Tiêu đề 18. Current Electricity Med.pdf ✅

1. Ten million electrons pass from point P to point Q in one micro second. The current and its direction is (a) 1.6 × 10-14 A, from point P to point Q (b) 3.2 × 10-14 A, from point P to point Q (c) 1.6 × 10-6 A, from point Q to point P (d) 3.2 × 10-12 A, from point Q to point P 2. 1 ampere current is equivalent to (a) 6.25 × 1018 electrons s-1 (b) 2.25 × 10-18 electrons s-1 (c) 6.25 × 1014 electrons s-1 (d) 2.25 × 1014 electrons s-1 3. A current in a wire is given by the equation, I 2x 3t 1 2 = − + the charge through cross section of wire in time interval t = 3 s to t = 5 s is t = 5 s is (a) 32.33 C (b) 43.34 C (c) 45.5 C (d) 42 c 4. The current in a wire varies with time according to the equation I = 4 +2 t, where I is in ampere and t is in second. The quantity of charge which has to be passed through a cross-section of the wire during the time t = 2 s to t = 6 s is (a) 40 C (b) 48 C (c) 38 C (d) 43 C 5. In an atom electrons revolves around the nucleus along a path of radius 0.72 o A making 18 9.410 revolution per second. The equivalent current is (e 1.6 10 C) −19 =  (a) 1.2 A (b) 1.5 A (c) 1.4 A (d) 1.8 A 6. A charge is moving across a junction, then (a) Momentum will be conserved. (b) Momentum will not be conserved. (c) At some places momentum will be conserved and at some other places momentum will not be conserved. (d) None of these. 7. The direction of the flow of current through electric circuit is (a) From low potential to high potential. (b) From high potential to low potential. (c) Does not depend upon potential value. (d) Current cannot flow through circuit. 8. A wire of resistance 4 is used to wind a coil of radius 7 cm. The wire has a diameter of 1.4 mm and the specific resistance of its material is   −2 2 10 m. The number of turns in the coil is (a) 50 (b) 40 (c) 60 (d) 70 9. The electrical resistance of a conductor depends upon (a) Size of conductor (b) Temperature of conductor (c) Geometry of conductor (d) All of these 10. A cylindrical rod is reformed to half of its original length keeping volume constant. If its resistance before this change were R, then the resistance after reformation of rod will be (a) R (b) R/4 (c) 3R/4 (d) R/2 11. A wire with 15 resistance is stretched by one tenth of its original length and kept volume of wire is constant. Then its resistance will be (a) 15.18 (b) 81.15 (c) 51.18 (d) 18.15 12. Space between two concentric spheres of radii 1 r 1 r and 2 r ,such that 1 r < 2 r , is filled with a material of resistivity  . Find the resistance between inner and outer surface of the material. (a) r 2 r 2 1  (b)  −  r r 4 r r 1 2 2 1 (c)   r − r 4 r r 2 1 1 2 (d) None of these 13. Three resistors 2, 4 and 5 are combined in parallel. This combination is connected to battery of emf 20 V and negligible internal resistance. The total current drawn from the battery is (a) 10 A (b) 15 A (c) 19 A (d) 23 A 14. The voltage V and current I graphs for a conductor at two different temperatures T1 and T2 are shown in the figure. The relation between T1 and T2 is (a) T1  T2 (b) T1  T2 (c) T1 = T2 (d) 2 1 T 1 T =
15. A charged particle having drift velocity of 4 1 7.5 10 ms − −  in electric field of 10 1 3 10 V m − −  mobility is. (a) 6 2 1 1 6.5 10 m V s − − −  (b) 6 2 1 1 2.5 10 m V S − −  (c) 4 2 1 1 2.5 10 m V S − −  (d) 4 2 1 1 6.5 10 m V s − −  16. For which of the following dependences of drift velocity on electric field E, is Ohm’s law obeyed? (a) vd  E (b) 2 vd  E (c) vd  E (d) E 1 vd  17. Match the Column I with Column II. Column I Column II (A) Ohm’s law is applicable to (p) Metals (B) Ohm’s law is not applicable to (q) Greater resistivity (C) Alloys have (r) Diodes, electrolytes, semiconductors (a) A –r, B –q, C –p (b) A – p, B –r, C -q (c) A – r, B –p, C –q (d) A –q, B –r, C – p 18. Which of the following I-V graph represents ohmic conductors? (a) (b) (c) (d) 19. The I-V characteristics shown in figure represents (a) Ohmic conductors (b) Non-ohmic concuctors (c) Insulators (d) Superconductors 20. Two metal wires of identical dimensions are connected in series. If 1 and 2 and are the conductivities of the metals respectively, the effective conductivity of the combination is (a) 1 + 2 (b) 2 1 + 2 (c) 12 (d) 1 2 1 2 2  +    21. Which of the following is correct for V-1 graph a good conductor? (a) (b) (c) (d) 22. Arrange the following materials in increasing order of their resistivity,Nichrome, copper, Germanium Silicon (a) Copper27. The temperature dependence of the resistivity of a semiconductor is given by (a) (b) (c) (d) 28. What is the order of magnitude of the resistance of dry human body? (a) 10 (b) 10 k (c) 10M (d) 10 29. A resistor is marked with the rings coloured brown, black, green and gold. The resistance in ohm is (a) (3.5 10 5%) 5   (b) (1.10 10 10%) 5   (c) (8 10 5%) 6   (d) (1 10 5%) 6   30. Two cells 1  and 2  connected in opposition to each other as shown in figure. The cell 1  is of emf 9 V and internal resistance 3  the cell 2  is of emf 7 V and internal resistance 7  . The potential difference between the points A and B is (a) 8.4 V (b) 5.6 V (c) 7.8 V (d) 6.6 V 31. Nichrome or Manganin is widely used in wire bound standard resistors because of their (a) Temperature independent resistivity. (b) Very weak temperature dependent resistivity. (c) Strong dependence of resistivity with temperature. (d) Mechanical strength. 