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

Total Questions: 50

1. Two wires, A and B, are made of the same material, but the length of A is 3 times that of B, and the cross-section of A is 1/4th of that of B. The resistance of A is: [RRC Group D 18/09/2022 (Evening)]

Correct Answer: (c) 12 times that of B
Solution:

2. In a circuit, there are five resistors each of 5 Ω, and they are connected in such a way that the resistance of the circuit is the maximum. Now this circuit is connected to a battery of 15 V. The current flowing through the circuit is: [RRC Group D 18/09/2022 (Evening)]

Correct Answer: (c) 0.6 A
Solution:

3. In an electrical circuit four identical bulbs are connected in parallel to each other to a battery of 10 V (negligible internal resistance). When all the four bulbs glow, a current of 4 A is recorded. Then the power dissipated in the circuit and the resistance of each bulb are ______ and _____, respectively. [RRC Group D 19/09/2022 (Morning)]

Correct Answer: (b) 40 W, 10 Ω
Solution:

Given, R₁ = R₂ = R₃ = R₄ = R, V = 10 volt, I = 4 A.
P = VI ⇒ P = 10 ✕ 4 ⇒ P = 40 watt.

4. If the induced EMF in the coil of a conductor of resistance 10Ω is -2 V, then the induced current in the coil is: [RRC Group D 19/09/2022 (Afternoon)]

Correct Answer: (a) - 0.2 A
Solution:

Ohm's Law states that the current (I) through a conductor is equal to the voltage (V) across the conductor divided by its resistance (R). I = V/R
In this case, the induced EMF in the coil is given as -2 V, and the resistance of the conductor is 10 Ω.
I = (-2 V) / 10 Ω ⇒ I = -0.2 A
Therefore, the induced current in the coil is -0.2 A. The negative sign indicates that the current flows in the opposite direction to the direction of the induced EMF.

5. Suppose in a circuit, several electric lamps are required to be used on a 220 V electric supply line, and they are rated as 20 W. If the maximum allowable current is 10 A, then the number of lamps that can be connected in parallel with each other across the two wires of the 220 V line is: [RRC Group D 19/09/2022 (Evening)]

Correct Answer: (b) 110
Solution:

Voltage (V) = 220 V, Power (P) = 20 W, Maximum current allowed (I) = 10 A

6. What is the heat energy produced in a resistance of 10Ω when 5 A current flows through it for 5 minutes? [RRC Group D 19/09/2022 (Evening)]

Correct Answer: (a) 7.5 × 10⁴ J
Solution:

Given : Resistance (R) = 10 Ω, Current (I) = 5 A, Time (t) = 5 min = 300 s; Heat transfer (H) = I²Rt
H = (5)² × 10 × 300 ⇒ H = 75000 J
⇒ 7.5 × 10⁴ J.

7. Consider two circuits, A and B, [RRC Group D 19/09/2022 (Evening)]

Correct Answer: (b)
Solution:

8. If coil A of resistance 15Ω and coil B of resistance 5Ω are subjected to time varying magnetic field, then the current induced in these coils are: [RRC Group D 19/09/2022 (Evening)]

Correct Answer: (d) different
Solution:Now, Comparing equation 1 and 2, the ratio of equation 1 and 2 can not be the same or 1 then it will be different. Hence,the currents induced in these coils are different.

9. Suppose in a circuit, a silver wire of length L and cross-sectional area A is replaced by an aluminium wire of length 5L and cross-sectional area 9A. The resistance of the circuit will [RRC Group D 20/09/2022 (Morning)]

Correct Answer: (c) decrease to 0.9 times of itself
Solution:

10. Consider a wire of resistance 10 Ω If there is another wire of the same material and the same length as the previous one, but the cross-sectional area is double, then the resistance of the new wire is ? [RRC Group D 20/09/2022 (Morning)]

Correct Answer: (b) 5 Ω
Solution:

Resistance (R) = ⍴ × 𝐿/A where ⍴ = resistivity, l is length, A is Area of cross section.
Conditions I :  (R) = ⍴ × 𝐿/A Let A = 1;
10 Ω = ⍴ × 𝐿/1 ⇒ ⍴ = 10Ω/ 𝐿
Conditions II : Let A = 2
(R) = ⍴ × 𝐿/A (Since the same material is used, the resistivity will be the same)
= 10Ω/ 𝐿 × 𝐿/2 = 5 Ω