electric fields

• What creates electric fields?

  Presence of electric charge
• How can a charged sphere be modeled?

  As a point charge at its center
• What direction do electric field lines always go?

  From positive to negative
• At what angle do electric field lines enter and leave surfaces?

  At 90 degrees
• How would you draw field lines for a positive charge?

  Radially outward from the charge
• How would you draw field lines for a negative charge?

  Radially inward towards the charge
• What happens to the electric field between two unlike charges?

  There is a net electric field between them
• What happens to the electric field between two like charges?

  No net electric field exists between them
• How do electric field lines behave near a charged plate?

  They go from positive to negative at 90 degrees
• What is electric field strength defined as?

  Force per unit charge
• What is the formula for electric field strength?

  Force divided by charge
• What is the unit for electric field strength?

  Newtons per coulomb
• What is the base unit for electric field strength derived from?

  Force and charge units
• How do you derive the base unit for electric field strength?

  By dividing kg m/s² by A s
• What is Coulomb's law used for?

  Calculating the force between two charges
• What does Coulomb's law state about two charges?

  They experience a force based on their charges
• What is the formula for the force between two charges?

  $F =$$\frac{qq}{4 \pi \epsilon_0 r^2}$
• What is the approximate value of $\epsilon_0$?


  $8.8 \times 10^{-12}$
• What is a common error in calculating force using Coulomb's law?

  Forgetting to square the distance
• How is electric field strength related to force?

  Electric field strength equals force divided by charge
• What is the expression for electric field strength around a point charge?

  $E =$$\frac{q}{4 \pi \epsilon_0 r^2}$
• How can you find electric field strength at different distances?

  Substitute the distance into the equation
• What is the mass of a proton?

  $1.67 \times 10^{-27} \text{ kg}$
• What forces do two protons experience?

  Repulsive electric and attractive gravitational forces
• What is the gravitational constant?

  $6.67 \times 10^{-11}$
• How do you calculate gravitational force between two protons?

  Using Newton's law of universal gravitation
• What is the formula for gravitational force?

  $F_g =$$\frac{-G m^2}{r^2}$
• What is the approximate value of the electrostatic force between two protons?

  $1.24 \times 10^{36}$
• How do electric fields compare to gravitational fields?

  Electric fields can be attractive or repulsive
• What is the formula for electric field strength?

  $E =$$\frac{F}{q}$
• What is the formula for gravitational field strength?

  $g =$$\frac{F}{m}$
• How are the field strengths for electric and gravitational fields expressed?

  Both are force per unit charge or mass
• What is the electric field between two parallel plates?

  Uniformly directed from positive to negative
• What is the formula for electric field strength between parallel plates?

  $E =$$\frac{V}{d}$
• What does the formula for electric field strength between parallel plates apply to?

  Only for uniform electric fields
• What is the capacitance of a parallel plate capacitor without an insulator?

  $C =$$\frac{\epsilon_0 A}{d}$
• How does inserting a dielectric affect capacitance?

  It increases capacitance by a factor
• What is the relative permittivity?

  Factor by which capacitance increases
• What is the formula for the electric field between two parallel plates?

  Electric field = V / d
• When does the formula for electric field apply?

  When the field is uniform between plates