Why does an MCB sometimes switch off immediately after being turned on?

Kathmandu – In this week's edition (Kartik 23) of the "Energy Knowledge" column, published every Friday by Urja Khabar, we have attempted to provide information on various aspects of electricity flow. Last week, we discussed the advantages and disadvantages of diesel electric power plants.

1. What is the difference between the voltage in a household circuit and the voltage in a car battery?

Answer: The voltage available in homes is known as AC (Alternating Current) voltage, whereas the voltage from a car battery is known as DC (Direct Current) voltage. Household voltage is 230 volts, while the voltage required for a car is typically 12 volts. Some vehicles require 24 volts, which can be achieved using two 12-12 volt batteries.

2. Why do the lights in a house suddenly dim?

Answer: The reasons for this could be:
(a) A fuse in one of the dropout sets of the transformer has blown. If one fuse blows, the lights on two phases will dim, while the lights on the third phase will remain as bright as usual.
(b) There might be a loose connection in the service cable running from the meter to the pole.
(c) A jumper from one of the three phases of the 11 kV line might be loose or broken.
The most likely causes are (a) or (c).

3. What happens to an airplane when lightning strikes it?

Answer: Planes sometimes pass through lightning flashes, but passengers remain unharmed. The plane might experience minor damage at the points where the lightning enters and exits. Lightning is the flow of electrons, similar to how water flows. The outer part of the plane is made of conductive metal, which channels the electrons safely outside. This phenomenon can be compared to a Faraday cage, where the electrical charge stays on the outer surface, protecting anything inside. Even though lightning strikes the cage, the people inside remain safe.

Multiple-Choice Questions:

How is current calculated?
(a) By dividing voltage by resistance (Ohms)
(b) By dividing resistance (Ohms) by voltage
(c) By dividing watts by voltage
(d) By dividing watt-hours by voltage
Answer: (a) By dividing voltage by resistance (Ohms)

What is the unit for inductance?
(a) Ohm
(b) Henry
(c) Tesla
(d) Watt
Answer: (b) Henry

What happens when the power factor of a load decreases?
(a) Voltage increases
(b) Current increases
(c) Resistance decreases
(d) Nothing happens
Answer: (b) Current increases

What is the unit of electrical energy?
(a) Watt-hour
(b) Watt
(c) Volt
(d) Ampere
Answer: (a) Watt-hour

Which device is used to increase the power factor in industries?
(a) Inductor
(b) Capacitor
(c) Resistor
(d) Current transformer
Answer: (b) Capacitor

What is the minimum current (in milliamps) that can cause death in a person?
(a) 1
(b) 5
(c) 50
(d) 100
Answer: (c) 50