Sunday 11 March 2012

The coffee ecosphere consists of all living things, all inorganic materials and physical forces interacting with one another. Understanding the coffee ecosphere aids in unraveling the energy flows, deciphering the interactions between living things and the environment, the transfer of food, the flow of energy and the exchange of inorganic nutrients and organic compounds. The coffee grid in turn depends upon the delicate balance of ecological processes for the fulfillment of its needs. The coffee ecosystem closely interacts with the BIOTIC (LIVING) & the ABIOTIC (NON-LIVING) environment. The relationships between the different factors are so smooth and often so subtle that seldom we are aware of the immense structural and functional complexities involved. Within the coffee mountain there is a great diversity in the types of ecosystems because of the change in elevation within a single zone. The energy balance within each system, ultimately determines the health of the coffee forest. The dominant energy which enters the coffee ecosystem is mainly in the form of sunlight and is used by photosynthetic organisms in the synthesis of organic matter. The energy and the nutrients obtained from the nutrient pool of the soil move from producers to herbivores. A part of this energy is dissipated by the organisms during respiration and the rest made available to herbivores, which are animals that consume the photosynthesizers. The herbivores in turn make use of this energy in the build up of cellular constituents and make way for the carnivores. The carnivores use the herbivores as their primary energy source and the food chain continues with one carnivore eating the other. It is of paramount importance to remember that every step is characterized by a chain of events leading to energy loss in the form of heat. Death or destruction of flora or fauna results in the establishment of DECOMPOSERS. The decomposers act on the litter, decaying plants and animals and return the minerals to the nutrient pool. The primary decomposers are the microorganisms. Microorganisms utilize energy released by plants and animals in the form of excretory products.

BIOTIC COMPONENTS: Producers, Consumers, Decomposers

ABIOTIC COMPONENTS: ENVIRONMENT, INORGANIC ELEMENTS, CARBON, OXYGEN, HYDROGEN, WATER, POSPHATES, CARBONATES Minerals, Liquids, Gases, PHYSICAL FACTORS-MOISTURE, AIR CURRENTS, LIGHT.ETC. ORGANIC: Proteins, Carbohydrates, lipids, etc.

MACROCONSUMERS OR PHAGOTROPHS: Heterotrophic organisms mainly animals. Organisms which obtain their energy from sources other than themselves, indirectly or directly.MICROCONSUMERS: Chiefly Bacteria, fungi. Actinomycetes.They break complex organic molecules into simpler compounds for producers.

PRODUCERS OR AUTOTROPHS: These are the green plants with the help of chlorophyll prepare their own food. Since, green plants or producers convert solar energy into chemical energy, they are sometimes referred to as transducers of energy.

CONSUMERS

The physical and chemical environment inside the coffee mountain plays an important role in the distribution of energy levels. Within the boundaries of the coffee mountain biotic partners interact and carry out their activities significantly modifying the characteristics of the mountain. Only a small fraction of the solar energy (< 10 % of the total solar energy falling upon the coffee forest is used by the first tropic level. This chemical energy stored in the plant tissues is used up by the plant to carry out its physiological activities and a part of the energy is transferred to the next tropic level, namely consumers, also referred to as HETEROTROPHS. Along the transformation path, there is a loss of certain amount of energy. Further, the flow of energy is always unidirectional and gradually tapers. Useful energy level steadily declines from one tropic level to the other.

ECOLOGICAL PYRAMID

An inside view of the coffee mountain reveals a highly organized and intelligent ecological pyramid. First come the producers (Tall evergreen trees, herbs, shrubs, climbers,) and then a regular decrease in the energy, biomass and number of organisms occupying a tropic level. The pyramid starts with a broad base and ends tapering at the apex.

PYRAMID OF NUMBERS: It indicates the numerical relationship between the different tropic levels of the food chain.
PYRAMID OF ENERGY: Explains the movement of energy flow at each tropic level as well as the role played by different organisms in the transfer of energy. Energy pyramids are always slopping. Greater amount of energy is available at the producer level and gradually decreases by the time it reaches the primary consumer level. In turn Energy production of the primary consumers is greater than that of the secondary consumers.
PYRAMID OF BIOMASS: Represents the total dry matter present in the ecosystem at any one given point of time.

The energy sources within the coffee mountain are highly variable depending on the seasons. Some nutrients are available only for short periods of time because of the rapid colonization and consumption of microorganisms and in some cases depending on the leaf shedding there is an excess of nutrients on the floor of the forest. The best part of the energy equation is that microorganisms have evolved highly sophisticated regulatory mechanisms to make use of the available energy resources. This has a tremendous bearing on the quantitative yield and qualitative yield of coffee.

Depending on the elevation, rainfall, temperature and other related physical factors the coffee mountain is organized into a large number of intersecting food WEBS. This complex food web consists of diverse number of species, the populations of which have reached equilibrium in terms of rate of multiplication and destruction. Any sudden or drastic change in equilibrium results in the break down of the natural rhythm of the ecosystems.

JOE'S SUSTAINABLE FORMULA: THE KIREHULLY EXPERIMENT

Based on our very own experiments as well as collecting data from fellow farmers we have arrived at a few significant conclusions which will help coffee farmer's world wide in maintaining the productivity and a sound ecological balance within their coffee farm.

Productivity is generally defined in terms of the amount of dry matter accumulated within a specified period, expressed in grams/m?/day. The productivity of green plants is known as primary productivity and that of consumers and decomposers as secondary productivity.

GROSS PRODUCTIVITY: It is a reflection of the sum total of organic compounds accumulated, inclusive of the amount used in respiration by the plants during which measurements are made.

NET PRODUCTIVITY: Refers to the amount of organic compounds stored by the plants in their tissues.

For every ton of raw coffee (Arabica) sold, the coffee farmer needs to externally add up to two tons of compost. In case of Robusta coffee, the required compost is one and a half tons.
For every ton of anticipated coffee, two and a half tons of compost should be added in the available form.
The raw materials used for compost should have a low carbon nitrogen ratio and it is preferable to use Sheep, poultry and cattle manure mixed along with raw neem seeds, coffee pulp and green leaves of erythrina indica and glyrecedia immaculate.
Timing of application of compost is very important. Check other articles (Fine art of composting, organic manures).
It is not advisable to only use cattle manure as a base for compost. Every compost pit should be lined with soil from fertile cradle pits or water trenches to boost the native micro flora.
In case of ROBUSTA, with increase in age of plants, the application of nitrogenous fertilizers should be reduced.

HOMEOSTASIS: AND CYBERNETICS

HOMEO=SAME, STASIS=STANDING. To a considerable extent, coffee ecosystems are self regulating entities that have a high degree of equilibrium or homeostasis. The environment and the organisms are both products of a continuous process of change. Cybernetics refers to undesirable man made changes in trying to disturb the natural controls. For e.g. In spite of dramatic changes in the weather due to depleting forest cover or sudden rise in hydrogen ion concentration, due to excessive application of nitrate fertilizers, the coffee bush as well as the surrounding flora and fauna try to adjust their physiological activity by switching on and switching off a few essential genetic components so as to not be affected by the sudden change. However, if the changes persist over an extended period of time, then there is every likelihood in the collapse of the biotic system.

CONCLUSION

Evolutionary biologists have time and again arrived at one scientific truth that has great relevance for shade grown Indian coffee plantations. They are of the opinion that it is not necessarily the strongest or the largest species that survive, but the one's most responsive to change. However, it is to be observed that these changes should be gradual and a product of nature rather than man made, sudden and dramatic. When the changes are slow, it gives adequate time and ability for the biotic partners to adapt and transform to survive the changing times and thrive. Nature is an amazing survivor under such circumstances.

Managing coffee plantations has been a deeply enriching experience for the two of us. Our observations for the past 20 years point out that the coffee forests possess the most luxuriant vegetation of all biomes and there is a strong ASSOCIATIVE INFLUENCE among various biotic components inside the coffee mountain. The coffee ecosystem is mutually inter connected and interrelated. A few factors like global warming, geo chemical changes, destruction of forests, commercial logging, toxic levels of pesticide residues can drastically imbalance or upset the food supply chain resulting in the break down of food webs. The reason may be attributed to the fact that we have not been able to understand the delicate and orderly balance that exists in the natural ecosystems. One has to bear in mind that all food chains are cyclic in nature.

Tim Radford reports in the "GUARDIAN" under the title BLUE PLANET'S RED BALANCE SHEET that the human race is living beyond its means. A report backed by 1360 scientists from 95 countries-some of them world leaders in their fields warns that almost two thirds of the natural machinery that supports life on earth is being degraded by human pressure. The wetlands, forests, savannahs, estuaries, coastal fisheries and other habitats that recycle air, water and nutrients for all living creatures are being irretrievably damaged. In effect, one species is now a hazard to the other 10 million or so on the planet, and to itself. Human activity is putting such a strain on the natural functions of earth that the ability of the planet's ecosystems to sustain future generations can no longer be taken for granted. The report prepared in Washington under the supervision of a board chaired by Robert Watson, the British born chief scientist at the world bank and a former scientific adviser to the White house, will be launched soon at the Royal Society in London. It warns that because of human demand for food, fresh water, timber, fiber and fuel, more land has been claimed for agriculture in the last 60 years than in the 18th and 19th centuries combined. An estimated 24% of the earth's land surface is now cultivated.

One burning question that remains in our mind is that at the present rate of destruction whether coffee mountains will remain without biodiversity? Coffee farmer's world wide should be cautious in destroying forest relationships.

In the new world order, the temptation of using chemicals and pesticides is even greater. This practice can contaminate food webs. At each level of the food chain, chemicals and heavy metals can go on concentrating and finally get embedded in the human body as a result of BIOMAGNIFICATION. This can result in dire consequences for future generations. The ultimate aim of technology should be in preserving nature.

Everything that man has made in this world is surpassed by nature. We need to focus on the small details in order to better appreciate the larger spectrum. This will enable us to be conscience to the many dimensions of our existence and treat the resources of the mountain with respect. A sustainable system empowers coffee farmers to build better lives. It is our obligation to understand that in nature's shadow we all co exist.

FOOD CHAINS FOLLOW A SINGLE PATH AS ANIMALS EAT EACH OTHER.
EXAMPLE:

THE SUN provides food for GRASS
The GRASS is eaten by a GRASSHOPPER
The GRASSHOPPER is eaten by a FROG
The FROG is eaten by a SNAKE
The SNAKE is eaten by a HAWK.

FOOD WEBS SHOW HOW PLANTS & ANIMALS ARE INTERCONNECTED BY DIFFERENT PATHS.
EXAMPLE:

TREES produce ACORNS which act as food for many MICE and INSECTS.
Because there are many MICE, WEASELS and SNAKES have food.
The insects and the acorns also attract BIRDS, SKUNKS, and OPOSSUMS.
With the SKUNKS, OPPOSUMS, WEASELS and MICE around, HAWKS, FOXES, and OWLS can find food.
They are all connected! Like a spiders web, if one part is removed, it can affect the whole web.

FOOD WEBS show how plants and animals are connected in many ways to help them all survive. FOOD CHAINS follow just one path of energy as animals find food.

Ecosystem

Definition

noun, plural: ecosystems

A system that includes all living organisms (biotic factors) in an area as well as its physical environment(abiotic factors) functioning together as a unit.

Supplement

An ecosystem is made up of plants, animals, microorganisms, soil, rocks, minerals, water sources and the local atmosphere interacting with one another.

Word origin: coined in 1930 by Roy Clapham, to denote the physical and biological components of an environment considered in relation to each other as a unit.
Related phrases: ecosystem model, ecosystem ecology, ecosystem diversity.
See also: biotic factor, abiotic factor, ecology.

Abiotic Components

These include the non-living, physico - chemical factors such as air, water, soil and the basic elements and compounds of the environment.

Abiotic factors are broadly classified under three categories.

Climatic factors which include the climatic regime and physical factors of the environment like light, humidity, atmospheric temperature, wind, etc.

Edaphic factors which are related to the structure and composition of soil including its physical and chemical properties, like soil and its types, soil profile, minerals, organic matter, soil water, soil organisms.

Inorganic substances like water, carbon, sulphur, nitrogen, phosphorus and so on. Organic substances like proteins, lipids, carbohydrates, humic substances etc.

Biotic Components

It comprises the living part of the environment, which includes the association of a number of interrelated populations belonging to different species in a common environment.

The populations are that of animal community, plant community and microbial community.

Biotic community is distinguished into autotrophs, heterotrophs and saprotrophs.

Autotrophs (Gr: auto - self, trophos - feeder) are also called producers, convertors or transducers.

These are photosynthetic plants, generally chlorophyll bearing, which synthesize high-energy complex organic compounds (food) from inorganic raw materials with the help of sunlight, and the process is referred as photosynthesis.

Autortophs form the basis of any biotic system.

In terrestrial ecosystems, the autotrophs are mainly the rooted plants.

In aquatic ecosystems, floating plants called phytoplankton and shallow water rooted plants called macrophytes are the dominant producers.

Heterotrophs (Gr: heteros - other; trophs - feeder) are called consumers, which are generally animals feeding on other organisms.

Consumer's also referred as phagotrophs (phago - to ingest or swallow) or macroconsumers are mainly herbivores and carnivores.

Herbivores are referred as First order consumers or primary consumers, as they feed directly on plants.

For e.g., Terrestrial ecosystem consumers like cattle, deer, rabbit, grass hopper, etc.

Aquatic ecosystem consumers like protozoans, crustaceans, etc.

Carnivores are animals, which feed or prey upon other animals.

Primary carnivores or Second order consumers include the animals which feed on the herbivorous animals.

For e.g., fox, frog, predatory birds, smaller fishes, snakes, etc.

Secondary carnivores or Third order consumers include the animals, which feed on the primary carnivores.

For e.g., wolf, peacock, owl, etc.

Secondary carnivores are preyed upon by some larger carnivores.

Tertiary carnivores or Quaternary consumers include the animals, which feed on the secondary carnivores.

For e.g., lion, tiger, etc.

These are not eaten by any other animals.

The larger carnivores, which cannot be preyed upon further are called top carnivores.

Saprotrophs (Gr: sapros - rotten; trophos - feeder) are also called decomposers or reducers. They break down the complex organic compounds of dead matter (of plants and animals).

Decomposers do not ingest their food. Instead they secrete digestive enzymes into the dead and decaying plant and animal remains to digest the organic material. Enzymes act upon the complex organic compounds of the dead matter.

Decomposers absorb a part of the decomposition products for their own nourishment. The remaining substances are added as minerals to the substratum (mineralisation).

Released minerals are reused (utilised) as nutrients by the plants (producers).

Biotic and Abiotic Factors

Biotic and abiotic factors are interrelated. If one factor is changed or removed, it impacts the availability of other resources within the system.

Biotic FactorsBiotic, meaning of or related to life, are living factors. Plants, animals, fungi, protist and bacteria are all biotic or living factors.

Abiotic Factors
Abiotic, meaning not alive, are nonliving factors that affect living organisms. Environmental factors such habitat (pond, lake, ocean, desert, mountain) or weather such as temperature, cloud cover, rain, snow, hurricanes, etc. are abiotic factors.

A System
Biotic and abiotic factors combine to create a system or more precisely, an ecosystem. An ecosystem is a community of living and nonliving things considered as a unit.

The Impact of Changing Factors
If a single factor is changed, perhaps by pollution or natural phenomenon, the whole system could be altered. For example, humans can alter environments through farming or irrigating. While we usually cannot see what we are doing to various ecosytems, the impact is being felt all over. For example, acid rain in certain regions has resulted in the decline of fish population.

Abiotic and Biotic Factors

Abiotic factors are essentially non-living components that effect the living organisms of the freshwater community.

When an ecosystem is barren and unoccupied, new organisms colonising the environment rely on favourable environmental conditions in the area to allow them to successfully live and reproduce.

These environmental factors are abiotic factors. When a variety of species are present in such an ecosystem, the consequent actions of these species can affect the lives of fellow species in the area, these factors are deemed biotic factors.

This page will go into the abiotic factors of the freshwater environment which determine what sort of life would be suited to living (and adapting) to the conditions of the ecosystem.

As described in previous pages, the light from the sun is a major constituent of a freshwater ecosystem, providing light for the primary producers, plants. There are many factors which can affect the intensity and length of time that the ecosystem is exposed to sunlight;

Aspect - The angle of incidence at which light strikes the surface of the water. During the day when the sun is high in the sky, more light can be absorbed into the water due to the directness of the light. At sunset, light strikes the water surface more acutely, and less water is absorbed. The aspect of the sun during times of the day will vary depending on the time of the year.
Cloud Cover - The cloud cover of an area will inevitably affect intensity and length of time that light strikes the water of a freshwater ecosystem. Species of plants rely on a critical period of time where they receive light for photosynthesis.
Season - The 4 seasons in an ecosystem are very different, and this is because less light and heat is available from the sun in Winter and vice versa for Summer, therefore these varying conditions will affect which organisms are suited to them.
Location - The extreme latitudes receive 6 months of sunlight and 6 months of darkness, while the equator receives roughly 12 hours of sunlight and darkness each day. This sort of variance greatly affects what type of organisms would occupy freshwater ecosystems due to these differences.
Altitude - For every one thousand metres above sea level, average temperature drops by one degree Celsius. Altitude will also affect the aspect of which sunlight hits the freshwater ecosystem, therefore playing a part on which organisms will occupy it.

As you can see, many abiotic factors can play a part in determining the end product, which organisms live and succeed in the freshwater ecosystem. The sun provides light for photosynthesis, but also provides heat giving a suitable temperature for organisms to thrive in. The temperature of a freshwater environment can directly affect the environment as a whole and the organisms that occupy it.

Enzymes operate best at an optimum temperature, and any deviation from this temperature 'norm' will result in below optimum respiration in the organism. All aquatic life are ectotherms, meaning their body temperature varies directly with its environments.

Temperature affects the density of substances, and changes in the density of water means more or less resistance for animals who are travelling in the freshwater environment.

The next page will continue to look at how these abiotic factors affect the way in which organisms operate in the freshwater ecosystem. The above examples of abiotic factors involve physical characteristics of the freshwater environment, which are continued, with subsequent information studying how the chemical composition of the freshwater ecosystem also affects which organisms survive in the environment and how they cope in these conditions.

Dominance

One of Gregor Mendel's great discoveries was the Principle of Dominance. He noted that when he hybridized two parents with different versions of a particular trait, one of those versions apparently disappeared in the hybrid (heterozygous) offspring. If he then mated those offspring to each other, the vanished trait reappeared in the third generation, apparently completely unchanged despite being invisible in generation 2. He named the version of the trait which was visible in the hybrids the dominant and the one that was invisible in the hybrids therecessive.
We now know that Mendel discovered complete dominance, which is only one of several different kinds of dominance relationships. Dominance relationships result from the interactions of the gene products of different alleles of the same gene (not from interactions between different genes). Note that dominance is virtually always defined with respect to the phenotypic of the heterozygote.