32. With increase in temperature the conductivity of (a) Metals increases and of semiconductor decreases. (b) Semiconductors increases and of metals decreases. (c) In both metals and semiconductors increase. (d) In both metal and semiconductor decreases. 33. The resistance of a heating element is 99  at room temperature. What is the temperature of the element if the resistance is found to be 116 ? (Temperature coefficient of the material of the resistor is 4 o 1 1.7 10 C − −  ) (a) 999.9C (b) 1005.3C (c) 1020.2C (d) 1037.1C 34. The resistance of the wire in the platinum resistance thermometer at ice point is 5  and at steam point is 5.25 . When the thermometer is inserted in an unknown hot bath its resistance is found to be 5.5 . The temperature of the hot bath is (a) 100 o C (b) 200 o C (c) 300 o C (d) 350 o C 35. A wire has a resistance of at 2.5  at 28 C o and a resistance of 2.9  at 100 C o . The temperature coefficient of resistivity of material of the wire is (a) 3 o 1 1.06 10 C − −  (b) 2 o 1 3.5 10 C − −  (c) 3 o 1 2.22 10 C − −  (d) 2 o 1 3.95 10 C − −  36. A heater coil is rated 100 W, 200 V. It is cut into two identical parts. Both parts are connected together in parallel, to the same source of 200 V. The energyl liberated per second in the new combination is (a)100 J (b) 200 J (c) 300 J (d) 400 J 37. Match the Column I with Column II. Column I Column II (A) Smaller the resistance greater thecurrent (p) If the same voltage is applied and resistance are in series (B) Greater or smaller the resistance the current is same (q) If the same currect is passed (C) Greater the resistance smaller the power (r) When resistances are connected in series (D) Greater the resistance greater the power (s) When resistances are connected in parallel (a) A - r, B - p, C - q, D – s (b) A - p, B - r, C - q, D – s (c) A - r, B - p, C - s, D – q (d) A - s, B - r, C - p, D – q 38. An electric heater is connected to the voltage supply After few seconds, current get its steady value then its initial current will be (a) Equal to its steady current (b) Slightly higher than its steady current (c) Slightly less than its steady current (d) Zero
39. In the series combination of two or more than two resistances. (a) The current through each resistance is same (b) The voltage through each resistance is same (c) Neither current nor voltage through each resistance is same (d) Both current and voltage through each resistance are same. 40. A wire of resistance 12 ohms per meter is bent to form a complete circle of radius 10 cm. The resistance between its two diametrically opposite points, A and B as shown in the figure is (a) 3  (b) 6 (c) 6 (d) 0.6 41. Combine three resistors 5  , 4.5  , and 3  in such a way that the total resistance of this combination is maximum (a) 12.5  (b) 13.5  (c) 14.5  (d) 16.5  42. Three resistors of resistances 3  , 4  and 5  are combined in parallel. This combination is connected to a battery of emf 12V and negligible internal resistance, current through each resistor in ampere is (a) 4, 3, 2.4 (b) 8, 7, 3.4 (c) 2, 5, 1.8 (d) 5, 5, 8.2 43. An infinite ladder network of resistance is constructed with 1  and 2  resistance as shown in figure. The 6V battery between A and B has negligible internal resistance. The equivalent resistance between A and B is (a) 1  (b) 2  (c) 3  (d) 4  44. The total resistance in the parallel combination of three resistance 9 7 , and 5  is (a) 1.22 (b) 2.29  (c) 4.22  (d) 2.02  45. A copper cylindrical tube has inner radius a and outer radius b. The resistivity is  . The resistance of the cylinder between the two ends is (a) 2 2 b a l −  (b) 2 (b a) l  −  (c) ( ) 2 2 b a l  −  (d) ( ) l b a 2 2   − 46. The equivalent resistance between A and B for the circuit shown in figure is (a) 13.1 (b) 15.1 (c) 17.1 (d) 19.1 47. n resistors each of resistance R first combine to give maximum effective resistance and then combine to give minimum effective resistance. The ratio of the maximum to minimum resistance is (a) n (b) 2 n (c) n 1 2 − (d) 3 n 48. Equivalent resistance of the given network is (a) 28 (b) 18 (c) 26 (d) 25 49. The correct combination of three resistances 1 ,2 and 3 to get equivalent resistance  5 11 is (a) All three are combines in parallel (b) All three are combine in series (c) 1  and 2  in parallel and 3  is in series to both (d) 2  and 3  are combined in parallel and 1  is in series to both 50. The equivalent resistance of series combination of four equal resistors is S. If they are joined in parallel, the total resistance if P. The relation between S and P is given by S=nP. Then the minimum possible value of n is (a) 12 (b) 14 (c) 16 (d) 10 51. Which arrangement of 3  resistors will given a total resistance of 7  ? (a) (b)