Current Electricity PYQs Set 3 (PDF)

Set 3 of 25 · Questions 61-90 of 723

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Mere Teacher · Previous Year Questions JEE Main Physics · Current Electricity · Set 3 (Q61-90)
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61. $In a meter bridge experiment, when a nichrome wire is in the right gap, the balancing length is 60 cm . When the nichrome wire is uniformly stretched to increase its length by 20 % and again connected in the right gap, the new balancing length is nearly$ (1) $61 cm$ (2) $31 cm$ (3) $51 cm$ (4) $41 cm$ 62. $The resistivity of a metal is 1 \times 10^{- 8} Ωm . If it contains 9 \times 10^{28} electrons per m^{3} then the relaxation time of electrons inside the metal is nearly (electron mass = 9 \times 10^{- 31} kg)$ (1) $4 \times 10^{- 14} s$ (2) $7 \times 10^{- 14} s$ (3) $1.0 \times 10^{- 14} s$ (4) $9 \times 10^{- 14} s$ 63. $If voltage across a bulb rated 220 V, 100 W drops by 2.5 % of its rated value, the percentage of the rated value by which the power would decrease is$ (1) $5 %$ (2) $20 %$ (3) $10 %$ (4) $2.5 %$ 64. $Two conductors have the same resistance at 0ºC but their temperature coefficients of resistance are α_{1} and α_{2} . The respective temperature coefficients of their series and parallel combinations are nearly$ (1) $\frac{α _{1} + α _{2}}{2}, α_{1} + α_{2}$ (2) $α_{1} + α_{2}, \frac{α _{1} + α _{2}}{2}$ (3) $α_{1} + α_{2}, \frac{α _{1} α _{2}}{α _{1} + α _{2}}$ (4) $\frac{α _{1} + α _{2}}{2}, \frac{α _{1} + α _{2}}{2}$ 65. $A wire of resistance 160 Ω is melted and drawn in a wire of one-fourth of its length. The new resistance of the wire will be$ (1) $16 Ω$ (2) $10 Ω$ (3) $640 Ω$ (4) $40 Ω$ 66. $The drift velocity of electrons in a conducting wire connected to a cell is V_{d} . If the length of the wire is doubled and area of cross-section is halved then the drift velocity of electrons becomes.$ (1) $V_{d}$ (2) $V_{d} 2$ (3) $2 V_{d}$ (4) $4 V_{d}$ 67. $To verify Ohm's law, a student is provided with a test resistor R_{T}, a high resistance R_{1}, a small resistance R_{2}, two identical galvanometers G_{1} and G_{2}, and a variable voltage source V. The correct circuit to carry out the experiment is:$ (1) (2) (3) (4) 68. $A set of n equal resistors, of value R each, are connected in series to a battery of emf E and internal resistance R. The current drawn is I. Now, the n resistors are connected in parallel to the same battery. Then the current drawn from battery becomes 10I. The value of n is$ (1) $10$ (2) $11$ (3) $20$ (4) $9$ 69. $For the two cells having same EMF E and internal resistance r, the current passing through the external resistor 6Ω is same when both the cells are connected either in parallel or in series. The value of internal resistance r is____Ω .$ (1) $6$ (2) $3$ (3) $4$ (4) $9$ 70. $Masses of three wires of copper are in the ratio 1 : 3 : 5 and their lengths are in the ratio 5 : 3 : 1 . The ratio of their electrical resistance are$ (1) $1 : 15 : 125$ (2) $1 : 3 : 5$ (3) $125 : 15 : 1$ (4) $5 : 3 : 1$ 71. $Ten identical cells each of emf 2 V and internal resistance 1Ω are connected in series with two cells wrongly connected. A resistor of 10Ω is connected to the combination. What is the current through the resistor?$ (1) $1.8 A$ (2) $2.4 A$ (3) $0.6 A$ (4) $1.2 A$ 72. $A wire of a certain material is stretched slowly by 10 % . Its new resistance and specific resistance becomes respectively$ (1) $1.21 times, same$ (2) $1.1 times, 1.1 times$ (3) $both remains the same$ (4) $1.2 times, 1.1 times$ 73. $Which of the following physical quantities have the same dimensions?