Complete Dominance: If two alleles have a complete dominance relationship, the phenotype of the heterozygote will be indistinguishable from the phenotype of the homozygous dominant. For example, for one of the gerbil fur color genes, that wild type agouti/brown allele (B) is completely dominant to the black (b) allele of the same gene. BB gerbils are brown; bb gerbils are black; Bb gerbils are brown. And you can't tell by looking at a brown gerbil whether it is BB or Bb, no matter how closely or carefully you look.
Incomplete Dominance: If two alleles have an incomplete dominance relationship, the phenotype of the heterozygote will be intermediate between the phenotypes of the two homozygotes. This is often described as "blending," though the alleles themselves do not blend. The phenotype of looks like the two traits have blended together. For example, in snapdragons, one of the various genes which control flower color has two alleles, one for red flowers and one for white flowers. The two homozygous plants will produce red and white flowers, respectively. But the heterozygote will produce pink flowers--as if the two homozygous conditions were blended together like paint. In this case, the actual flower color (phenotype) probably results from varying amounts of production of the red pigment. The homozygous red plant produces a lot of the pigment, the homozygous white plant produces none of the pigment, and the heterozygote produces half as much as the homozygous red. Note that there is no dominant allele here.
Codominance: Codominance is similar to incomplete dominance in that there is no dominant allele. However, the phenotypic expression is quite different. If two alleles have a codominance relationships, in the heterozygote both alleles will be completely expressed. For example, in humand ABO blood types, two of the three alleles (the A allele, properly designated as I^A, and the B allele, properly designated as I^B) are codominant. This gene controls the deposition of antigenic markers on cells. A person with blood type A (homozygous for I^A or heterozygous for I^A and the recessive i (for O type)) has one kind of antigen marker, while a person with blood type B (homozygous for I^B or heterozygous for I^B and the recessive i (for O type)) has a slightly different kind of antigen marker. The heterozygote has blood type AB, and this person's cells have both A antigens and B antigens on their surfaces. There is no "in-between" antigen, as would be expected if the alleles showed incomplete dominance. Both of the alleles are completely expressed, and the person has both blood types at the same time.

Continuous Variation

- Small differences between individuals

- Greatly affected by environment

- e.g. height, shoe size, length of hair

- plotted on a line graph

Discontinuous Variation

- Differences that are classed or categorised

- Not greatly affected by environment

- e.g. blood group, sex, hair colour, eye colour

- plotted on a bar chart or pie chart

Friday 13 January 2012

Capacitors

A capacitor or condenser is an electrical or electronic device that can store energy.

It stores the energy within the electric field between a pair of conductors (called "plates"). The process of storing energy in the capacitor is known as "charging", and involves electric charges of equal size, but opposite charge, building up on each plate.

Once charged the plates have a uniformelectric field between them. Within the main body of the plates this field is truly uniform - but at the edges the uniformity is disrupted due to 'edge effects'. Therefore any practical work should take account of this.

Capacitors are often used in electric and electronic circuits as energy-storage devices. There are many different types but in physics questions you are usually asked about a simple parallel plate capacitor. In electronics you will learn about the many types and their uses.

If we connect up circuit A and then close the switch we would observe the bulb lighting up brightly and then getting gradually dimmer until it went out. (This would happen quickly so we would just observe a flash).

This is because the brightness of the bulb will depend upon the size of the current flowing. Initially charge would flow quickly onto the plates of the capacitor (brightly lit bulb) then, as the plates began to fill with charge, the rate of charge flow would exponetially decrease (bulb would grow dimmer) until finally the capacitor would be fully charged and no more charge woul flow (bulb would be dark).

With circuit B, however we would not even notice that the capacitor was there! the bulb would remain lit all of the time. The capacitor would never be fully charged it would be in the process of charging 50 times a second on opposite plates - therefore there would be a good rate of charge transfer (current) to keep the bulb brightly lit up.

The capacitor therefore blocks d.c. current but allows a.c. current through.

Capacitance

The capacitor's capacitance (C) is a measure of the quantity of charge (Q) stored on each plate when a given potential difference or voltage (V) is applied across the plates:

So capacitance is defined as:

The ratio of charge stored on an isolated conductor to the difference in potential.

The charge required to cause unit potential difference in a conductor

Units

In SI units, a capacitor has a capacitance of one farad (F) when one coulomb (C) of charge is stored when one volt (V) of potential difference is applied across the plates. Since the farad is a very large unit, values of capacitors are usually expressed in microfarads (

F), nanofarads (nF), or picofarads (pF).

Parallel Plate Capacitor

For parallel plate capacitors the capacitance (C) is proportional to the area of each of the conducting plates and inversely proportional to the distance between the plates - as long as the area (A)is much, much greater than the distance between the plates (d) squared.

It is also proportional to the permittivity of the dielectric (

). The dielectric is the insulator substance that separates the plates - often that is air.

The capacitance of a parallel-plate capacitor is therefore given by:

When there is a difference in electric charge between the plates, an electric field is created in the region between the plates. The electric field that created is proportional to the amount of charge that has been moved from one plate to the other. This electric field creates a potential difference V between the plates of this simple parallel-plate capacitor.

