Physics P4

• What is electric current?

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

  Electrons
• What is the unit of current?

  Ampere (amp, A)
• How is 1 ampere defined?

  1 coulomb of charge flow per second
• What is the formula for charge?

  Charge (C) = current (A) x time (s)
• In which direction does conventional current flow?

  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 (p.d.)?

  Measure of energy transferred between two points
• What is the unit of potential difference?

  Volt (V)
• What does the p.d. across a component represent?

  Work done on it by each coulomb of charge
• What does the p.d. 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 is the formula for potential difference?

  Potential difference (V) = energy transferred (J) / charge (C)
• What happens when two objects have a strong electric field between them?

  Electrons in air are attracted, causing a spark
• How can electric fields be represented?

  Using a diagram with field lines
• What do field lines show in an electric field?

  The direction of force on a positive charge
• How should field lines meet the surface of charged objects?

  At 90 degrees
• Which direction do arrows on field lines point?

  Away from positive charges, towards negative charges
• How can insulating materials become charged?

  By rubbing with another insulating material
• What happens to materials that gain electrons?

  They become negatively charged
• What happens to materials that lose electrons?

  They become positively charged
• How is electric charge measured?

  In coulombs (C)
• Why does an atom have no charge?

  It has equal numbers of protons and electrons
• What happens when electrons are removed from an atom?

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

  It becomes negatively charged
• What are the key terms related to electric circuits?

  • Ampere
  • Charge
  • Coulomb
  • Current
  • Electric field
  • Electrostatic force
  • LDR
  • Parallel
  • Potential difference
  • Resistance
  • Series
  • Static
  • Thermistor
• 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 is the relationship between like charges and opposing charges?

  Like charges repel, opposing charges attract
• How does the strength of the electric field change with distance?

  It gets stronger as distance decreases
• What happens when electrons move through a circuit?

  They collide with ions and atoms, causing resistance
• 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 a longer wire
• How can the resistance of an electrical component be found?

  By measuring current and potential difference
• What is the formula for potential difference in terms of current and resistance?

  V = IR
• What is an I-V graph?

  A graph of current against potential difference
• What happens to the temperature of a filament as more current flows through it?

  Its temperature increases
• How does resistance change with temperature in a filament?

  Resistance increases as temperature increases
• How does the resistance of a thermistor change with temperature?

  It decreases as temperature increases