Tiêu đề 18. Current Electricity Easy 1.pdf ✅

1. Current of 4.8 amperes is flowing through a conductor. The number of electrons per second will be (a) 19 3 10 (b) 21 7.68 10 (c) 20 7.68 10 (d) 20 3 10 2. When the current i is flowing through a conductor, the drift velocity is v . If 2i current is flowed through the same metal but having double the area of cross-section, then the drift velocity will be (a) v / 4 (b) v / 2 (c) v (d) 4v 3. When current flows through a conductor, then the order of drift velocity of electrons will be (a) 10 / sec 10 m (b) 10 / sec 2 cm − (c) 10 / sec 4 cm (d) 10 / sec 1 cm − 4. Every atom makes one free electron in copper. If 1.1 ampere current is flowing in the wire of copper having 1 mm diameter, then the drift velocity (approx.) will be (Density of copper 3 3 9 10 − =  kgm and atomic weight = 63) (a) 0.3 mm / sec (b) 0.1mm / sec (c) 0.2 mm / sec (d) 0.2 cm / sec 5. Which one is not the correct statement (a) 1volt1 coulomb = 1 joule (b) 1volt1 ampere = 1 joule / second (c) 1volt1watt = 1 H.P. (d) Watt-hour can be expressed in eV 6. If a 0.1 % increase in length due to stretching, the percentage increase in its resistance will be (a) 0.2 % (b) 2 % (c) 1 % (d) 0.1 % 7. The specific resistance of manganin is  ohm m −8 50 10 . The resistance of a cube of length 50 cm will be (a) ohm 6 10 − (b) ohm 5 2.5 10 −  (c) ohm 8 10 − (d) ohm 4 5 10 −  8. The resistivity of iron is  ohm −m −7 1 10 . The resistance of a iron wire of particular length and thickness is 1 ohm. If the length and the diameter of wire both are doubled, then the resistivity in ohm −m will be (a) 7 1 10 −  (b) 7 2 10 −  (c) 7 4 10 −  (d) 7 8 10 −  9. The temperature coefficient of resistance for a wire is 0.00125 / C . At 300K its resistance is 1 ohm. The temperature at which the resistance becomes 2 ohm is (a) 1154 K (b) 1100 K (c) 1400 K (d) 1127 K 10. When the length and area of cross-section both are doubled, then its resistance (a) Will become half (b) Will be doubled (c) Will remain the same (d) Will become four times 11. The resistance of a wire is 20 ohms. It is so stretched that the length becomes three times, then the new resistance of the wire will be (a) 6.67 ohms (b) 60.0 ohms (c) 120 ohms (d) 180.0 ohms 12. The resistivity of a wire (a) Increases with the length of the wire (b) Decreases with the area of cross-section (c) Decreases with the length and increases with the cross- section of wire (d) None of the above statement is correct 13. Ohm's law is true (a) For metallic conductors at low temperature (b) For metallic conductors at high temperature (c) For electrolytes when current passes through them (d) For diode when current flows 14. The example for non-ohmic resistance is (a) Copper wire (b) Carbon resistance (c) Diode (d) Tungston wire 15. Drift velocity d v varies with the intensity of electric field as per the relation (a) vd  E (b) E vd 1  (c) = constant d v (d) 2 vd  E 16. On increasing the temperature of a conductor, its resistance increases because (a) Relaxation time decreases (b) Mass of the electrons increases (c) Electron density decreases (d) None of the above 17. In a conductor 4 coulombs of charge flows for 2 seconds. The value of electric current will be (a) 4 volts (b) 4 amperes (c) 2 amperes (d) 2 volts 5. The specific resistance of a wire is  , its volume is 3 3 m and its resistance is 3 ohms, then its length will be
(a)  1 (b)  3 (c) 3 1  (d) 3 1  19. 18 62.5 10 electrons per second are flowing through a wire of area of cross-section 0.1 2 m , the value of current flowing will be (a) 1 A (b) 0.1 A (c) 10 A (d) 0.11 A 20. A piece of wire of resistance 4 ohms is bent through 180  at its mid point and the two halves are twisted together, then the resistance is (a) 8 ohms (b) 1 ohm (c) 2 ohms (d) 5 ohms 21. When a piece of aluminium wire of finite length is drawn through a series of dies to reduce its diameter to half its original value, its resistance will become (a) Two times (b) Four times (c) Eight times (d) Sixteen times 22. A wire 100 cm long and 2.0 mm diameter has a resistance of 0.7 ohm, the electrical resistivity of the material is (a)  ohm  m −6 4.4 10 (b)  ohm  m −6 2.2 10 (c)  ohm  m −6 1.1 10 (d)  ohm  m −6 0.22 10 23. A certain wire has a resistance R . The resistance of another wire identical with the first except having twice its diameter is (a) 2 R (b) 0.25 R (c) 4 R (d) 0.5 R 24. In hydrogen atom, the electron makes 15 6.6 10 revolutions per second around the nucleus in an orbit of radius m 10 0.5 10 −  . It is equivalent to a current nearly (a) 1 A (b) 1 mA (c) 1A (d) A 19 1.6 10 −  25. A wire of length 5 m and radius 1 mm has a resistance of 1 ohm. What length of the wire