
• What charge do materials that gain electrons have?

  They become negatively charged.
• What charge do materials that lose electrons have?

  They become positively charged.
• Do positive charges usually transfer between materials?

  No, they do not usually transfer.
• What does a charged object create around itself?

  An electric field.
• What happens when a charged object is placed in another charged object's electric field?

  It experiences electrostatic force.
• What do like charges do to each other?

  They repel each other.
• What do opposite charges do to each other?

  They attract each other.
• How does the strength of the electric field change with distance?

  It gets stronger as distance decreases.
• What happens if two objects have a very strong electric field between them?

  Electrons in air are attracted to the positive object.
• What occurs if the electric field is strong enough between two objects?

  Electrons flow between the two objects.
• What is electric current?

  When charge flows.
• What carries the charge in an electric circuit?

  Electrons.
• What is the unit of current?

  Amp (A).
• In circuit diagrams, where does current flow from?

  From positive to negative terminal.
• What is known as conventional current?

  Current flows from positive to negative terminal.
• What is true about current in a single closed loop?

  It has the same value at any point.
• Why are metals good conductors of electricity?

  They contain delocalised electrons.
• What is potential difference?

  Energy transferred between two points.
• What is the unit of potential difference?

  Volt (V).
• What does the potential difference across a component represent?

  Work done on each coulomb of charge.
• What does the potential difference across a power supply represent?

  Energy transferred to each coulomb of charge.
• What is required for electrical charge to flow through a circuit?

  A source of potential difference.
• What happens when electrons move through a circuit?

  They collide with ions and atoms.
• What is the unit of resistance?

  Ohm (Ω).
• Why does a long wire have more resistance than a short wire?

  Electrons collide with more ions in longer wire.
• What is the relationship between current and potential difference in an ohmic conductor?

  • Current is directly proportional to potential difference.
  • Resistance is constant.
  • Graph shape is a straight line through (0,0).
• How does a diode behave in a circuit?

  • Current flows only in one direction (forward).
  • Requires a minimum voltage to flow.
  • Graph shape is a straight line until (0,0), then curves.
• What happens to a filament lamp as current increases?

  • Temperature increases.
  • Atoms vibrate more.
  • Resistance increases with temperature.
  • Graph shape is 's' shaped.
• What are the characteristics of a series circuit?

  • Components connected in a single loop.
  • If one component fails, the whole circuit stops.
  • Higher resistance components transfer larger share of total p.d.
• What are the characteristics of a parallel circuit?

  • Made up of two or more loops.
  • If one branch fails, others remain unaffected.
  • Total resistance is less than the smallest branch.
  • Adding loops allows more current to flow.
• How does adding resistors in parallel affect total resistance?

  • Total resistance decreases.
  • Provides additional routes for current.
  • More current can flow even if p.d. remains unchanged.