General Science


PHYSICS: ELECTRICITY

Overview
  • Electricity is an extraordinarily versatile source of energy
  • Electricity is the backbone of modern industrial society
  • The phenomenon of electricity includes concepts such as 
    • Electric charge: a property of subatomic particles that determines their electromagnetic interactions
    • Electric current: a movement or flow of charged particles
    • Electric field: influence of charged particles on other charged particles in the vicinity
    • Electric potential: capacity of an electric field to do work
    • Electromagnetism: interaction between electric and magnetic fields
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TIMELINE OF EARLY DISCOVERIES/INVENTIONS

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BASIC ELECTRICAL COMPONENTS
  1. Resistors
    1. Resistors are materials that resist the flow of current through them
    2. They dissipate energy in the form of heat
    3. Ohmic materials are those materials whose resistance remains constant over a range of temperatures and currents. Non-ohmic materials have resistances that change
    4. The unit of resistance is Ohm
  2. Capacitors
    1. Capacitors are devices that store electric energy in the form of electric charge
    2. They usually consist of two conducting plates separated by a thin insulating layer
    3. Capacitors block steady state current i.e. DC current
    4. The unit of capacitance is Farad
  3. Inductors
    1. Inductors are conductors that store energy in a magnetic field, which is produced in response to an electrical current
    2. Inductors allow steady current, but oppose rapidly changing currents
    3. The unit of inductance is Henry
  4. Transformers
    1. A transformer is a device that transfers electrical energy from one circuit into another
    2. This transfer occurs through inductively coupled conductors, where varying current in one circuit creates a varying magnetic field (and hence voltage) in the other circuit
    3. Transformers can be used to step-up or step-down voltages from high voltage transmission lines to appliances in homes
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ELECTRICITY IN NATURE
  1. Electric shock
    1. A voltage applied to the human body causes an electric current through the tissues
    2. In general, greater the voltage applied, greater the current passed through the tissues
    3. Voltages 100-250 V can be lethal in humans, although as low 32V has been lethal sometimes. Lethality increases dramatically beyond 250V
    4. If the current is sufficiently high, it can cause muscle contractions, fibrillation of the heart and tissue burns
    5. DC tends to cause continuous muscle contractions making the victim hold on to a live conductor, thereby increasing risk of tissue burn
    6. AC tends to interfere with heart function, increasing risk of cardiac arrest
    7. AC at high frequencies, causes current to travel on the surface due to skin effect. This results in severe burn but is usually not fatal
  2. Electrical phenomena
    1. Touch, friction and chemical bonding are all due to interactions between electrical fields on the atomic scale
    2. The Earth’s magnetic arises from a natural dynamo of circulating currents in the planet’s core
    3. Piezoelectric crystals like quartz and sugar generate electric current when subject to mechanical pressure
    4. Electric eels detect and stun their prey via high voltages (500 V) generated from muscle cells called electrocytes
    5. Electrical currents, called Action Potential, are used for nervous system communication in all animals, including humans