of the same material at the same temperature and of radius 2 mm will also have a resistance of 1 ohm (a) 1.25 m (b) 2.5 m (c) 10 m (d) 20 m 26. When there is an electric current through a conducting wire along its length, then an electric field must exist (a) Outside the wire but normal to it (b) Outside the wire but parallel to it (c) Inside the wire but parallel to it (d) Inside the wire but normal to it 27. Through a semiconductor, an electric current is due to drift of (a) Free electrons (b) Free electrons and holes (c) Positive and negative ions (d) Protons 28. In an electrolyte 18 3.2 10 bivalent positive ions drift to the right per second while 18 3.6 10 monovalent negative ions drift to the left per second. Then the current is (a) 1.6 amp to the left (b) 1.6 amp to the right (c) 0.45 amp to the right (d) 0.45 amp to the left 29. A metallic block has no potential difference applied across it, then the mean velocity of free electrons is T = absolute temperature of the block) (a) Proportional to T (b) Proportional to T (c) Zero (d) Finite but independent of temperature 30. The specific resistance of all metals is most affected by (a) Temperature (b) Pressure (c) Degree of illumination (d) Applied magnetic field 31. The positive temperature coefficient of resistance is for (a) Carbon (b) Germanium (c) Copper (d) An electrolyte 32. The fact that the conductance of some metals rises to infinity at some temperature below a few Kelvin is called (a) Thermal conductivity (b) Optical conductivity (c) Magnetic conductivity (d) Superconductivity 33. Dimensions of a block are 1cm 1cm 100 cm . If specific resistance of its material is  ohm − m −7 3 10 , then the resistance between the opposite rectangular faces is (a) ohm 9 3 10 −  (b) ohm 7 3 10 −  (c) ohm 5 3 10 −  (d) ohm 3 3 10 −  34. There is a current of 20 amperes in a copper wire of 6 10 − square metre area of cross-section. If the number of free electrons per cubic metre is 29 10 , then the drift velocity is (a) 125 10 m / sec −3  (b) 12.5 10 m / sec −3  (c) 1.25 10 m / sec −3  (d) 1.25 10 m / sec −4  35. The electric intensity E , current density j and specific resistance k are related to each other by the relation (a) E = j / k (b) E = jk (c) E = k / j (d) k = jE
36. The resistance of a wire of uniform diameter d and length L is R . The resistance of another wire of the same material but diameter 2d and length 4L will be (a) 2R (b) R (c) R / 2 (d) R / 4 37. There is a current of 1.344 amp in a copper wire whose area of cross-section normal to the length of the wire is 1 2 mm . If the number of free electrons per 3 cm is 22 8.4  10 , then the drift velocity would be (a) 1.0 mm / sec (b) 1.0 m / sec (c) 0.1 mm / sec (d) 0.01 mm / sec 38. It is easier to start a car engine on a hot day than on a cold day. This is because the internal resistance of the car battery (a) Decreases with rise in temperature (b) Increases with rise in temperature (c) Decreases with a fall in temperature (d) Does not change with a change in temperature 39. 5 amperes of current is passed through a metallic conductor. The charge flowing in one minute in coulombs will be (a) 5 (b) 12 (c) 1/12 (d) 300 40. Two wires of the same material are given. The first wire is twice as long as the second and has twice the diameter of the second. The resistance of the first will be (a) Twice of the second (b) Half of the second (c) Equal to the second (d) Four times of the second 41. An electric wire is connected across a cell of e.m.f. E. The current I is measured by an ammeter of resistance R. According to ohm's law (a) E I R 2 = (b) E = IR (c) E = R / I (d) E = I / R 42. The resistances of a wire at temperatures tC and 0C are related by (a) (1 ) 0 R R t t = + (b) (1 ) 0 R R t t = − (c) (1 ) 2 0 R R t t = + (d) (1 ) 2 0 R R t t = − 43. An electric wire of length ‘I’ and area of cross-section a has a resistance R ohms. Another wire of the same material having same length and area of cross-section 4a has a resistance of (a) 4R (b) R/4 (c) R/16 (d) 16R 44. For which of the following the resistance decreases on increasing the temperature (a) Copper (b) Tungsten (c) Germanium (d) Aluminium 45. If n, e, and m respectively represent the density, charge relaxation time and mass of the electron, then the resistance of a wire of length l and area of cross-section A will be (a) ne A ml  2 (b) ne l m A 2 2  (c) ml ne A 2 2  (d) m l ne A 2  2 46. The relaxation time in conductors (a) Increases with the increase of temperature (b) Decreases with the increase of temperature (c) It does not depend on temperature (d) All of sudden changes at 400 K 47. Which of the following statement is correct (a) Liquids obey fully the