Content text 17. Electrostatics Easy.pdf
1. The law, governing the force between electric charges is known as (a) Ampere's law (b) Ohm's law (c) Faraday's law (d) Coulomb's law 2. When the distance between the charged particles is halved, the force between them becomes (a) One-fourth (b) Half (c) Double (d) Four times 3. There are two charges +1 microcoulombs and +5 microcoulombs. The ratio of the forces acting on them will be (a) 1 : 5 (b) 1 : 1 (c) 5 : 1 (d) 1 : 25 4. A charge 1 q exerts some force on a second charge q2 . If third charge q3 is brought near, the force of 1 q exerted on q2 (a) Decreases (b) Increases (c) Remains unchanged (d) Increases if q3 is of the same sign as 1 q and decreases if q3 is of opposite sign 5. Fg and Fe represents gravitational and electrostatic force respectively between electrons situated at a distance 10 cm. The ratio of Fg Fe / is of the order of (a) 42 10 (b) 10 (c) 1 (d) 43 10 − 6. The ratio of the forces between two small spheres with constant charge (a) in air (b) in a medium of dielectric constant K is (a) 1 : K (b) K : 1 (c) 2 1 : K (d) : 1 2 K 7. A soap bubble is given a negative charge, then its radius (a) Decreases (b) Increases (c) Remains unchanged (d) Nothing can be predicted as information is insufficient 8. Four charges are arranged at the corners of a square ABCD , as shown in the adjoining figure. The force on the charge kept at the centre O is (a) Zero (b) Along the diagonal AC (c) Along the diagonal BD (d) Perpendicular to side AB 9. In the absence of other conductors, the surface charge density (a) Is proportional to the charge on the conductor and its surface area (b) Inversely proportional to the charge and directly proportional to the surface area (c) Directly proportional to the charge and inversely proportional to the surface area (d) Inversely proportional to the charge and the surface area 10. A body can be negatively charged by (a) Giving excess of electrons to it (b) Removing some electrons from it (c) Giving some protons to it (d) Removing some neutrons from it 11. The minimum charge on an object is (a) 1 coulomb (b) 1 stat coulomb (c) 19 1.6 10 − coulomb (d) 19 3.2 10 − coulomb 12. Out of gravitational, electromagnetic, Vander Waals, electrostatic and nuclear forces; which two are able to provide an attractive force between two neutrons (a) Electrostatic and gravitational (b) Electrostatic and nuclear (c) Gravitational and nuclear (d) Some other forces like Vander Waals 13. A total charge Q is broken in two parts Q1 and Q2 and they are placed at a distance R from each other. The maximum force of repulsion between them will occur, when (a) R Q Q Q R Q Q2 = , 1 = − (b) 3 2 , 4 2 1 Q Q Q Q Q = = − (c) 4 3 , 4 2 1 Q Q Q Q = = (d) 2 , 2 1 2 Q Q Q Q = = 14. Three charges 4q,Q and q are in a straight line in the position of 0, l / 2 and l respectively. The resultant force on q will be zero, if Q = (a) – q (b) − 2q (c) 2 q − (d) 4 q 15. An isolated solid metallic sphere is given +Q charge. The charge will be distributed on the sphere (a) Uniformly but only on surface O C +q +2q A B +q D – 2q
(b) Only on surface but non-uniformly (c) Uniformly inside the volume (d) Non-uniformly inside the volume 16. Two small spheres each having the charge +Q are suspended by insulating threads of length L from a hook. This arrangement is taken in space where there is no gravitational effect, then the angle between the two suspensions and the tension in each will be (a) 2 2 4 0 (2 ) 1 180 , L o Q (b) 2 2 4 0 1 90 , L o Q (c) 2 2 4 0 2 1 180 , L o Q (d) 2 2 4 0 1 180 , L o Q 17. Two charges each of 1 coulomb are at a distance 1km apart, the force between them is (a) Newton 3 9 10 (b) Newton 3 9 10 − (c) Newton 4 1.1 10 − (d) Newton 4 10 18. +2C and +6C two charges are repelling each other with a force of 12 N . If each charge is given −2C of charge, then the value of the force will be (a) 4N (Attractive) (b) 4N (Repulsive) (c) 8N (Repulsive) (d) Zero 19. Dielectric constant of pure water is 81. Its permittivity will be (a) MKS 10 7.12 10 − units (b) MKS 12 8.86 10 − units (c) MKS 13 1.02 10 units (d) Cannot be calculated 20. There are two metallic spheres of same radii but one is solid and the other is hollow, then (a) Solid sphere can be given more charge (b) Hollow sphere can be given more charge (c) They can be charged equally (maximum) (d) None of the above 21. In general, metallic