QUES: While inert gas reduces filament evaporation, it also conducts heat from the filament, thereby cooling the filament and reducing efficiency. At constant pressure and temperature, the thermal conductivity of a gas depends upon the molecular weight of the gas and the cross sectional area of the gas molecules. Higher molecular weight gasses have lower thermal conductivity, because both the molecular weight is higher and also the cross sectional area is higher. Xenon gas improves efficiency because of its high molecular weight, but is also more expensive, so its use is limited to smaller lamps.

Why does inert gas reduce efficiency?
What is the answer?
ANS: conducts heat from the filament, thereby cooling the filament
QUES: At its greatest extent, the Achaemenid Empire included the modern territories of Iran, Azerbaijan, Armenia, Georgia, Turkey, much of the Black Sea coastal regions, northeastern Greece and southern Bulgaria (Thrace), northern Greece and Macedonia (Paeonia and Ancient Macedon), Iraq, Syria, Lebanon, Jordan, Israel, Palestine, all significant ancient population centers of ancient Egypt as far west as Libya, Kuwait, northern Saudi Arabia, parts of the UAE and Oman, Pakistan, Afghanistan, and much of Central Asia, making it the first world government and the largest empire the world had yet seen.

The Achaemenid Empire controlled all of the significant settlements of what ancient country during its greatest extent?
What is the answer?
ANS: ancient Egypt
QUES: Avicenna's astronomical writings had some influence on later writers, although in general his work could be considered less developed than Alhazen or Al-Biruni. One important feature of his writing is that he considers mathematical astronomy as a separate discipline to astrology. He criticized Aristotle's view of the stars receiving their light from the Sun, stating that the stars are self-luminous, and believed that the planets are also self-luminous. He claimed to have observed Venus as a spot on the Sun. This is possible, as there was a transit on May 24, 1032, but Avicenna did not give the date of his observation, and modern scholars have questioned whether he could have observed the transit from his location at that time; he may have mistaken a sunspot for Venus. He used his transit observation to help establish that Venus was, at least sometimes, below the Sun in Ptolemaic cosmology, i.e. the sphere of Venus comes before the sphere of the Sun when moving out from the Earth in the prevailing geocentric model.

What subject did Avicenna consider to be a separate discipline from astronomy?
What is the answer?
ANS:
unanswerable