practice

  1. Compare the electrostatic and gravitational forces between …
    1. an electron and proton in a hydrogen atom (the radius of the electron's orbit is about 53 pm)
    2. two protons in a helium nucleus with two neutrons between them (the radius of a neutron is about 1.2 fm)
  2. If the moon were held in its orbit by an electrostatic rather than gravitational force …
    1. What quantity of charge would be needed?
    2. How many elementary charges is this?
    If all of the charge came from the separation of hydrogen atoms into electrons and protons …
    1. What mass of hydrogen would be required?
    2. How many liters of H2 gas at STP would be required?
  3. Given three charges in a standard coordinate system, calculate the magnitude and direction of the net electrostatic force on each.
    1. +10 μC at (0 m, 0 m)
    2. −20 μC at (0 m, +3 m)
    3. +25 μC at (−4 m, 0 m)
  4. Write something completely different.

conceptual

  1. How does the electrostatic force exerted by a proton on an electron compare to the electrostatic force exerted by an electron on a proton? How does the gravitational force exerted by a proton on an electron compare to the gravitational force exerted by an electron on a proton?
  2. If electric forces are so much more powerful than gravitational forces, why do we notice the gravitational field of the Earth but not its electric field?