ropes are suspended on the carriers which take inflammable material. The reason is (a) There speed is controlled (b) To keep the centre of gravity of the carrier nearer to the earth (c) To keep the body of the carrier in contact with the earth (d) Nothing should be placed under the carrier 22. Three equal charges are placed on the three corners of a square. If the force between 1 q and q2 is F12 and that between 1 q and q3 is F13 , the ratio of magnitudes 13 12 F F is (a) 1 / 2 (b) 2 (c) 1 / 2 (d) 2 23. ABC is a right angled triangle in which AB = 3 cm and BC = 4 cm . And ABC = /2. The three charges +15, + 12 and −20 e.s.u. are placed respectively on A , B and C . The force acting on B is (a) 125 dynes (b) 35 dynes (c) 25 dynes (d) Zero 24. With the rise in temperature, the dielectric constant K of a liquid (a) Increases (b) Decreases (c) Remains unchanged (d) Charges erratically 25. Two charges 1 q and q2 are placed in vacuum at a distance d and the force acting between them is F . If a medium of dielectric constant 4 is introduced around them, the force now will be (a) 4F (b) 2F (c) 2 F (d) 4 F 26. Force of attraction between two point charges Q and – Q separated by d metre is Fe . When these charges are placed on two identical spheres of radius R = 0.3 d whose centres are d metre apart, the force of attraction between them is (a) Greater than Fe (b) Equal to Fe (c) Less than Fe (d) Less than Fe 27. When 14 10 electrons are removed from a neutral metal sphere, the charge on the sphere becomes (a) 16 C (b) −16 C (c) 32 C (d) −32 C 28. A force F acts between sodium and chlorine ions of salt (sodium chloride) when put 1cm apart in air. The permittivity of air and dielectric constant of water are 0 and K respectively. When a piece of salt is put in water electrical force acting between sodium and chlorine ions 1cm apart is (a) K F (b) 0 FK (c) 0 K F (d) K F 0 29. A conductor has coulombs 19 14.4 10 − positive charge. The conductor has(Charge on electron coulombs 19 1.6 10 − = ) (a) 9 electrons in excess (b) 27 electrons in short (c) 27 electrons in excess (d) 9 electrons in short
30. The value of electric permittivity of free space is (a) 9 2 2 9 10 NC / m (b) Nm C sec 12 2 2 8.85 10 / − (c) 12 2 2 8.85 10 C / Nm − (d) 9 2 2 9 10 C / Nm 31. Two similar spheres having + q and −q charge are kept at a certain distance. F force acts between the two. If in the middle of two spheres, another similar sphere having + q charge is kept, then it experience a force in magnitude and direction as (a) Zero having no direction (b) 8F towards + q charge (c) 8F towards −q charge (d) 4F towards + q charge 32. A charge Q is divided into two parts of q and Q − q . If the coulomb repulsion between them when they are separated is to be maximum, the ratio of q Q should be (a) 2 (b) 1 / 2 (c) 4 (d) 1 / 4 33. Number of electrons in one coulomb of charge will be (a) 29 5.46 10 (b) 18 6.25 10 (c) 19 1.6 10 + (d) 11 9 10 34. When air is replaced by a dielectric medium of constant k , the maximum force of attraction between two charges separated by a distance (a) Decreases k times (b) Remains unchanged (c) Increases k times (d) Increases −1 k times 35. A glass rod rubbed with silk is used to charge a gold leaf electroscope and the leaves are observed to diverge. The electroscope thus charged is exposed to X-rays for a short period. Then (a) The divergence of leaves will not be affected (b) The leaves will diverge further (c) The leaves will collapse (d) The leaves will melt 36. One metallic sphere A is given positive charge whereas another identical metallic sphere B of exactly same mass as of A is given equal amount of negative charge. Then (a) Mass of A and mass of B still remain equal (b) Mass of A increases (c) Mass of B decreases (d) Mass of B increases 37. The force between two charges 0.06 m apart is 5 N . If each charge is moved towards the other by 0.01 m , then the force between them will become (a) 7.20 N (b) 11.25 N (c) 22.50 N (d) 45.00 N 38. Two charged spheres separated at a distance d exert a force F on each other. If they are immersed in a liquid of dielectric constant 2, then what is the force (if all conditions are same) (a) 2 F (b) F (c) 2F (d) 4F 39. Two point charges +3C and +8C repel each other with a force of 40N . If a charge of −5C is added to each of them, then the force between them will become (a) −10N (b) +10N (c) +20N (d) −20N 40. When 19 10 electrons are removed from a neutral metal plate, the electric charge on it is (a) – 1.6 C (b) + 1.6 C (c) 10+19 C (d) 10–19 C 41. Electric charges of 1C,−1C and 2C are placed in air at the corners A, B and C respectively of an equilateral triangle ABC having length of each side 10 cm. The resultant force on the charge at C is (a) 0.9 N (b) 1.8 N (c) 2.7 N (d) 3.6 N 42. Charge on -particle is (a) C 19 4.8 10 − (b) C 19 1.6 10 − (c) C 19 3.2 10 − (d) C 19 6.4 10 − 43. Two small conducting spheres of equal radius have charges +10 C and −20 C respectively and placed at a distance R from each other experience force F1 . If they are brought in contact and separated to the same distance, they experience force F2 . The ratio of F1 to F2 is (a) 1 : 8 (b) – 8 : 1 (c) 1 : 2 (d) – 2 : 1 44. Two charges each equal to 2C are 0.5m apart. If both of them exist inside vacuum, then the force between them is (a) 1.89 N (b) 2.44 N (c) 0.144 N (d) 3.144 N 45. Two charges are at a distance ‘d’ apart. If a copper plate (conducting medium) of thickness 2 d is placed between them, the effective force will be (a) 2F (b) F / 2 (c) 0 (d) 2F
46. Two electrons are separated by a distance of 1Å. What is the coulomb force between them (a) 8 2.3 10 − N (b) 8 4.6 10 − N (c) 8 1.5 10 − N (d) None of these 47. Two copper balls, each weighing 10g are kept in air 10 cm apart. If one electron from every 6 10 atoms is transferred from one ball to the other, the coulomb force between them is (atomic weight of copper is 63.5) (a) 10 2.0 10 N (b) 4 2.0 10 N (c) 8 2.0 10 N (d) 6 2.0 10 N 48. A solid conducting sphere of radius a has a net positive charge 2Q. A conducting spherical shell of inner radius b and outer radius c is concentric with the solid sphere and has a net charge – Q. The surface charge density on the inner and outer surfaces of the spherical shell will be (a) 2 2 4 , 4 2 c Q b Q − (b) 2 2 4 , 4 c Q b Q − (c) 2 4 0, c Q (d) None of the above 49. Three charges each of magnitude q are placed at the corners of an equilateral triangle, the electrostatic force on the charge placed at the center is (each side of triangle is L) (a) Zero (b) 2 2 4 0 1 L q (c) 2 2 0 3 4 1 L q (d) 2 2 12 0 1 L q 50. Two charges placed in air repel each other by a force of N 4 10 − . When oil is introduced between the charges, the force becomes N 5 2.5 10 − . The dielectric constant of oil is (a) 2.5 (b) 0.25 (c) 2.0 (d) 4.0 51. Three charges are placed at the vertices of an equilateral triangle of side ‘a’ as shown in the following figure. The force experienced by the charge placed at the vertex A in a direction normal to BC is (a) /(4 ) 2 0 2 Q a (b) /(4 ) 2 Q 0a − (c) Zero (d) /(2 ) 2 0 2 Q a 52. Two particle of equal mass m and charge q are placed at a distance of 16 cm. They do not experience any force. The value of m q is (a) l (b) G 0 (c) 4 0 G (d) 4 0G 53. When a glass rod is rubbed with silk, it (a) Gains electrons from silk (b)Gives electrons to silk (c) Gains protons from silk (d) Gives protons to silk 54. An electron is moving round the nucleus of a hydrogen atom in a circular orbit of radius r. The coulomb force F between the two is (Where 4 0 1 K = ) (a) r r e K ˆ 3 2 − (b) r r e K 3 2 (c) r r e K 3 2 − (d) r r e K ˆ 2 2 55. A body has – 80 micro coulomb of charge. Number of additional electrons in it will be (a) 5 8 10 − (b) 17 80 10 − (c) 14 5 10 (d) 17 1.28 10 − 56. Two point charges placed at a certain distance r in air exert a force F on each other. Then the distance r' at which these charges will exert the same force in a medium of dielectric constant k is given by (a) r (b) r/k (c) r / k (d) r k 57. Dielectric constant for metal is (a) Zero (b) Infinite (c) 1 (d) Greater than 1 58. A charge of Q coulomb is placed on a solid piece of metal of irregular shape. The charge will distribute itself (a) Uniformly in the metal object (b) Uniformly on the surface of the object (c) Such that the potential energy of the system is minimised (d) Such that the total heat loss is minimised 59. Five balls numbered 1 to 5 are suspended using separate threads. Pairs (1, 2), (2, 4) and (4, 1) show electrostatic attraction, while pair (2, 3) and (4, 5) show repulsion. Therefore ball 1 must be (a) Positively charged (b) Negatively charged (c) Neutral (d) Made of metal c b a A +Q B a C – Q + Q
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