1 For coulomb force to be operative the least size of the atom will be a) 10ି଼ m b) 10ିଵହ m c) 10ିଵ଴ m d) 10ିଵଶ m 2 A conducting sphere of radius 10 cm is charged with 10 μC. Another uncharged sphere of radius 20 cm is allowed to touch it for some time. After that if the spheres are separated, then surface density of charges on the spheres will be in the ratio of a) 1: 1 b) 2: 1 c) 1: 3 d) 1: 2 3 When 10ଵଽ electrons are removed from a neutral metal plate, the electric charge on it is a) - 1.6 C b) 10ାଵଽ C c) +1.6 C d) 10ିଵଽ C 4 A charge q is placed at the center of the line joining two equal charges Q. The system of the three charges will be in equilibrium if q is equal to a) ொ ହ b) ொ ଶ c) ொ ସ d) ିொ ସ 5 A parallel plate air capacitor is charged to a potential difference of V volt. After disconnecting the charging battery, the distance between the plates of the capacitor is increased using an insulating handle. As a result, the potential difference between the plates. a) does not change b) increases c) becomes zero d) decreases 6 Which of the following is not the property of equipotential surfaces? a) They are concentric spheres for uniform electric fields. b) They can be imaginary spheres. c) They do not cross each other. d) Rate of change of potential with distance on them is zero.

1. A boy rubs his dog with a balloon. The dog gets 20,000 extra electrons.a. What is the charge on the dog?b. Then the boy rubs a piece of silk on his cat. The cat LOSES 30,000 electrons to the silk. What is thecharge on the CAT?c. Finally, the boy places his cat (20 kg) on frictionless ice and he places his dog (35 kg) standing 2maway on the edge of the ice.i. Calculate the electrostatic force on the CAT from the DOG. Do they ATTRACT or REPEL?ii. What is the initial acceleration of the cat?iii. What is the electrostatic force on the DOG from the CAT? Why is this answer the same as ordifferent from “i”?iv. What is the initial acceleration of the dog? Why is this answer the same as or different from “ii”?

a) Both A and R are true and R is the correct explanation of Ab) Both A and R are true but R is NOT the correct explanation of A c) A is true but R is falsed) A is false and R is also false1. Assertion (A): The electrostatics force increases with decrease the distance between thecharges.Reason (R): The electrostatic force of attraction or repulsion between any two stationarypoint charges is inversely proportional to the square of the distance between them.2. Assertion (A): The Coulomb force between two points charges depend upon the dielectricconstant of the intervening medium.Reason(R): Coulomb’s force varies inversely with the dielectric constant of medium.3. Assertion(A): The charge given to a metallic sphere does not depend on whether it is hollowor solidReason(R): The charge resides only at the surface of conductor.4. Assertion (A): A comb run through one’s dry hair attracts small bits of paper.Reason(R): Molecules in the paper gets polarized by the charged comb resulting in net force ofattraction5. Assertion (A): A proton is placed in a uniform electric field, it tend to move along thedirection of electric field.Reason(R): A proton is placed in a uniform electric field it experiences a force.6. Assertion (A): Electric field at the surface of a charged conductor is always normal to thesurface at every point.Reason(R): Electric field gives the magnitude & direction of electric force ( ) experienced by anycharge placed at any point.

Two parallel, infinite, nonconducting plates are 4.53 cm apart and have charge distributions of +2.25 μC/m2+2.25 μC/m2 and –2.25 μC/m2–2.25 μC/m2 . (a) What is the magnitude of the force on an electron in the space between the plates? (You may enter your calculation using scientific notation.)  N (b) What is the magnitude of the force on an electron located outside the two plates near the surface of one of the two plates?  N

How many electrons must be removed from an electrically neutral silver dollar to give it a charge of +3.8 C? 2. How many electrons would be required to have a total charge of 1.00 C? 3. Two point charges are separated by 10.0 cm. If one charge is +20.0 C and the other is –6.00 C, what is the force between them? 4. Determine the electrostatic force of attraction between a proton and a electron that are separated by a distance of 5.0 x 102 nm. 5. Two identical point charges are 3.00 cm apart. Find the charge on each of them if the force of repulsion is 4.00 x 10–7 N. 6. Two identical point charges are separated by a distance of 3.0 cm and they repel each other with a force of 4.0 x 10–5 N. What is the new force if the distance between the point charges is doubled? 7. An electric force of 2.5 x 10–4 N acts between two small, equally charged spheres which are 2.0 cm apart. Calculate the force acting between the spheres if the charge on one sphere is doubled and the spheres move to a 5.0 cm separation. 8. Three particles are placed on a straight line. The left particle has a charge of +4.6 x 10-6 C, the middle particle has a charge of –2.3 x 10-6 C, and the right particle has a charge of –2.3 x 10-6 C. The particle on the left is 12 cm from the middle particle and the right particle is 24 cm from the middle particle. Find the total force on the middle particle. 9. Three charges are located on a straight line. A charge of +7.5 C is 0.4 cm from a –4.0 C charge. The –4.0 C charge is in turn 0.6 cm away from a +9.0 C charge. What is the net electric force on the middle (-4.0 C) charge? 10. Three charges are located in an equilateral triangle with sides of 0.5 m. The charge located at the top is +3.5C while the two bottom charges are +5.0 C and –5.0 C. What is the net electric force (magnitude and direction) acting on the top charge?

2. Small area in the center of an atom in which most of the atom’s mass and positive charge is concentrated is called the ____________.