$ (1) $Electric displacement (D) and surface charge density$ (2) $Displacement current and electric field$ (3) $Current density and surface charge density$ (4) $Electric potential and energy$ 74. $In a meter bridge, the balancing length from the left end (standard resistance of one ohm is in the right gap) is found to be 20 cm. The value of the unknown resistance is$ (1) $0.8 Ω$ (2) $0.5 Ω$ (3) $0.4 Ω$ (4) $0.25 Ω$ 75. $A constant potential difference is applied between the ends of the wire. If the length of the wire is elongated 4 times, then the drift velocity of electrons will be$ (1) $increases 4 times$ (2) $decreases 4 times$ (3) $increases 2 times$ (4) $decreases 2 times$ 76. $When moving coil galvanometer (MCG) is converted into a voltmeter, the series resistance is ' n' times the resistance of galvanometer. How many times that of MCG the voltmeter is now capable of measuring voltage?$ (1) $n$ (2) $n + 1 n$ (3) $n + 1$ (4) $n - 1$ 77. $A charged particle is moving in an electric field of 3 \times 10^{- 10} V m^{- 1} with mobility 2.5 \times 10^{6} m^{2} / Vs, its drift velocity is$ (1) $2.5 \times 10^{4} m / s$ (2) $7.5 \times 10^{- 4} m / s$ (3) $1.2 \times 10^{- 4} m / s$ (4) $8.33 \times 10^{- 4} m / s$ 78. $Copper and Germanium are cooled from room temperature to 100 K . Then the resistance of$ (1) $Germanium decreases, Copper increases$ (2) $Germanium decreases, Copper decreases$ (3) $Germanium increases, Copper decreases$ (4) $Germanium increases, Copper increases.$ 79. $Current sensitivity of a moving coil galvanometer is 5 div/mA and its voltage sensitivity (angular deflection per unit voltage applied) is 20 div/V. The resistance of the galvanometer is:$ (1) $40$ (2) $500$ (3) $250$ (4) $25$ 80. $The electron drift speed is small and the charge of the electron is also small but still, we obtain large current in a conductor. This is due to$ (1) $the conducting property of the conductor$ (2) $the resistance of the conductor is small$ (3) $the electron number density of the conductor is small$ (4) $the electron number density of the conductor is enormous.$ 81. $The potentiometer is best for measuring voltage, as$ (1) $it has a sensitive galvanometer and gives null deflection$ (2) $it has wire of high resistance$ (3) $it measures p . d . in closed circuit$ (4) $it measures p.d in open circuit.$ 82. $The internal resistance of a cell of e.m.f. 2 V is 0.1 Ω . It is connected to a resistance of 3.9 Ω . me voltage across the cell will be$ (1) $1.95 V$ (2) $1.9 V$ (3) $0.5 V$ (4) $2 V$ 83. $The resistances in left and right gap of a meter bridge are 20Ω and 30Ω respectively. When the resistance in the left gap is reduced to half its value, the balance point shifts by$ (1) $15 cm to the right$ (2) $15 cm to the left$ (3) $20 cm to the right$ (4) $20 cm to the left$ 84. $For a given electric current the drift velocity of conduction electrons in a copper wire is v_{d} and their mobility is µ. When the current is increased at constant temperature$ (1) $v_{d} increases, µ remains the same$ (2) $v_{d} remains the same, µ increases$ (3) $v_{d} decreases, µ remains the same$ (4) $v_{d} remains the same, µ decreases$ 85. $Three equal resistors connected in series across a source of e.m.f. together dissipate 10 watt of power. What will be the power dissipated in watt if the same resistors are connected in parallel across the same source of e.m.f.?$ (1) $30$ (2) $\frac{10}{3}$ (3) $10$ (4) $90$ 86. $A 200Ω resistor has a certain color code. If one replaces the red color by green in the code, the new resistance will be:$ (1) $100Ω$ (2) $400Ω$ (3) $300Ω$ (4) $500Ω$ 87. $Resistance n, each of r ohm, when connected in parallel give an equivalent resistance of R ohm. If these resistances were connected in series, the combination would have a resistance in ohms, equal to$ (1) $n^{2} R$ (2) $R / n^{2}$ (3) $R / n$ (4) $nR$ 88. $Which of the following acts as a circuit protection device? [NEET 2019]$ (1) $Inductor$ (2) $Switch$ (3) $Fuse$ (4) $Conductor$ 89. $A galvanometer coil has 500 turns and each turn has an average area of 3 \times 10^{- 4} m^{2} . If a torque of 1.5 Nm is required to keep this coil parallel to a magnetic field when a current of 0.5 A is flowing through it, the strength of the field (in T) is \dots\dots\dots\dots$ 90. $A hollow cylindrical conductor has length of 3.14 m, while its inner and outer diameters are 4 mm and 8 mm respectively. The resistance of the conductor is n x 10-3 Ω .If the resistivity of the material is 2.4 x 10-8 Ω m. The value of n is$