V = Ed

Thursday 12 January 2012

an extra ordinary wedsite for IGCSE

http://www.schoolphysics.co.uk/

http://www.revisiontime.com/

capacitor and capacitance

http://science.howstuffworks.com/physical-science-channel.htm

Capacitor:

Capacitor, a device whose principal electric property is capacitance, the ability to store an electric charge. They are important components in many kinds of electrical equipment, including radio and television transmitters and receivers, some automobile ignition systems, and some types of motors. An early form of capacitor, the Leyden jar, was used by 18th-century scientists in studying the nature of electricity and is used today in physics laboratory demonstrations.

The ability of a capacitor to store an electric charge is useful in controlling the flow of an electric current. In some automobile ignition systems, for example, a capacitor (called a condenser) temporarily stores a charge when the breaker points of the distributor open. If there were no condenser, the charge would jump the gap and damage the points.

Another use of capacitors is in circuits that filter electrical signals. A capacitor whose capacitance can be varied is used in the tuning circuit of radio and television receivers. Varying the capacitance changes the resonant frequency of the tuner circuit so that it matches the frequency of the desired station or channel, filtering out signals of all other frequencies.

The typical commercial capacitor consists of two plates (conductors such as metal plates or foils) separated from one another by an insulator, or dielectric, with each plate connected to a terminal. There are two principal types of capacitors, those with continuously variable capacitance and those with a fixed capacitance.

When voltage is placed across the terminals of an uncharged capacitor, charge flows up to the plates but not across the insulator; one plate receives a positive charge, the other a negative charge. As the plates become charged, a voltage is produced across them that opposes the externally applied voltage. When these two voltages have the same magnitude, the current ceases and the capacitor is said to be charged. A charged capacitor is discharged by reducing the external voltage; when this occurs, charge flows off the plates, producing a current and decreasing the voltage across the plates until the external voltage and the plate voltage are equal.

Common Commercial Capacitors

Capacitors. Three types are shown (front to back): mica, ceramic cylinder, and dielectric. The penny gives an indication of their size.

Air Capacitors

use air as the insulator. Most variable capacitors are of this type. Variable capacitors are most often made of two sets of parallel aluminum plates that are interleaved. One set of plates is fixed, while the other can be rotated. Rotation changes the effective area of the plates, thereby varying the capacitance.

Oil or Liquid Dielectric Capacitors

consist of rigid metal plates immersed in oil or some other liquid insulator. The entire unit is sealed in a leakproof container.

Mica Capacitors

A mica capacitor consists of alternate layers of mica and aluminum foil in a plastic case. Such capacitors are compact, durable, and stable; they are used in precision work.

Ceramic Capacitors

One type is a hollow cylinder of a ceramic material, forming the insulator; the plates are thin films of metal deposited on the cylinder's inner and outer surface. Another type is a block containing many plates interleaved with a ceramic material. Both types are sealed in plastic to protect them from damage and moisture. Ceramic capacitors are much used in situations involving very high frequencies, as in television sets.

Paper Capacitors

Two metal foils are separated by a layer of paper or polyester film. Another layer of paper or film is placed on the outside of one of the pieces of foil. This sandwich is rolled up, impregnated with oil, and sealed in a moisture-tight container. Paper capacitors are widely used.

Electrolytic Capacitors

One of the conductors consists of a metal—usually tantalum or aluminum—covered by a thin oxide film. The oxide film serves as the insulator separating the metal from an electrolyte or some other nonmetallic conductor. The most common type of electrolytic capacitor is a block of tantalum with numerous interconnected oxide-lined pores containing the nonmetallic conductor. Electrolytic capacitors provide a relatively large amount of capacitance for their size.

Capacitance:

Capacitance, the ability of an object or a system of objects to store an electric charge. All objects have this property to varying degrees. A familiar example of capacitance is the ability of a storm cloud to store electricity and then give it up in a bolt of lightning.

Quantitatively, the capacitance (C) of a body is defined as the ratio of the electric charge (Q) on the body to the voltage (V) of the body; that is, C = Q/V

The capacitance of a system depends upon the size, shape, and composition of the bodies in the system and their orientations with respect to one another. For example, a parallel plate capacitor—a system consisting of two identical flat, parallel metal plates separated by an insulator—has a capacitance given by the formula C = eA/d, where E is a constant that depends upon the insulator, A is the area of one of the plates, and d is the distance between the plates.

Capacitance is measured in farads (f). A parallel plate capacitor has a capacitance of 1 farad if a charge of 1 coulomb on each plate is needed to produce a voltage of 1 volt between the plates. The farad is too large a unit for practical purposes. Hence capacitance is commonly measured in millionths of a farad, or microfarads (mf).

http://science.howstuffworks.com/physical-science-channel.htm

Sunday 8 January 2012

linear graph

http://www.brightstorm.com/math/algebra/linear-equations-and-their-graphs/definition-of-slope/
http://www.brightstorm.com/math/algebra/linear-equations-and-their-graphs/finding-the-slope-of-a-line-from-a-graph/
http://www.brightstorm.com/math/algebra/linear-equations-and-their-graphs/finding-the-slope-of-a-line-from-an-equation/

Saturday 7 January 2012

http://express.smarttech.com/?url=http://exchangedownloads.smarttech.com/public/content/b3/b33f7259-4979-4296-9a8a-342a652e084b/%234%20Algebra_S3_B12_bpn_F.notebook#

Wednesday 4 January 2012

properties of waves

What is a wave?

