E and Magnetic Fields

• What is a force field?

  An area with a non-contact force
• How can force fields be represented?

  As vectors and field line diagrams
• What does the distance between field lines indicate?


  The strength of the force exerted
• What is an electric field?

  A force field for charged particles
• What is electric field strength (E)?

  Force per unit charge in a field
• How is electric field strength calculated?

  $E =$$\frac{F}{Q}$
• When is electric field strength constant?

  In a uniform electric field
• What does Coulomb's law describe?

  The force between two point charges

  
• What is the formula for Coulomb's law?

  $F =$$\frac{Q_1 Q_2}{4 \pi \epsilon_0 r^2}$
• What happens if charges have the same sign?

  The force will be repulsive
• What happens if charges have different signs?

  The force will be attractive
• What forms a radial electric field?

  Point charges

  
• How is electric field strength calculated in a radial field?

  $E =$$\frac{Q}{4 \pi \epsilon_0 r^2}$
• What is absolute electric potential (V)?

  Potential energy per unit charge
• Where is the electric potential greatest?

  At the surface of a charge
• What happens to electric potential as distance increases?

  It decreases
• What determines the sign of electric potential?

  The sign of the charge (Q)
• What is the relationship between charge sign and potential?

  Positive charge has positive potential
• How can a uniform electric field be formed?

  Using parallel plates with potential difference

  
• How is electric field strength calculated between parallel plates?

  $E =$$\frac{V}{d}$
• What is the formula for electric potential in a radial field?

  $V =$$\frac{Q}{4 \pi \epsilon_0 r}$
• What is electric potential difference?

  Energy needed to move a unit charge
• How can electric fields be represented?

  By field lines and equipotential surfaces
• What do equipotential surfaces indicate?

  Same potential everywhere on the surface
• What happens when a charge moves along an equipotential surface?

  No work is done
• How are equipotential surfaces around a point charge shaped?

  They form concentric circles
• What is capacitance (C)?

  Charge stored per unit potential difference
• How is capacitance calculated?

  $C =$$\frac{Q}{V}$
• What is the formula for energy stored by a capacitor?

  $W =$$\frac{1}{2} QV$
• What does the area under a charge vs. potential difference graph represent?

  The electrical energy stored by a capacitor

  
• How can variations of the energy stored equation be derived?

  By substituting capacitance formulas into it
• What is the first variation of the energy stored equation?

  $W =$$\frac{1}{2} CV^2$
• What is the second variation of the energy stored equation?

  $W =$$\frac{1}{2} \frac{Q^2}{C}$
• How do you charge a capacitor?

  Connect it in a circuit with power supply
• What happens to current when charging a capacitor?

  Current decreases as charge builds up
• What is the time constant (RC)?

  Time taken to discharge to 0.37 value
• How can the time constant be calculated?

  From graphs of current, charge, and voltage
• What happens to current, charge, and potential during discharging?

  They all fall exponentially

  
• What is the relationship between time and values during charging and discharging?

  Same time to halve values
• What is the formula for charge in terms of current and time?

  $Q =$$I \times t$