Homework

• What is electric current?


  Electric current is when charge flows.
• What carries the charge in an electric circuit?


  The charge in an electric circuit is carried by electrons.
• What is the unit of current?


  The unit of current is the ampere (amp, A).
• How is 1 ampere defined?


  1 ampere = 1 coulomb of charge flow per second.
• How can you calculate charge using current and time?


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


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


  In a single closed loop, the current has the same value at any point in the circuit.
• Why are metals good conductors of electricity?


  Metals are good conductors because they contain delocalised electrons, which are free to flow.
• What is potential difference (p.d.)?


  Potential difference is a measure of how much energy is transferred between two points in a circuit.
• What is the unit of potential difference?


  The unit of potential difference is the volt (V).
• What does the p.d. across a component represent?


  The p.d. across a component is the work done on it by each coulomb of charge that passes through it.
• What does the p.d. across a power supply represent?


  The p.d. across a power supply is the energy transferred to each coulomb of charge that passes through it.
• What is required for electrical charge to flow through a circuit?


  There must be 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 very strong electric field between them?


  Electrons in the air molecules will be strongly attracted towards the positively charged object, potentially causing a spark.
• How can electric fields be represented?


  Electric fields can be represented using a diagram with field lines.
• What do field lines in an electric field diagram show?


  Field lines show the direction of the force that a small positive charge would experience when placed in the electric field.
• What are the rules for drawing electric fields?


  • Field lines meet the surface of charged objects at 90°.
  • Arrows always point away from positive charges and towards negative charges.
• How can insulating materials become charged?

  Insulating materials can become charged when they are rubbed with another insulating material.
• What happens to materials that gain or lose electrons?


  Materials that gain electrons become negatively charged, and those that lose electrons become positively charged.
• How is electric charge measured?

  Electric charge is measured in coulombs (C).
• Why does an atom have no charge?

  An atom has no charge because it has equal numbers of positive protons and negative electrons.
• What happens when electrons are removed from or added to an atom?

  When electrons are removed from an atom, it becomes positively charged; when electrons are added, it becomes negatively charged.
• What are the definitions of the following key terms?

  • ampere
  • charge
  • coulomb
  • current
  • electric field
  • electrostatic force
  • LDR
  • parallel
  • potential difference
  • resistance
  • series
  • static
  • thermistor
  • Ampere: unit of current
  • Charge: property of matter that causes it to experience a force in an electric field
  • Coulomb: unit of electric charge
  • Current: rate of flow of charge
  • Electric field: region around a charged object where another charged object experiences a force
  • Electrostatic force: force between charged objects
  • LDR: light-dependent resistor
  • Parallel: circuit configuration with multiple paths for current
  • Potential difference: energy transferred per unit charge
  • Resistance: opposition to the flow of current
  • Series: circuit configuration where components are connected in a single loop
  • Static: stationary electric charge
  • Thermistor: temperature-dependent resistor
• What happens when a charged object is placed in the electric field of another charged object?

  It experiences electrostatic force, exerting a non-contact force on each other.
• What are the characteristics of electric fields and forces between charged objects?


  • Like charges repel each other.
  • Opposing charges attract each other.
  • The electric field strength increases as the distance decreases.
• What causes resistance in a circuit?


  Resistance is caused by electrons colliding with ions and atoms of the wires and components in the circuit.
• What is the unit of resistance?


  The unit of resistance is the ohm (Ω).
• Why does a long wire have more resistance than a short wire?


  A long wire has more resistance because electrons collide with more ions as they pass through it.
• How can the resistance of an electrical component be found?


  The resistance can be found by measuring the current and potential difference.
• What is the formula relating potential difference, current, and resistance?


  Potential difference (V) = current (A) × resistance (Ω).
• What is an I-V graph?


  An I-V graph is a graph of current through a component against the potential difference across it.
• What happens to the temperature of a filament as more current flows through it?


  The temperature increases, causing resistance to increase as well.
• How does the resistance of a thermistor change with temperature?


  The resistance of a thermistor decreases as temperature increases.
• How does the resistance of a light-dependent resistor (LDR) change with light intensity?


  The resistance of an LDR decreases as light intensity increases.
• What are the main features of a series circuit?


  • Same current through each component.
  • Total p.d. of power supply is shared between components.
  • Total resistance is the sum of the resistance of each component.
• What are the main features of a parallel circuit?


  • p.d. across each branch is the same.
  • Total current through circuit is the sum of the currents in each branch.
  • Total resistance is less than the smallest individual resistor.
• How does a material become charged?


  A material becomes negatively charged by gaining electrons and positively charged by losing electrons.
• What will two objects carrying the same type of charge do if they are brought close to each other?


  They will repel each other.
• What is an electric field?


  An electric field is a region of space around a charged object where another charged object will experience an electrostatic force.