Railway Science (Physics-Electric Current and its Effects) (Part-VI)

Total Questions: 50

21. Two identical bulbs are connected in parallel to a battery of 4 V. If the current in the circuit is 0.2 A, the power dissipated by the battery is: [RRC Group D 08/09/2022 (Morning)]

Correct Answer: (b) 0.8 W
Solution:

We know, Power is given as the product of voltage and current.
So, P = V × I. Given Voltage = 4 V, I = 0.2 A
P = 4 × 0.2 = 0.8 Watt.

22. Two identical resistors are connected in parallel to a 6 V battery. The total power dissipated in the circuit is 12 W. The current in each resistor is: [RRC Group D 08/09/2022 (Afternoon)]

Correct Answer: (d) 1.0 A
Solution:

Power, P = V × I where, V = Voltage and I = Current
Current in the circuit, I = p/v  = 12/6 = 2 A
Since, current across each identical resistors in parallel combination gets equally divided So, Iᵣ = 1A

23. Consider two wires, A and B, of same thickness but lengths L and 5L, respectively. If the resistances of A and B are 1.0Ω and 2.5Ω , respectively, the ratio of the resistivity of A to the resistivity of B is: [RRC Group D 08/09/2022 (Afternoon)]

Correct Answer: (d) 2
Solution:

24. A 4Ω resistor, A. is connected in series to a 6Ω resistor, B, and a 2 V battery. The potential drops across A and B are respectively_____________. [RRC Group D 08/09/2022 (Evening)]

Correct Answer: (d) 0.8 V and 1.2 V
Solution:

25. Resistance of a conducting wire is 15 ohm. If another wire of the same material and length but having one-third radius is taken, then the resistance of the second wire will be ___. [RRC Group D 09/09/2022 (Evening)]

Correct Answer: (d) 135 ohm
Solution:

Formula used, R = ρL/A where, R (resistance of the wire), ρ (resistivity of the material of wire), L (length of the wire) and A (cross sectional area of the wire).

26. The resistance of a wire of length L and area of cross-section A is 0.4Ω. The resistance of a wire of the same material, of the same length (L) and area of cross-section 4A will be: [RRC Group D 12/09/2022 (Morning)]

Correct Answer: (d) 0.1 Ω
Solution:

27. A copper wire AB is made of three parts, AC, CD and DB of resistances in the ratio of 2:3:4. The wire is connected to a battery. If V₁. V₂ and 𝑉₃ are the potential drops across AC, CD and DB, respectively, then which of the following is correct? [RRC Group D 12/09/2022 (Afternoon)]

Correct Answer: (c) 𝑉₁ : 𝑉₂ : 𝑉₃ = 3 : 4 : 2
Solution:

As per Ohm’s Law, V = IR. All three parts of wire (AC, CD, DB) can be considered to be connected in series. Therefore, Current = constant and voltage drop will be directly proportional to their resistances.

28. A 10Ω resistor, A, is connected in series to a 20Ω resistor, B, and a 6V battery. The potential drops across A and B are respectively___________. [RRC Group D 12/09/2022 (Evening)]

Correct Answer: (a) 2 V and 4 V
Solution:

29. If current is doubled and potential difference is reduced to half, then_______ [RRC Group D 13/09/2022 (Morning)]

Correct Answer: (c) resistance will become one-fourth
Solution:

30. The magnitudes of the magnetic field at a point at distance r from a straight conductor carrying current I, 2I and 3I, one by one, are B₁, B₂ and 𝐵₃ , respectively. Which of the following relations is correct? [RRC Group D 13/09/2022 (Afternoon)]

Correct Answer: (c) 𝐵₃ > 𝐵₂ > 𝐵₁
Solution: