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Index (B)

BA - BC

BD - BF

BG - BJ

BK - BN

BO - BO

BP - BR

BS - BV

BW - BZ

Moment of truth
The Sun, with a diameter of 1,392,000 km, is made of 94% hydrogen atoms.


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brass Eng.
A group of alloy consisting of copper and zinc. For instance yellow brass, a common form of brass, consists of 67% copper and 33% zinc. Brass is golden yellow. Although it is more resistant to weathering than copper, it can still easily tarnish and is usually coated with a clear lacquer. Brass is ductile and used to make castings, scientific and music instruments and other industrial uses.

breakdown voltage Phys.
The potential difference at which an insulating substance undergoes a physical or chemical change that causes it to become a conductor, thus allowing current to flow through the sample.

brine Chem.
An aqueous solution of sodium chloride (table salts), often contains other salts such as magnesium chloride. Natural occurring brine can be obtained by pumping water into underground salt mine. Seawater is also a brine that contains, on average, 3.3 g of sodium chloride in every 100g of seawater. It is used as a preservative in food industry and in refrigeration and cooling systems.

Britannia metal Eng.
An alloy consisting of 80-90% tin, 5-15% antimony and sometimes with a small amount of bismuth, lead, copper and zinc. It has a similar appearance of pewter, which is brilliant silvery white, but Britannia metal is harder. It is use to make bearings, cooking utensil and decorative domestic articles such as drinking vessels and other table wares.

Bronsted-Lowry theory Chem.
A theory of acids and bases proposed independently by Johannes Bronsted and Thomas Lowry in 1923, which states that an acid is a substance that donates protons and a base is a substance that accepts protons. For example, when hydrogen chloride is dissolved in water, it dissociates into protons (H+) and chloride ions (Cl-). The protons interact (donate) with water molecules to give the oxonium ion (H3O+).

bronze Eng.
A group of copper alloys, mainly with tin. The amount of tin can vary from as little as 1% to 30% and sometimes with lead and zinc. The alloys are usually harder and more durable than iron. It is easily cast and extensively used in bearings, valves and other machinery parts. There are many other sub-classes of bronze that does not contain tin. For instance, aluminium bronze that alloys with aluminium. Bronze has been used since prehistoric era around 3300 BC (Bronze Age) for making tools, weapons and armor.

brown dwarf Astron.
Clouds of gas and dust that collapse under gravity to form a star. However, there is not enough mass to initiate core nuclear fusion (a process that cause stars, and our Sun, shine and give out heat). As a result, these 'failed stars' form compact, dark (not necessary brown!) objects. Brown dwarfs are usually small, comparatively cold (probably less then 1000C). For this reason, these celestial objects are not bright, and very difficult to detect. The absolute brightness is estimated to have a magnitude of about +17. The first brown dwarf was observed (Gliese-229B) in 27 October 1994 using the 60 inch reflecting telescope on Palomer Mountain in infrared light.

Brownian motion Phys.
The random movements of small particles, suspended in a fluid, which arise from collisions with the fluid molecules. It was discovered by Robert Brown, a biologist, in 1827. The theoretical analysis was first carried out by Louis Bachelier (1870-1946) in 1900 but greatly advanced by Einstein in 1905.

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