General Knowledge

Ethiopia is often referred to as the "Roof of Africa" due to its extensive high central plateau, which covers a significant portion of the country. Much of Ethiopia's land area, including its capital city Addis Ababa, lies at an elevation of over 1,000 meters above sea level. The average elevation of the country is approximately 1,300 meters, making it one of the highest countries in Africa and globally in terms of average altitude.

Tungsten (W) possesses the highest melting point of all known metals, approximately 3,422 °C (6,192 °F or 3,695 K). Only carbon, in its various allotropic forms (like graphite or diamond), has a higher sublimation point (carbon does not melt at standard pressures but sublimes).

This exceptional property makes tungsten indispensable in numerous high-temperature applications. It is widely used for filaments in incandescent light bulbs, electrodes, X-ray targets, and heating elements in high-temperature furnaces. Its high density, hardness, and significant strength at elevated temperatures further contribute to its utility in various industrial and military applications.

যমুনা নদী বাংলাদেশের অন্যতম প্রধান নদী এবং দৈর্ঘ্যের দিক থেকে এটিকে বাংলাদেশের দীর্ঘতম নদী হিসেবে বিবেচনা করা হয়। এটি ব্রহ্মপুত্র নদের প্রধান শাখা, যা ভারতে ব্রহ্মপুত্র নদ নামে পরিচিত এবং বাংলাদেশে প্রবেশ করার পর যমুনা নাম ধারণ করে। যমুনা নদী একটি প্রশস্ত ও বিনুনিযুক্ত নদী, যা দক্ষিণ দিকে প্রবাহিত হয়ে আরিচার কাছে পদ্মা নদীর (গঙ্গা নদীর প্রধান শাখা) সাথে মিলিত হয়েছে। এরপর মিলিত স্রোত মেঘনা নামে পরিচিত হয়ে বঙ্গোপসাগরে পতিত হয়েছে। বাংলাদেশের ভৌগোলিক সীমানার মধ্যে এর দীর্ঘ প্রবাহের কারণে যমুনা নদীকেই সাধারণত দেশের দীর্ঘতম নদী হিসেবে ধরা হয়।

Challenger Deep, Mariana Trench

The deepest known point in the Earth's oceans is the Challenger Deep, located in the western Pacific Ocean at the southern end of the Mariana Trench. Its deepest measurement is approximately 10,984 meters (36,037 feet), though estimates vary slightly. This depth is nearly 7 miles, making it significantly deeper than Mount Everest is tall. The Mariana Trench itself is a crescent-shaped scar in the Earth's crust, formed by the subduction of the Pacific Plate under the Mariana Plate, where one tectonic plate slides beneath another.

Electrical conductance is a measure of how easily electricity flows through a material. It is the reciprocal of electrical resistance, meaning that a material with high conductance has low resistance, and vice versa. The SI unit for electrical conductance is the siemens (symbol: S), named after the German inventor and industrialist Ernst Werner von Siemens. In older terminology, it was also referred to as the mho (ohm spelled backward).

Mathematically, conductance (G) is given by the formula \(G = \frac{1}{R}\), where R is the electrical resistance in ohms. According to Ohm's law, \(I = G \times V\), where I is the current and V is the voltage. Conductance plays a crucial role in the analysis of electrical circuits, especially in parallel circuits where individual conductances add up.