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

Total Questions: 50

31. Which of the following is an INCORRECT formula for electric power? [RRC Group D 13/09/2022 (Afternoon)]

Correct Answer: (a) P = 𝑉/𝐼
Solution:

According to ohm’s law V = IR ---(1)
and The electric power is given by P = VI -----(2)
where, V is the potential difference, I is the electric current and P is the electric power Putting value of V from equation 1 to equation 2,
P = I²R
Putting the value of I (I = V/R ) from
equation (1) to equation (2)
P = V²/R

32. Two resistors, each of 20Ω, are connected in parallel. The combination, in turn, is connected in series to a third resistor of 20Ω and a battery of 3 V. The power supplied by the battery is: [RRC Group D 13/09/2022 (Evening)]

Correct Answer: (d) 0.30 W
Solution:

33. If the current and potential difference are tripled in a circuit, keeping the resistance constant, then power will increase: [RRC Group D 14/09/2022 (Morning)]

Correct Answer: (d) nine fold
Solution:

Power = Rate at which work is done or energy is transferred per unit time. Power (P) = VI ; where v = potential difference, I = current; P’ = V’I’ = 3V × 3I = 9VI = 9P.

34. If the induced current in the coil of a conductor of resistance 4 Ω is 1 mA, then EMF induced in the coil is: [RRC Group D 14/09/2022 (Morning)]

Correct Answer: (c) 4 mV
Solution:

I = E/R, E = IR, E = 4 × 1 = 4mv, where E= Electromotive force, I = current, R = resistance.

35. If a toaster is connected to 440 V AC instead of 220 V AC, then the heat produced per second will be _______ of the initial amount. [RRC Group D 14/09/2022 (Afternoon)]

Correct Answer: (c) four times
Solution:

36. If a constant current of 2 A is maintained in a conductor of resistance 100Ω, then the potential difference across the conductor is: [RRC Group D 15/09/2022 (Afternoon)]

Correct Answer: (c) 200 V
Solution:

Given, Resistance (R) = 100 Ω, Current (I) = 2 A, V - potential difference.
By ohm’s law, V = IR,
so, V = 100 × 2 ⟹ V = 200 V.

37. The correct relation for heat produced by electric current is: [RRC Group D 15/09/2022 (Afternoon)]

Correct Answer: (b) H = V.I.T
Solution:

According to Joule's law of Heating, the heat energy generated is proportional to the time when the electric current and electrical resistance are constant.
We know that,
Energy = Power × Time
Heat Energy due to current = Electric
Power × Time
H= P × T
H = V × I × T {V= Potential Difference, I= Current} H = VIT
H = (I × R) × I × T (V= I R, Ohm's Law)
H = I²RT
H = VIT = V × v/R × T = V²/R T.
The unit of heat is joule.

38. Electric power consumed by two electric bulbs (each with 5 Ω resistance) connected in series with a 3 V battery is : [RRC Group D 15/09/2022 (Evening)]

Correct Answer: (c) 0.9 W
Solution:

V = 3V, R = 5 Ω Equivalent Resistance = R1 + R2 (In series) = 5 + 5 = 10 Ω
P = V²/R = 3 × 3/10 = 9/10 = 0.9 W

39. When 60 KJ heat is produced by a heater in 1 minute and 20 seconds then its power is : [RRC Group D 15/09/2022 (Evening)]

Correct Answer: (a) 750W
Solution:

Work = 60 KJ = 60 × 10⁻³ J
Time = 1 Minute and 20 Second = 60 + 20 = 80 Second
Power = work/time = 60 × 10³/80 =  750W

40. A bulb draws 36W when connected to a 12V supply. If it is connected to a 6V supply then power consumed will be [RRC Group D 16/09/2022 (Morning)]

Correct Answer: (c) 9W
Solution:

Given:- P = 36, V = 12