CHEMISTRY: EXPLOSIVES

Overview
  • An explosive is a substance that contains a great deal of stored energy that can produce an explosion, usually accompanied by the production of light, heat and pressure
  • The energy stored in an explosive material may be
    • Chemical energy such as nitroglycerine
    • Pressurised compressed gas such as a gas cylinder or aerosol can
    • Nuclear energy such as Uranium and plutonium
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CHEMICAL REACTIONS IN EXPLOSIVES
  1. Deflagration
    1. Deflagration is a term that describes subsonic combustion that propagates through thermal conductivity
    2. Deflagration is easier to control and so is used when the goal is to move an object with the force of expanding gas
    3. Examples of deflagration include gas stove, internal combustion engine, gunpowder, pyrotechnics etc
  2. Detonation
    1. Detonation is a combustion process in which a supersonic shock wave through the body of a material
    2. In detonation, a supersonic shock wave originating at the point of ignition compresses the surrounding material, thus increasing its temperature to the point of ignition
    3. Because detonations generate high pressures, they are much more destructive than deflagrations
    4. Detonations are difficult to control and are used primarily for demolition and in warfare.
    5. Examples of detonation includes high explosives, oxygen-methane mixture
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CLASSIFICATION OF EXPLOSIVES
  1. High explosives
  • Materials that explode faster than the speed of sound are called high explosives
  • This type of explosion is known as detonation
  • Used in mining, demolition and military applications
  1. Low explosives
    1. Materials that explode slower than the speed of sound are called low explosives.
    2. This type of explosion is known as deflagration
    3. Used as propellants, gun powder, pyrotechnics (such as flares and fireworks)
  2. Primary explosives
    1. A primary explosive is an explosive that is extremely sensitive to stimuli. These stimuli include impact, friction, heat, static electricity and electromagnetic radiation
    2. For primary explosives, a relatively small amount of energy is required for initiation of explosion
    3. In general, primary explosives are considered to be those explosives that are more sensitive than PETN
    4. Used in detonators to trigger larger charges of more stable secondary explosives
    5. E.g.: Mercury fulminate, Nitrogen trichloride, acetone peroxide, ammonium permanganate
  3. Secondary explosives
    1. Secondary explosives are less sensitive than primary explosives and require more energy to be initiated
    2. They are safer to handle and store
    3. In general, secondary explosives are considered to be those explosives that are less sensitive than PETN
    4. Secondary explosives are usually used in large quantities and are initiated by small amounts of primary explosives
    5. E.g.: TNT, RDX
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SOME COMMON EXPLOSIVES
  1. Trinitrotoluene (TNT)
    1. TNT is a useful explosive material with convenient handling properties. TNT is sometimes also used as a reagent in chemical synthesis
    2. TNT was first prepared by Joseph Wilbrand (GermanY) in 1863
    3. The explosive yield of TNT is considered to be the standard measure of strength of bombs and other explosives
    4. Sulphitation is a process used in the manufacture of TNT, specifically to stabilize the explosive
    5. TNT is one of the most commonly used explosives for industrial and military applications
    6. It is insensitive to shock and friction, reducing the occurrence of accidental detonation. TNT melts without exploding (allowing it to be combined with other explosives), does not absorb or dissolve in water (allowing use in wet environments) and is stable compared to other explosive
    7. TNT contains energy of 4.6 Mega Joules per kilogram (MJ/kg). By comparison gun powder contains 3 MJ/kg, dynamite contains 7.5 MJ/kg and gasoline contains 47.2 MJ/kg
    8. TNT is used as a reference for other explosives. Nuclear weapons have energy content measured in kilotonnes (kT) or megatonnes (MT) of TNT equivalent. 
    9. TNT is usually used in mixture with other substances. E.g.: Amatol (TNT + ammonium nitrate)
  2. RDX
    1. RDX, chemically cyclotrimethylnetrinitramine, is also known as cyclonite and T4
    2. RDX is usually used in mixture with other explosives and plasticizers
    3. RDX is stable in storage and is considered one of the most powerful of military explosives
    4. RDX was discovered in 1898 by Goerg Friedrich Henning (Germany)
  3. Pentaerythritol tetranitrate (PETN)
    1. PETN is one of the most powerful high explosives known
    2. It is more difficult to detonate than primary explosives, but less stable than secondary explosives
    3. It is more sensitive than other high explosives, and is rarely used alone
    4. Usually used in small calibre ammunition, detonators of land mines
    5. PETN is an effective underwater explosive
    6. PETN is a major ingredient of Semtex (plastic explosive)
    7. PETN was first synthesised by Bernhard Tollens (Germany) in 1891
  4. Dynamite
    1. Dynamite is based on nitroglycerine
    2. It was invented by Alfred Nobel (Sweden) in 1867
    3. Used mainly for mining, quarrying, construction
    4. Dynamite was the first safely manageable explosive stronger than black powder
  5. Plastic explosive
    1. Plastic explosives are explosives that are soft and can be moulded by hand
    2. Common plastic explosives include Semtex (Czech Republic) and C-4 (USA)
    3. Used mainly for demolition, also used by terrorists
    4. The first plastic explosive was Gelignite, invented by Alfred Nobel (Sweden) in 1875
    5. C-4 (composition 4) is made of RDX while Semtex is made from RDX and PETN
    6. Semtex became notoriously popular with terrorists because it is difficult to detect. Semtex was invented by Stanislav Berbera (Czech R.) in the 1950s
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BIOLOGY: CLONING

Overview
  • Cloning is the process by which genetically identical individuals are produced
  • Cloning happens in nature by the biological mechanisms of asexual reproduction in bacteria, insects and plants
  • Cloning can also be performed artificially by copying fragments of DNA (molecular cloning) or cells (cell cloning) or organisms
  • Mammals, which reproduce sexually, cannot clone naturally. Mammals inherit genetic material half each from both parents, meaning that the progeny is never an identical replica of the parent. Natural clones in mammals are confined to the production of identical twins
  • The first vertebrate to be cloned was a tadpole by Robert Briggs (USA) and Thomas King (USA) in 1952
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Cloning in plants
  • Plants have been clone for a long time. 
  • Grafting is a form of plant cloning
  • Many horticulture plants are cloned, having been derived from a single individual
  • Examples of plant cloning include carrots, tobacco, potato, banana
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Cloning in animals
  • Cloning of animals is based on a technique known as “somatic cell nuclear transfer”.
  • Nuclear transfer involves fusing two cells together – a donor cell containing all its DNA, and egg cell with all its DNA removed
  • The two cells are fused with an electric pulse and the resulting enucleated egg is implanted in the mother
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Dolly the Sheep
  • Dolly, a Finn Dorset ewe, was the first mammal to be successfully cloned from an adult cell
  • Dolly was cloned by Ian Wilmut and Keith Campbell at the Roslin Institute in Edinburgh (Scotland)
  • Dolly was born in 1996 and lived for six years
  • The donor cell for Dolly was taken from a mammary gland.
  • Production of a healthy clone proved that a cell from a specific part of the body could recreate a whole individual
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Some animals that have been cloned
Cloned animalWhenWhereBy whomNotes
Tadpole1952USARobert Briggs, Thomas King
Carp (fish)1963ChinaTong Dizhou
Mice
(first cloned mammal)
1986Soviet UnionChaylakhyan, Veprencev, Sviridova, NikitinFirst cloned mammal
Sheep
(first cloned mammal from adult cell)
1996BritainIan WIlmut, Keith CampbellFirst cloned mammal from adult cell
Rhesus monkey
(named Tetra)
2000It was named Tetra
Gaur (Asian Ox)2001USAJonathan Hill, Philip DamianiNamed Noah
First endangered species to be cloned
Cat2001 (Copycat)
2004 (Little Nicky)
USACopycat was the first cloned pet
Little Nicky was the commercially produced cat clone
Mule (named Idaho Gem)2003USAGordon Woods, Dirk VanderwallFirst clone in horse family
Horse (named Prometea)2003ItalyCesare GalliFirst cloned horse
First animal to be born from and carried by its cloning mother
Water buffalo
(called Samrupa)
2009IndiaS K Singla and others at Karnal National Dairy Research InstituteFirst cloned buffalo
Died 5 days after birth due to lung infection
Camel
(called Injaz)
2009DubaiNisar Ahmad WaniFirst cloned camel
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