We use the word wave in everyday conversation to refer to ocean, light, sound, or earthquake waves. But what do all of these seemingly different phenomena have in common, and why is it important to understand the nature of waves? Let's explore these topics.

Waves transmit the energy that topples buildings during an earthquake, energy that allows us to communicate in the modern world, and energy that allows for life on earth at all. Our observations of the earth from space are also dependent on waves, those that are received by satellites. Thus, waves are a basic feature of the natural world and our ability to understand waves has resulted in many useful devices, cell phones, garage door openers, and microwave ovens, to name a few. With such a variety, what do all waves have in common? Ocean, light, sound, and earthquake waves share the characteristics contained in the scientific definition of wave.

Definition
The Random House dictionary tells us that a wave is:
Physics. a progressive disturbance propagated from point to point in a medium or space without progress or advance by the points themselves, as in the transmission of sound or light.It's a wave if:
1) energy moves from one place to another and 2) matter doesn't move from one place to another, for the most part.

For example, ocean waves ceaselessly arrive at the shore without piling up infinite amounts of water. The wave arrives, but the water doesn't.

We know that ocean waves carry energy because they are able to beat up and move objects at the shore. It takes a wave the same amount of energy to move a large boulder as it would for us to do the same, manually or with a bulldozer.

In understanding the earth, it's useful to concentrate on two general classes of waves, mechanical and electromagnetic waves.

Mechanical waves
Common types of mechanical waves include sound or acoustic waves, ocean waves, and earthquake or seismic waves. In order for compressional waves to propagate, there must be a medium, i.e. matter must exist in the intervening space. For our purposes, we use the term matter to mean that atoms must exist in the intervening space. To learn more about different types of mechanical waves such as earthquake waves, link to our module on Mechanical Waves.

Electromagnetic waves
Common types of electromagnetic waves include visible light, infrared, and ultraviolet radiation, among others. The transmission of electromagnetic waves does not require a medium and electromagnetic waves are able to travel through vacuums. Unlike mechanical waves such as sound, electromagnetic waves can travel successfully across the near emptiness of outer space. Thus humanity has been entertained for eons by the stars that light night skies. To learn more about different types of electromagnetic waves such as ultraviolet radiation, link to our module on Electromagnetic Waves.

Wavelength
Wavelength is the distance between two consecutive and equivalent points on a wave. Wavelength can be quantified by measuring the distance between two equivalent and consecutive points, such as the distance between two peaks or two troughs. The scientific symbol for wavelength is a Greek letter called lambda.
Watch the animation to see examples of wavelength.

Natural waves come in many different wavelengths, covering a vast range relative to human senses of scale. Gamma rays which are a form of electromagnetic radiation have wavelengths as short as one trillionth of a meter. Tsunami waves can have wavelengths greater than 100 miles (161 km).

Amplitude
Amplitude is a measurement of the vertical distance of the wave from the average. The wave axis is the average height of the wave over one cycle, and is usually considered to be zero. Heights above and below the average are given positive and negative values, respectively.
The wave shape shown below is called a sine wave. The maximum and minimum amplitudes of this sine wave are the heights measured from the wave axis (white line) to the top of the wave peak and bottom of the wave trough. Everywhere else along the wave, amplitudes are less than the maximum.
Watch the animation to see examples of amplitude.

Bigger ocean waves have larger wave heights or amplitude. The amplitude of typical ocean waves is between 2 and 8 feet.

Frequency
Frequency is a measurement of how often a recurring event such as a wave occurs in a measured amount of time. One completion of the repeating pattern is called a cycle. Only moving waves which vary their positions with respect to time possess frequency. Frequency is one way to define how fast a wave moves.
Waves can move in two ways. The frequencies of progressive waves or those that move forward indicate how fast a wave moves forward in units of cycles per unit time. The frequencies of standing waves or those that oscillate in place are the rate of oscillation in units of cycles per unit time.

Definition
The dictionary definition of frequency is:Physics. a) the number of periods or regularly occurring events of any given kind in a unit of time, usually one second. b) the number of cycles or completed alternations per unit time of a wave or oscillation.
Symbol: f; Abbr.: freq.

Units
Frequency is expressed in units of cycles per unit time.

