Utilization Of Electrical Energy : Practice Questions and Answers

Explanation: Sodium and Mercury Vapour Gas in Filament Lamps Definition: Sodium and mercury are two vapour gases commonly used in filament or discharge lamps due to their unique emission properties. These gases emit characteristic colors when excited by an electric current, making them suitable for various lighting applications. Sodium produces a yellow color, and mercury emits a green color when energized in such lamps.

Explanation: Factors Affecting Illumination Level in a Space Illumination refers to the amount of light falling on a surface and is an essential factor in creating an effective and comfortable environment for activities such as reading, working, or performing tasks. There are several factors that significantly affect the illumination level in a space, and understanding these factors is crucial for designing well-lit environments. Correct Option: The correct answer is: Option 2: The distance between the light source and the illuminated area.

Concept The total power consumed in the circuit is given by: P = V × I where, P = Power V = Voltage I = Current Calculation Given, Mains voltage = 230 V Lamps are 100 W each and behave as resistive loads (power factor ≈ 1) The circuit is protected by a 5 A fuse. For continuous loads, you should limit continuous current to 80% of the fuse rating (common safety practice/derating for continuous service) Allowed continuous current = 5 A × 0.8 = 4 A Current per lamp = ${100\space W\over 230\space V}=0.4348 \space A$ Number of lamps = ${4\space A\over 0.4348\space A}= 9$ So maximum = 9 lamps of 100 W each.

Explanation: Electric Traction Systems Definition: Electric traction refers to the use of electrical energy for driving locomotives, trams, trolleybuses, or other vehicles. It is a key technology in modern transportation systems, offering efficient and sustainable energy utilization compared to traditional methods like steam or diesel traction. Working Principle: Electric traction systems use electric motors powered by electricity, which can be sourced from overhead wires, third rails, batteries, or onboard power generation systems.

Concept: Since the primary limitation for the operation of an electric motor is its temperature rise, hence motor rating is calculated on the basis of its average temperature rise. The average temperature rise depends on the average heating which itself is proportional to the square of the current and the time for which the load persists. For example, if a motor carries a load L1 for time t1 and load L2 for time t2 and so on, then Average heating ∝ L12 t1 + L22 t2 +..........+ Ln2 tn, and the rating of the motor is given as ∴ size of the motor $= \sqrt {\frac{{L1^2\;{t1} + L2^2\;{t2} + \ldots + Ln^2\;{tn}}}{{{t1} + {t2} + \ldots + {tn}}}}$ Calculation: Let the full load L1 = 200 kW operated for time t1 = 10 min Half-full load L2 = L1 / 2 = 100 kW operated for time t2 = 20 min From above concept, ∴ Rating of the motor$= \sqrt {\frac{{{{200}^2} \times 10 + {{100}^2} \times 20}}{{10 + 20}}} =\sqrt{\frac{60\times 10^4}{30}}=100\sqrt {2}$ kW

Capacity of Battery: The capacity of a cell is the quantity of electricity that it can give out during a single discharge until its terminal voltage falls to discharging volts. It is measured by the product of current in amperes and the time in hours i.e. The capacity of cell = (I d × Td) ampere-hours (or Ah) Id = Steady discharging current in amperes & Td = Time in hours for which the cell can supply current until its voltage falls to discharging volts For lead-acid cell is taken up to a point till it discharges down to 1.8 volts Application: We have, Id = 2 A Td = 15 hours Hence, The capacity of cell = (Id × Td) = 2 × 15 = 30 Ah