# Electrostatics Charges

PAPER – PHYSICS

- Which is bigger, a coulomb or charge on an electron? How many electronic charges from one coulomb of charge?
- 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).
- How much positive & negative charge is there in a cup of water?
- If a body gives out electrons every second, how much time is required to get a total charge of 1 C from it?
- 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.
- 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?
- 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.
- 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
- 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.
- 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.

A

B

o

- 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.

- Consider
- Consider the charges q
- Estimate
- Two fixed point