Electric & 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 is an electric field?

  A force field for charged particles
• What does the distance between field lines represent?

  The strength of the force exerted
• 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 when charges have the same sign?

  The force is repulsive
• What happens when charges have different signs?

  The force is 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 electric potential greatest?

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

  It decreases
• What is the electric potential at infinity?

  Zero
• How does the sign of charge affect electric potential?

  Positive charge has positive potential
• What is the effect of a negative charge on electric potential?

  It makes potential negative
• How is a uniform electric field 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 field lines indicate in an electric field?

  The direction of force on a positive charge

  
• What characterizes a uniform electric field?

  Same electric force everywhere in the field
• What happens to the magnitude of force in a radial field?

  It decreases with distance from the charge
• What are equipotential surfaces?

  Surfaces with the same potential everywhere
• What happens when a charge moves along an equipotential surface?

  No work is done
• What is capacitance (C)?

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

  $C =$$\frac{Q}{V}$
• How is electrical energy stored by a capacitor (W) represented?

  Area under charge vs. potential graph

  
• What is the formula for energy stored by a capacitor?

  $W =$$\frac{1}{2} QV$
• How can you derive variations of the energy stored equation?

  By substituting capacitance into the energy formula
• 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{C}{Q^2}$
• How do you charge a capacitor?

  Connect it in a circuit with power supply
• What happens when a capacitor is connected to a power supply?

  Current flows and charge builds up
• What happens to current as charge increases in a capacitor?

  Current decreases due to electrostatic repulsion
• How is a capacitor discharged?

  Connect it to a closed circuit with a resistor