Electrostatics Charges



  1. Which is bigger, a coulomb or charge on an electron? How many electronic charges from one coulomb of charge?
  2. Assume that each atom in a copper wire contributes one free electron. Estimate the number of free electrons in a copper wire having a mass of 6.4 g (take the atomic weight of copper to be 64 g/mol).
  3. How much positive & negative charge is there in a cup of water?
  4. If a body gives out  electrons every second, how much time is required to get a total charge of 1 C from it?
  5. Two charged particles having charge 2.0  C  each are joined by an insulating string of length 1 m & the system is kept on a smooth horizontal table. Find the tension in the string.
  6. The electrostatic force of repulsion between two positively charged ions carrying equal charge is 3.7 N, when they are separated by a distance of 5 Å. How many electrons are missing from each ion?
  7. A charge q is placed at the centre of the line joining two equal charges Q. Show that the system of three charges will be in equilibrium if q = – Q/4.
  8. Coulomb’s law for electrostatic force between two point charges & Newton’s law for gravitational force between two stationary point masses, both have inverse square dependence on the distance between the charges/masses (a) compare the strength of these forces by determining the ratio of their magnitudesfor an electron & a proton    (𝖎𝖎) for two protons (b) estimate the accelerations for electron & proton due to electrical force of their mutual attraction when they are 1 Å
  9. A charged metallic sphere A is suspended by a nylon thread. Another charged metallic sphere B carried by an insulating handle is brought close to A such that the distance between their centres is 10 cm as shown in Fig.
  10. Two equal positive charges, each of 2  interact with a third positive charge of 3  situated as shown in Fig. Calculate the magnitude & direction of the force on the

3  charge.












  1. Find the magnitude of the resultant force on a  2   C &  C at A & B respectively.

Given AP = 10 cm & BP = 5 cm.

APB = 90, Fig.










  1. Consider
  2. Consider the charges q
  3. Estimate
  4. Two fixed point