Current Electricity PYQs Set 1 (PDF)

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Mere Teacher · Previous Year Questions JEE Main Physics · Current Electricity · Set 1 (Q1-30)
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1. $What equal length of an iron wire and a copper-nickel alloy wire, each of 2mm diameter connected parallel to give an equivalent resistance of 3Ω ? (Given resistivities of iron and copper-nickel alloy wire are 12 μΩ cm and 51 μΩ cm respectively)$ (1) $82m$ (2) $97m$ (3) $110m$ (4) $90m$ 2. $The Kirchhoff’s first law (\sum i = 0) and second law (\sum iR = \sum E), where the symbols have their usual meanings, are respectively based on$ (1) $conservation of charge, conservation of energy$ (2) $conservation of charge, conservation of momentum$ (3) $conservation of energy, conservation of charge$ (4) $conservation of momentum, conservation of charge$ 3. $When three identical bulbs of 60 watt, 200 volt rating are connected in series to a 200 volt supply, the power drawn by them will be$ (1) $60 watt$ (2) $180 watt$ (3) $10 watt$ (4) $20 watt$ 4. $Two cities are 150 km apart. Electric power is sent from one city to another city through copper wires. The fall of potential per km is 8 volt and the average resistance per km is 0.5 Ω . The power loss in the wire is$ (1) $19.2 W$ (2) $19.2 kW$ (3) $19.2 J$ (4) $12.2 kW$ 5. $A wire of resistance 4 Ω is stretched to twice its original length. The resistance of stretched wire would be:$ (1) $4$ (2) $8$ (3) $16$ (4) $2$ 6. $If the last band on the carbon resistor is absent, then the tolerance is$ (1) $5 %$ (2) $20 %$ (3) $10 %$ (4) $15 %$ 7. $When 5V potential difference is applied across a wire of length 0.1 m, the drift speed of electrons is 2.5 \times 1 0^{-4} m s^{-1} . If the electron density in the wire is 8 \times 1 0^{28} m^{-3}, the resistivity of the material is close to:$ (1) $1.6 \times 1 0^{- 8} Ωm$ (2) $1.6 \times 1 0^{- 7} Ωm$ (3) $1.6 \times 1 0^{- 6} Ωm$ (4) $1.6 \times 1 0^{- 5} Ωm$ 8. $A conductor wire having 10^{29} free electrons / m^{3} carries a current of 20 A . If the cross-section of the wire is 1 mm^{2}, then the drift velocity of electrons will be (e = 1.6 \times 10^{- 19} C)$ (1) $1.25 \times 10^{- 4} m s^{- 1}$ (2) $1.25 \times 10^{- 3} m s^{- 1}$ (3) $1.25 \times 10^{- 5} m s^{- 1}$ (4) $6.25 \times 10^{- 3} m s^{- 1}$ 9. $The charge flowing through a resistance R varies with time t as Q = at - b t^{2}, where a and b are positive constants. The total heat produced in R is:$ (1) $\frac{a ^{3} R}{b}$ (2) $\frac{a ^{3} R}{6 b}$ (3) $\frac{a ^{3} R}{3 b}$ (4) $\frac{a ^{3} R}{2 b}$ 10. $Two heaters A and B have power rating of 1 kW and 2 kW respectively. Those two are first connected in series and then in parallel to a fixed power source. The ratio of power outputs for these two cases is [NEET 2024]$ (1) $1 : 1$ (2) $2 : 9$ (3) $1 : 2$ (4) $2 : 3$ 11. $Three resistances each of 4 Ω are connected to form a triangle. The resistance between any two terminals is$ (1) $12 Ω$ (2) $2 Ω$ (3) $6 Ω$ (4) $8/3 Ω$ 12. $A current of 200 μA deflects the coil of a moving coil galvanometer through 60^{\circ} . The current to cause deflection through \frac{π}{10} radian is:$ (1) $30 μA$ (2) $120 μA$ (3) $60 μA$ (4) $180 μA$ 13. $A heating coil is labelled 100 W, 220 V The coil is cut in half and the two pieces are joined in parallel to the same source. The energy now liberated per second is$ (1) $200 W$ (2) $400 W$ (3) $25 W$ (4) $50 W$ 14. $A wire of resistance 4 Ω is stretched to twice its original length. The resistance of stretched wire would be$ (1) $8 Ω$ (2) $16 Ω$ (3) $2 Ω$ (4) $4 Ω$ 15. $A set of n equal resistors, of value R each are connected in series to a battery of emf E and internal resistance R. The current drawn is I. Now, the n resistors are connected in parallel to the same battery. Then, the current drawn from battery becomes 10I. The value of n is [NEET 2018]$ (1) $20$ (2) $11$ (3) $10$ (4) $9$ 16. $In a large building, there are 15 bulbs of 40W, 5 bulbs of 100 W, 5 fans of 80 W and 1 heater of 1 kW. The voltage of the electric mains is 220 V. The minimum capacity of the main fuse of the building will be:$ (1) $8 A$ (2) $10 A$ (3) $12 A$ (4) $14 A$ 17. $A current of 5A is passing through a non-linear magnesium wire of cross-section 0. 