ohm's law (b) Liquids obey partially the ohm's law (c) There is no relation between current and p.d. for liquids (d) None of the above 48. A certain piece of silver of given mass is to be made like a wire. Which of the following combination of length (L) and the area of cross-sectional (A) will lead to the smallest resistance (a) L and A (b) 2L and A/2 (c) L/2 and 2 A (d) Any of the above, because volume of silver remains same 49. The resistance of a wire is 10  . Its length is increased by 10% by stretching. The new resistance will now be (a) 12  (b) 1.2 (c) 13  (d) 11  50. Resistance of tungsten wire at 150 C is 133  . Its resistance temperature coefficient is 0.0045 / C . The resistance of this wire at 500 C will be (a) 180  (b) 225  (c) 258  (d) 317  51. A metal wire of specific resistance  ohm − cm −6 64 10 and length 198 cm has a resistance of 7 ohm, the radius of the wire will be (a) 2.4 cm (b) 0.24 cm (c) 0.024 cm (d) 24 cm 52. A copper wire of length 1 m and radius 1 mm is joined in series with an iron wire of length 2 m and radius 3 mm and a current is passed through the wires. The ratio of the current density in the copper and iron wires is (a) 18 : 1 (b) 9 : 1 (c) 6 : 1 (d) 2 : 3
53. For a metallic wire, the ratio V / i (V = the applied potential difference, i = current flowing) is (a) Independent of temperature (b) Increases as the temperature rises (c) Decreases as the temperature rises (d) Increases or decreases as temperature rises, depending upon the metal 54. The resistance of a wire is R. If the length of the wire is doubled by stretching, then the new resistance will be (a) 2R (b) 4R (c) R (d) 4 R 55. Which of the following has a negative temperature coefficient (a) C (b) Fe (c) Mn (d) Ag 56. The reciprocal of resistance is (a) Conductance (b) Resistivity (c) Voltage (d) None of the above 57. A solenoid is at potential difference 60 V and current flows through it is 15 ampere, then the resistance of coil will be (a) 4  (b) 8  (c) 0.25  (d) 2 58. All of the following statements are true except (a) Conductance is the reciprocal of resistance and is measured in Siemens (b) Ohm's law is not applicable at very low and very high temperatures (c) Ohm's law is applicable to semiconductors (d) Ohm's law is not applicable to electron tubes, discharge tubes and electrolytes 59. A potential difference of V is applied at the ends of a copper wire of length l and diameter d. On doubling only d, drift velocity (a) Becomes two times (b) Becomes half (c) Does not change (d) Becomes one fourth 60. If the resistance of a conductor is 5  at 50oC and 7  at 100oC then the mean temperature coefficient of resistance of the material is (a) 0.008/oC (b) 0.006/oC (c) 0.004/oC (d) 0.001/oC 61. The resistance of a discharge tube is (a) Ohmic (b) Non-ohmic (c) Both (a) and (b) (d) Zero 62. We are able to obtain fairly large currents in a conductor because (a) The electron drift speed is usually very large (b) The number density of free electrons is very high and this can compensate for the low values of the electron drift speed and the very small magnitude of the electron charge (c) The number density of free electrons as well as the electron drift speeds are very large and these compensate for the very small magnitude of the electron charge (d) The very small magnitude of the electron charge has to be divided by the still smaller product of the number density and drift speed to get the electric current 63. A platinum resistance thermometer has a resistance of 50  at 20C . When dipped in a liquid the resistance becomes 76.8  . The temperature coefficient of resistance for platinum is =  C − 3.92 10 / 3  . The temperature of the liquid is (a) 100 C (b) 137 C (c) 167 C (d) 200 C 64. In a wire of circular cross-section with radius r, free electrons travel with a drift velocity V when a current I flows through the wire. What is the current in another wire of half the radius and of the same material when the drift velocity is 2V (a) 2I (b) I (c) I / 2 (d) I / 4 65. The resistivity of a wire depends on its (a) Length (b) Area of cross-section (c) Shape (d) Material 66. The conductivity of a superconductor is (a) Infinite (b) Very large (c) Very small (d) Zero 67. In a neon discharge tube +  Ne 18 2.9 10 ions move to the right each second while 18 1.2 10 electrons move to the left per second. Electron charge is C 19 1.6 10 −  . The current in the discharge tube (a) 1 A towards right (b) 0.66 A towards right (c) 0.66 A towards left (d) Zero 68. A steady current flows in a metallic conductor of non-uniform cross-section. The quantity/ quantities constant along the length of the conductor is/are (a) Current, electric field and drift speed