Conceptual Physics

What is Half Value Layer

Half Value Layer indicates the thickness of absorbing material which is needed to reduce the incident radiation intensity by a factor of two.

Half Value Layer for different materials is provided in the below table

INCONEL® (nickel-chromium-iron) alloy 600 (UNS N06600/W.Nr. 2.4816) is a standard engineering material for applications which require resistance to corrosion and heat. The alloy also has excellent mechanical properties and presents the desirable combination of high strength and good workability. The limiting chemical composition of INCONEL alloy 600 is shown in Table 1. The high nickel content gives the alloy resistance to corrosion by many organic and inorganic compounds and also makes it virtually immune to chloride-ion stress-corrosion cracking. Chromium confers resistance to sulfur compounds and also provides resistance to oxidizing conditions at high temperatures or in corrosive solutions. The alloy is not precipitation hardenable; it is hardened and
strengthened only by cold work. The versatility of INCONEL alloy 600 has led to its use in a variety of applications involving temperatures from cryogenic to above 2000°F (1095°C). The alloy is used extensively in the chemical industry for its strength and corrosion resistance. Applications include heaters, stills, bubble towers and condensers for processing of fatty acids; evaporator tubes, tube sheets and flaking trays for the manufacture of sodium sulfide; and equipment for handling abietic acid in the manufacture of paper pulp. The alloy's strength and oxidation resistance at high temperatures make it useful for many applications in the heat-treating industry. It is used for retorts, muffles, roller hearths and other furnace components and for heat-treating baskets and trays. In the aeronautical field, INCONEL alloy 600 is used for a variety of engine and airframe components which must withstand high temperatures. Examples are lockwire, exhaust liners and turbine seals. INCONEL alloy 600 is used in the electronic field for such parts as cathode-ray tube spiders, thyratron grids, tube support members and springs.The alloy is a standard material of construction for nuclear reactors. It has excellent resistance to corrosion by high-purity water, and no indication of chloride-ion stress-corrosion cracking in reactor water systems has been detected. For nuclear applications, the alloy is produced to exacting specifications and is designated INCONEL alloy 600T.

Courtesy: M/s Special Metals

How long does it take for moonlight to reach the earth?

Light travels through space at just over 186,000 miles per second. The moon is just under 250,000 miles from Earth, so light from the Moon's surface has to travel more than one second (about 1.3 seconds) to reach us.

The astronauts left reflecting mirrors on the moon. By shining a laser beam on those mirrors from Earth, and measuring the time (less than 3 seconds) it takes to see its reflection, the length of the round trip can be easily calculated to within a few inches!

Which planet rotates so fast that its day is only 10 hours long?

Both Jupiter and Saturn have days that last about 10 hours. Jupiter has a period of 0.410 earth days or about 9.84 hours and Saturn has a period of 0.426 earth days or about 10.224 hours.

What is the Astronomical Unit?

When describing distances on the scale of our Solar System, conventional units of measure are not conveniently sized. Miles are too small, and light years are too large, to permit easily compared numbers. For example, the distance between the Sun and Earth is about 93,000,000 miles; between the Sun and Pluto is about 3,700,000,000 miles. Comparing those two numbers, it is not easily seen that Pluto is about 40 times as far from the Sun as Earth is.

The Astronomical Unit (AU) represents a distance of Earth's average distance to the Sun, or about 93,000,000 miles.

How did planet Neptune get its name?

In Roman mythology Neptune was the god of the Sea.

After the discovery of Uranus, it was noticed that its orbit was not as it should be in accordance with Newton's laws. It was therefore predicted that another more distant planet must be perturbing Uranus' orbit. Neptune was first observed by Galle and d'Arrest on 1846 Sept 23 very near to the locations independently predicted by Adams and Le Verrier from calculations based on the observed positions of Jupiter, Saturn and Uranus. An international dispute arose between the English and French (though not, apparently between Adams and Le Verrier personally) over priority and the right to name the new planet; they are now jointly credited with Neptune's discovery. Subsequent observations have shown that the orbits calculated by Adams and Le Verrier diverge from Neptune's actual orbit fairly quickly. Had the search for the planet taken place a few years earlier or later it would not have been found anywhere near the predicted location.

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What is the hottest part of Sun?

The center of the sun is the hottest part (at around 15 million Kelvins, or 27 million degrees Fahrenheit). The temperature then drops to 5,800 K (10,000 degrees F) at the visible surface, although the corona (the part just above the surface, where solar flares are), can get much hotter (2 million K, or 3.6 million degrees F).

What is the difference between cathode rays and beta rays?

cathode 'rays' were observed in electrical experiments because of their fluorescent effect near a negatively charged plate (called the cathode) in a vacuum. They were only later found to be negatively charged electrons emitted from negatively charged plates and accelerating toward positively charged ones. (Like charges repel, unlike charges attract.)

Beta 'rays' were first observed being emitted from certain unstable (radioactive) isotopes, and behaved unlike the alpha and gamma radiation also found in radioactivity. It wasn't until later that both alpha and beta 'radiation' were discovered to actually be particles; only gamma rays consist of true electromagnetic radiation. Beta 'rays' are actually electrons ejected from decaying neutrons, and are now more often referred to as Beta emission or Beta particles.

So electrons can be described differently, not based on WHAT they are but HOW they are created or observed.

How fast do electrons travel when moving as an electrical current through copper wire?

The actual velocity of electrons through a conductor is measured as an average speed called drift velocity. This is because individual electrons do not traverse straight line paths in conductors, instead they move in a random zig-zag motion, changing directions as they collide with atoms in the conductor. Thus, the actual speed of the electrons through the conductor is very small in the direction of current.

For example, the drift speed through a copper wire of cross-sectional area 3.00 x 10^-6 m², with a current of 10 A will be approximately 2.5 x 10^-4m/s or about a quarter of a milimeter per second.

What is Plasma?

A plasma (or, more properly, an electromagnetic plasma) is a phase of matter that has enough energy for the electrons to separated from the nucleus. It consists of independently moving electrons and nuclei, and thus has some rather interesting properties, such as very good magnetic shielding. It can be found in places such as the center of the sun, and also, in small quantities, surrounding a lightening bolt.

Many people consider solid, liquid, gas and plasma to be the only four phases of matter. This is not true, as there exist many others, but they are generally more exotic with names like hadron gas or Bose-Einstein Condensate.