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

Total Questions: 50

41. Keeping the potential difference constant, the resistance of a circuit is halved. What happens to the current? [RRB JE 26/05/2019 (Afternoon)]

Correct Answer: (d) It gets doubled
Solution:

42. If the potential difference across the ends of a conductor is halved, what happens to the current flowing through it? [RRB JE 27/05/2019 (Morning)]

Correct Answer: (d) It gets halved
Solution:

According to Ohm's law, potential difference is directly proportional to current in the circuit. (V ∝ I) ⇒ V = IR (where R is resistance), if potential difference is doubled across the ends of a conductor then the current flowing through the conductor also gets doubled.

43. How much work is done in moving 2 Coulombs of charge across two points having a potential difference of 12 V? [RRB JE 27/05/2019 (Morning)]

Correct Answer: (b) 24 Joule
Solution:

The potential difference across the two points is directly proportional to the work done per unit charge. ⇒ V = 𝑊/𝑄 where V is the potential  difference, W is work done and Q is the charge.
⇒ W = Q × V Given Q = 2 Coulombs, Voltage (V) = 12 V. ⇒ W = 2 × 12 = 24 Joule.

44. If the potential difference across the ends of a conductor is doubled, what happens to the current flowing through it ? [RRB JE 29/05/2019 (Morning)]

Correct Answer: (a) It gets doubled
Solution:

By Ohm's law, - Voltage, V = current(I) x resistance (R). V = IR.

45. A current of 5 Amperes flows around a circuit for 10 seconds. How much charge flows past a point in the circuit in this time? [RRB JE 29/05/2019 (Afternoon)]

Correct Answer: (d) 50 Columbs
Solution:

Given that, Current (I) = 5A, Time (T) = 10s, Charge (Q) = ? We know that charge (Q) = Current(I) × Time(T) ⇒ Q = 5 × 10 ⇒ 50 Columbs.

46. Three 2 V cells are connected in series and used as a battery in a circuit. What is the potential difference at the terminals of the battery ? [RRB JE 31/05/2019 (Morning)]

Correct Answer: (a) 6 volt
Solution:

Given one cell potential difference (p.d) = 2V In series connection Potential differences across terminal is sum of all cell potential difference So, Total p.d = 2 + 2 + 2 = 6V.

47. If the length of a wire is doubled by taking more of the wire, what happens to its resistance? [RRB JE 01/06/2019 (Evening)]

Correct Answer: (c) Gets doubled
Solution:

Resistance : A measure of the opposition to current flow in an electrical circuit. Measured in ohms (Ω). Resistance (R) = ρ𝑙/𝐴 Where ρ is the resistivity of a conductor, l is the length of the conductor and A is the cross-sectional area. If the length of the wire will get doubled then new resistance (Rⁱ ) will be Rⁱ = ρ 2𝑙/A  ⇒ Rⁱ  = 2 R.

48. _______ is the amount of work done in carrying a charge of 4C across two points having a potential difference of 18V. [RRB Group D 17/09/2018 (Morning)]

Correct Answer: (b) 72 J
Solution:

Given, Charge (q) = 4 C, potential difference (V) = 18 V
Since, Work done to carry a charge (W) = Charge (q) × Potential difference (V), ⇒ W = 4 × 18 ⇒ W = 72 J.

49. If the current flowing through a circuit is 0.6 A for 6 mins, the amount of electric charge flowing through it is _____. [RRB Group D 17/09/2018 (Afternoon)]

Correct Answer: (b) 216 C
Solution:

Given : Current (I) = 0.6 A, Time (t) = 6 min, Charge (Q) = ?
∵ Charge = I × t = 0.6 × (6 × 60) = 216 ampere - second = 216 C.

50. An electric lamp of 120 W is used for 8 hours per day. Calculate the units of energy consumed by the lamp in one day. [RRB Group D 18/09/2018 (Morning)]

Correct Answer: (c) 0.96 uni
Solution:

Given : Electric lamp (power) = 120 W; Total time taken by lamp = 8 hours/day.
Power (P) = E/t
120 = E/8
E = 960 watt- hours = 0.96 kWh or 0.96 units.