Title CURRENT ELECTRICITY-1.pdf ✅

CHAPTER CURRENT ELECTRICITY 3 Exercise 1: NCERT Based Topic-wise MCQs 3.1 INTRODUCTION 1. Lighting is a phenomenon in which charges flow NCERT Page- 93 / N-81 (a) from the clouds to the earth (b) from the earth to the cloud (c) both (a) and (b) (d) none of these 3.2 ELECTRIC CURRENT 2. The amount of charge Q passed in time t through a crosssection of a wire is Q = 5t 2 + 3t + 1. The value of current at time t = 5s is NCERT / Page-94/ N-82 (a) 9A (b) 49A (c) 53A (d) None of these 3.3 ELECTRIC CURRENTS IN CONDUCTORS 3. When no current is passed through a conductor, NCERT Page-95 / N-83 (a) the free electrons do not move (b) the average speed of a free electron over a large period of time is not zero (c) the average velocity of a free electron over a large period of time is zero (d) the average of the velocities of all the free electrons at an instant is non zero 4. A current passes through a resistor. If K1 and K2 represent the average kinetic energy of the conduction electrons and the metal ions respectively then NCERT Page-95 / N-83 (a) K1 < K2 (b) K1 = K2 (c) K1 > K2 (d) any of these three may occur 3.4 OHM’S LAW 5. In the equation AB = C, A is the current density, C is the electric field, ThenB is NCERT Page-95 / N-83 (a) resistivity (c) potential difference (b) conductivity (d) resistance 6. The electric resistance of a certain wire of iron is R. If its length and radius are both doubled, then
(a) the resistance and the specific resistance, will both remain unchanged NCERT Page-96 / N-84 (b) the resistance will be doubled and the specific resistance will be halved (c) the resistance will be halved and the specific resistance will remain unchanged (d) the resistance will be halved and the specific resistance will be doubled 7. If negligibly small current is passed though a wire of length 15m and resistance of 5Ω, having uniform cross section of 6 × 10−7m2 , then coefficient of resistivity of material is NCERT Page-96 / N-84 (a) 1 × 10−7Ω − m (b) 2 × 10−7Ω − m (c) 3 × 10−7Ω − m (d) 4 × 10−7Ω − m 8. A wire X is half the diameter and half the length of a wire Y of similar material. The ratio of resistance of X to that of Yis NCERT Page-96 / N-84 (a) 8: 1 (b) 4: 1 (c) 2: 1 (d) 1: 1 9. An electric current is passed through a circuit containing two wires of same material, connected in parallel. If the lengths and radii of the wires are in the ratio of 3: 2 and 2: 3, then the ratio of the current passing through the wire will be NCERT Page-96 / N-84 | CBSE Sample 2021-2022 (a) 2: 3 (b) 3: 2 (c) 8: 27 (d) 27: 8 10. A wire of resistance R1 is drawn out so that its length is increased by twice of its original length. The ratio of new resistance to original resistance is: NCERT Page-96 / N-84 (a) 9: 1 (b) 1: 9 (c) 4: 1 (d) 3: 1 11. A wire of a certain material is stretched slowly by ten per cent. Its new resistance and specific resistance become respectively: NCERT Page-96 / N-84 (a) 1.2 times, 1.3 times (b) 1.21 times, same (c) both remain the same (d) 1.1 times, 1.1 times 12. The length of a given cylindrical wire is increased by 100%. Due to the consequent decrease in diameter the change in the resistance of the wire will be NCERT Page-97 / N-84 (a) 200% (b) 100% (c) 50% (d) 300% 13. The masses of the three wires of copper are in the ratio of 1: 3: 5 and their lengths are in the ratio of 5: 3: 1. The ratio of their electrical resistance is NCERT Page- 96 / N-84 (a) 1: 3: 5 (b) 5: 3: 1 (c) 1: 25: 125 (d) 125: 45: 3
14. A uniform wire of length l and radius r has a resistance of 100Ω. It is recast into a wire of radius r 2 . The resistance of new wire will be NCERT Page-96 / N-84 (a) 1600Ω (b) 400Ω (c) 200Ω (d) 100Ω 15. An electron beam has an aperture 1.0mm2 . A total of 6 × 1016 electrons go through any perpendicular cross section per second. Find the current density in the beam. (in A/m2 ) NCERT Page- 97/N-85 (a) 9.1 × 1013 (b) 9.6 × 103 (c) 6.6 × 105 (d) 8.6 × 1011 3.5 DRIFT OF ELECTRONS AND THE ORIGIN OF RESISTIVITY 16. A. The drift velocity of electrons decreases with the increase in the temperature of conductor. B. The drift velocity is inversely proportional to the area of cross-section of given conductor. C. The drift velocity does not depend on the applied potential difference to the conductor. D. The drift velocity of electron is inversely proportional to the length of the conductor. E The drift velocity increases with the increase in the temperature of conductor. Choose the correct answer from the options given below: NCERT Page-98 / N-86 (a) A and B only (b) A and D only (c) B and E only (d) B and C only 17. When a potential difference V is applied across a conductor at a temperature T, the drift velocity of electrons is proportional to NCERT Page-98 / N-86 (a) √V (b) V (c) √T (d) T 18. For which of the following dependence of drift velocity vd on electric field E, is Ohm's law obeyed? (a) vd ∝ E 2 NCERT Page-98 / N-86 (b) vd = E 1/2 (c) vd = constant (d) vd = E 19. A metal wire is subjected to a constant potential difference. When the temperature of the metal wire increases, the drift velocity of the electron in it NCERT Page-97 / N-85 (a) increases, thermal velocity of the electron increases (b) decreases, thermal velocity of the electron increases (c) increases, thermal velocity of the electron decreases (d) decreases, thermal velocity of the electron decreases 20. We are able to obtain fairly large currents in a conductor because NCERT Page-98 / N-86 (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 21. Two wires A and B of the same material, having radii in the ratio 1: 2 and carry currents in the ratio 4: 1. The ratio of drift speed of electrons in A and B is NCERT Page-98 / N-86 (a) 16: 1 (b) 1: 16 (c) 1: 4 (d) 4: 1 22. When a current I is set up in a wire of radius r; the drift velocity is vd. If the same current is set up through a wire of radius 2r, the drift velocity will be NCERT Page-98 / N-86 (a) 4vd (b) 2vd (c) vd/2 (d) vd/4 23. If the potential difference V applied across a conductor is increased to 2V. with its temperature kept constant, the drift velocity of the free electrons in a conductor will- NCERT Page-97 / N-86 | CBSE Sample 2021-2022 (a) remain the same. (b) become half of its previous value. (c) be double of its initial value. (d) become zero. 24. The number of free electrons per 100mm of ordinary copper wire is 2 × 1021. Average drift speed of electrons is 0.25 mm/s. The current flowing is NCERT Page-97/ N-86 (a) 5A (b) 80A (c) 8A (d) 0.8A 25. At room temperature, copper has free electron density of 8.4 × 1028perm3 . The copper conductor has a cross- section of 10−6m2 and carries a current of 5.4A. The electron drift velocity in copper is NCERT Page-98 / N-86 (a) 400m/s (b) 0.4m/s (c) 0.4mm/s (d) 72m/s 44. A battery of e.m.f.10V and internal resistance 0.5Ω is connected across a variable resistance R. The value of R for which the power delivered in it is maximum is given by NCERT Page-106 / N-93 (a) 0.5Ω (b) 1.0Ω (c) 2: 0Ω (d) 0.25Ω