Lecture 7

• What are the integral parts of modern life?

  Electric power and electronics
• What does electromagnetics study?

  Theory and applications of electric and magnetic fields
• What concept arose from the action at a distance of forces?

  The concept of fields in a region
• What is electrostatics?

  The physics of stationary charges

  
• What are the two kinds of charge?

  Positive charge and negative charge
• What does it mean for an object to be charged?

  It has an excess charge, positive or negative
• What does the conservation of charge state?

  Charge can neither be created nor destroyed
• What is the unit of charge?

  Coulomb [C]

  
• What are some devices based on electrostatics?

  X-ray machines, oscilloscopes, and ECG
• What happens when two glass rods are rubbed with silk cloth?

  They repel each other due to same charge

  
• What occurs when a plastic rod is rubbed with fur?

  It attracts a glass rod due to opposite charges
• What happens to an atom when electrons are removed?

  It becomes positively charged (positive ion)
• What is Coulomb's Law used for?

  To calculate the electrostatic force between charges
• What is the formula for Coulomb's Law?

  F = k * (q1 * q2) / r^2
• What is the value of the Coulomb constant k?

  k ≈ 9 × 10^9 [N·m²/C²]

  
• What does the Coulomb constant k represent?

  The force between two 1 C charges at 1 m

  
• What does the superposition principle state in electrostatics?

  The net force is the vector sum of individual forces
• What is the charge of an electron?

  e = 1.602 × 10^-19 C
• What is an electric field?

  Regions around a charge where electric force exists
• What characterizes an electric field?

  Field intensity, electric flux, and potential
• How is electric field intensity defined?

  As electric force per unit charge

  
• What direction do electric field lines point for positive charges?

  Outwards from the charge

  
• What direction do electric field lines point for negative charges?

  Inwards towards the charge
• What does electric flux represent?

  The amount of electric field lines piercing a surface
• What is electric flux density defined as?

  Amount of electric flux crossing a unit surface
• What is the formula for electric flux density?

  D = εE

  
• What is electric potential associated with?

  Work done per unit charge against electric force
• What is the unit of electric potential?

  Volts [V]
• What does the superposition principle in electric fields state?

  The net electric field is the vector sum of individual fields

  
• What does Gauss's Law allow us to find?

  The source of electric field (charge) when known
• What does the electric field mapping show for a uniform electric field?

  Lines of E are parallel and equipotential lines are orthogonal

  
• What is a conductor?

  A material that carries electric current
• How do metallic conductors carry charge?

  By free electrons
• What is electrical conductivity measured in?

  Siemens per metre (S/m)
• What happens in a perfect conductor?

  There is no electric field inside the conductor
• What is the energy stored in a capacitor formula?

  W = (1/2)CV²
• What does the work done in charging a capacitor represent?

  Stored as potential energy in the capacitor
• What are the key parameters characterizing an electric field?

  • Field intensity (E)
  • Electric flux (ψ)
  • Flux density (D)
  • Potential (V)
  • Potential difference (ΔV)
  • Field energy (W)
• What are the types of materials based on electrical properties?

  • Conductors: carry electric current (e.g., metals)
  • Insulators: do not carry electric current (e.g., glass)
  • Semiconductors: intermediate conductivity (e.g., silicon)
• What is the relationship between electric field intensity and electric potential?

  • Electric field intensity (E) is the gradient of electric potential (V).
  • E = -dV/dx