04 m^{2} . At every point the direction of current density is at an angle of 600 with the unit vector of area of cross-section. The magnitude of electric field at every point of the conductor is: (Resistivity of magnesium ρ = 44 \times 1 0^{- 8} Ωm)$ (1) $11 \times 1 0^{- 2} V / m$ (2) $11 \times 1 0^{- 7} V / m$ (3) $11 \times 1 0^{- 5} V / m$ (4) $11 \times 1 0^{- 3} V / m$ 18. $The resistivity of potentiometer wire is 40 \times 10^{- 8} Ωm metre and its area of cross-section is 8 \times 10^{- 6} m^{2} . If 0.2 ampere current is flowing through the wire, the potential gradient of the wire is$ (1) $10^{- 1} V / m$ (2) $10^{- 2} V / m$ (3) $10^{- 3} V / m$ (4) $10^{- 4} V / m$ 19. $Two resistances are connected in the two gaps of a meter bridge. The balancing point is obtained at 20 cm . When a resistance of 15Ω is connected in series with the smaller resistance of the two, the balancing point shifts to 40 cm . The value of smaller resistance is$ (1) $9Ω$ (2) $12Ω$ (3) $6Ω$ (4) $3Ω$ 20. $Two bulbs of (40 W, 200 V), and (100 W, 200 V) . Then correct relation for their resistances$ (1) $R_{40} < R_{100}$ (2) $R_{40} > R_{100}$ (3) $R_{40} = R_{100}$ (4) $no relation can be predicted.$ 21. $A resistor has a colour code of green, blue, brown and silver. What is its resistance?$ (1) $56Ω \pm 5 %$ (2) $560Ω \pm 10 %$ (3) $560Ω \pm 5 %$ (4) $5600Ω \pm 10 %$ 22. $Water boils in an electric kettle in 20 minutes after being switched on. Using the same main supply, the length of the heating element should be_____to ____times of its initial length if the water is to be boiled in 15 minutes.$ (1) $decreased, 3/4$ (2) $increased, 4/3$ (3) $decreased, 4/3$ (4) $increased, 3/4$ 23. $The resistances of the four arms P, Q, R and S in a Wheatstone’s bridge are 10 ohm, 30 ohm, 30 ohm and 90 ohm, respectively. The e.m.f. and internal resistance of the cell are 7 Volt and 5 ohm respectively. If the galvanometer resistance is 50 ohm, the current drawn from the cell will be:$ (1) $0.2 A$ (2) $0.1 A$ (3) $2.0 A$ (4) $1.0 A$ 24. $40 electric bulbs are connected in series across a 220 V supply. After one bulb is fused the remaining 39 are connected again in series across the same supply The illumination will be$ (1) $more with 40 bulbs than with 39$ (2) $more with 39 bulbs than with 40$ (3) $equal in both the cases$ (4) $in the ratio 4 0^{2} : 3 9^{2}$ 25. $If two bulbs, whose resistances are in the ratio of 1 : 2 are connected in series, the power dissipated in them has the ratio of$ (1) $2 : 1$ (2) $1 : 4$ (3) $1 : 1$ (4) $1 : 2.$ 26. $Two conductors have the same resistance at 0^{\circ} C but their temperature coefficients of resistance are α_{1} and α_{2} . The respective temperature coefficients of their series and parallel combinations are nearly$ (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) $\frac{α _{1} + α _{2}}{2}, \frac{α _{1} + α _{2}}{2}$ 27. $A current of 2 mA was passed through an unknown resistor which dissipated a power of 4.4 W. Dissipated power when an ideal power supply of 11V is connected across it is:$ (1) $11 \times 1 0^{-4} W$ (2) $11 \times 1 0^{5} W$ (3) $11 \times 1 0^{-3} W$ (4) $11 \times 1 0^{-5} W$ 28. $If voltage across a bulb rated 220 volt‐ 100 watt drops by 2.5% of its rated value, the percentage of the rated value by which the power would decrease is$ (1) $20%$ (2) $2.5%$ (3) $5%$ (4) $10%$ 29. $A uniform heating wire of resistance 36Ω is connected across a potential difference of 240V. The wire is then cut into half and potential difference of 240V is applied across each half separately. The ratio of power dissipation in first case to the total power dissipation in the second case would be 1:x, where x is...........$ 30. $A resistor develops 300 J of thermal energy in 15s, when a current of 2A is passed through it. If the current increases to 3A, the energy developed in 10s is_________J.$