Work Done on a Charge

• What is the formula for work done on a charge?

  ∆W = q∆V
• What does ∆W represent in the formula ∆W = q∆V?

  Work done (J)
• What does q represent in the equation ∆W = q∆V?

  Magnitude of charge moving in the field (C)
• How does electric potential change with distance from a charge?

  Increases with distance from negative charge

  
• What is the formula for electric potential difference between two points?

  ∆V = Vf − Vi
• What does Vf represent in the equation ∆V = Vf − Vi?

  Final electric potential (J C)
• What does Vi represent in the equation ∆V = Vf − Vi?

  Initial electric potential (J C)
• How is potential difference due to a point charge expressed?

  ∆V = $\frac{Q}{4\pi\epsilon_0}\left(\frac{1}{r_f} - \frac{1}{r_i}\right)$
• What does Q represent in the potential difference formula?

  Magnitude of point charge producing the potential
• What does ε represent in the potential difference formula?

  Permittivity of free space (F m)
• What does r represent in the potential difference formula?

  Distance from charge Q (m)
• What is the formula for electric potential energy of two point charges?

  Ep = $\frac{Q_1Q_2}{4\pi\epsilon_0r}$
• What does the work done on a point charge equal?

  Change in electric potential energy
• What happens to electric potential energy when V = 0?

  Then Ep = 0
• How is the change in electric potential energy expressed?

  ∆Ep = q∆V = $\frac{Qq}{4\pi\epsilon_0}\left(\frac{1}{r_2} - \frac{1}{r_1}\right)$
• What does r1 represent in the change in electric potential energy formula?

  Initial distance of q from charge Q (m)
• What does r2 represent in the change in electric potential energy formula?

  Final distance of q from charge Q (m)
• When is work done on a point charge?

  When moving it away from another charge
• What happens when a positive charge moves against electric field lines?

  Work is done

  
• What happens when a negative charge moves with electric field lines?

  Work is done
• How do you calculate the work done when a charge moves from R to S?

  Use W = q∆V
• How do you calculate the electric potential difference between R and S?

  Use ∆V = $\frac{Q}{4\pi\epsilon_0}\left(\frac{1}{r_S} - \frac{1}{r_R}\right)$
• What is the calculated electric potential difference between R and S?

  ∆V = 133.5 V
• How do you calculate the work done by the moving charge?

  Use W = q∆V
• What are equipotential lines and surfaces?

  • Join points with the same electric potential
  • Perpendicular to electric field lines
  • Represented by dotted lines
  • Equal distance from the source charge

  
• How do equipotential lines behave in a radial field?

  • Concentric circles around the charge
  • Become progressively further apart with distance

  
• What is the characteristic of equipotential surfaces for multiple charges?

  • Curves drawn perpendicular to field lines
  • Central line at 0 V for opposite charges
  • Region of empty space for like charges

  
• How do equipotential lines behave in a uniform field?

  • Horizontal straight lines
  • Parallel and equally spaced
  • Perpendicular to field lines

  
• What can be assumed about two charges if their field lines point outwards?

  Both charges are positive

  
• What indicates a larger charge in terms of field lines?

  Greater density of field lines
• What does the point of zero electric field strength indicate?

  Closer to the right charge
• What is the distinction between radial and uniform fields?

  • Radial field: lines follow radius of a circle
  • Uniform field: lines are uniform distance apart
• Why do equipotential lines not have arrows?

  They are not vectors and have no direction