Although frequency is a measurement of rate of movement, it is not identical to velocity. For example, if we think of a car that moves at 60 miles per hour, we mean just that. However, if we say that a wave has a frequency of 60 cycles per hour, points on the wave may be traveling faster or slower depending on wavelength. Comparing two waves of the same wavelength, a higher frequency is associated with faster movement. Comparing two waves of different wavelengths, a higher frequency doesn't always indicate faster movement, although it can. Waves of different wavelengths can have the same frequency. For some purposes, the measurement frequency is more useful than absolute velocity.
The unit, Hertz
The unit Hertz (Hz) is used to describe frequency in cycles per second. In a sentence the proper format for writing this relationship is:

One cycle represents the movement of one wavelength.
Radio call numbers
Often you might hear radio frequencies given in Megahertz (MHz) ... (under construction).
Wave period
Wave frequency is also related to another measurement called the wave period (T). The wave period is just how much time it takes for one cycle to pass and the units are always in terms of time. The faster a wave moves, its wave period becomes smaller.
Instead of measuring in terms of a fixed time unit, the second, the wave period uses a fixed number of cycles, one cycle ...

How do you measure wave period?
Wave period can be determined by measuring how much time it takes two peaks to pass a certain point. You can do this for ocean waves by standing on a pier and using a stop watch.

Tuesday 3 January 2012

ecology

Sunday 1 January 2012

variation and inheritance

What is variation?

All people are human. They belong to the same species. Your friends and classmates may have different eye colour and hair colour. Some will be boys and some will be girls. Some will be tall and some will be shorter. The presence of differences between living things of the same species is called variation.

Variation between different species is always greater than the variation within a species.

Variation and classification - Continuous & discontinuous

Some of the features of the different organisms in a species show continuous variation, and some features show discontinuous variation.

Continuous variation

Human height is an example of continuous variation. Height ranges from that of the shortest person in the world to that of the tallest person. Any height is possible between these values. So it is continuous variation.

For any species a characteristic that changes gradually over a range of values shows continuous variation. Examples of such characteristics are:

height
weight
foot length.

If you record the heights of a group of people and draw a graph of your results, it usually looks something like this:

Graph shows number of people in each height category. The graph is roughly symmetrical, with fewer people in the smaller height categories (such as up to 129cm) and fewer people in the taller hieght categories such as over 175cm. The category with the greatest number of people is 150-154cm.

The more people you measure, and the smaller the categories you use, the closer the results will be to the curved line. This shape of graph is typical of a feature with continuous variation. Weight and foot length would give graphs similar in shape to this.

Discontinuous variation

Human blood group is an example of discontinuous variation. There are only 4 types of blood group. There are no other possibilities and there are no values in between. So this is discontinuous variation.

A characteristic of any species with only a limited number of possible values shows discontinuous variation. Here are some examples:

gender (male or female)
blood group (A, B, AB or O)
eye colour.

Graph shows O is the most common blood group at over 45% of the population. Next is A, at around 40%. Third is B with just under 10%, and finally, under 5% of the population have the blood group AB

Variation and classification - Inherited & environmental

Some variation within a species is inherited, and some variation is due to the environment.

Inherited causes of variation

Variation in a characteristic that is a result of genetic inheritance from the parents is called inherited variation.

Children usually look a little like their father, and a little like their mother, but they will not be identical to either of their parents. This is because they get half of their inherited features from each parent.

Each egg cell and each sperm cell contains half of the genetic informationneeded for an individual. When these join at fertilisation a new cell is formed with all the genetic information needed for an individual.

Here are some examples of inherited variation in humans:

eye colour
hair colour
skin colour
lobed or lobeless ears.

Gender is inherited variation too, because whether you are male or female is a result of the genes you inherited from your parents.

Shows someone with blue eyes, someone with brown eyes and someone with green eyes

Shows two ears. One is lobed, the other is lobeless

Environmental causes of variation

Characteristics of animal and plant species can be affected by factors such as climate, diet, accidents, culture and lifestyle. For example, if you eat too much you will become heavier, and if you eat too little you will become lighter. A plant in the shade of a big tree will will grow taller as it tries to reach more light.

Variation caused by the surroundings is called environmental variation. Here are some other examples of features that show environmental variation:

your language and religion
flower colour in hydrangeas - these plants produce blue flowers in acidic soil and pink flowers in alkaline soil.

Both types together

Some features vary because of a mixture of inherited causes and environmental causes. For example, identical twins inherit exactly the same features from their parents. But if you take a pair of twins, and twin 'A' is given more to eat than twin 'B', twin 'A' is likely to end up heavier.

Natural selection

Within a population of animals, plants or any living organisms, there will beinherited variations. Within each species the individuals with the variations best suited to the environment will survive better than the others. More of them will survive to reproduce than the others. When they do, they pass on the genetic information for these variations to their offspring.

Species gradually evolve in this way. This process is called natural selection.

Over time a population can change so much it may even become a new species, unable to reproduce successfully with individuals of the original species.

Artificial selection

Artificial selection is when people use selective breeding to produce new varieties of a species. A variety is a type of a particular species that is different in some clear way from other varieties of that species.

For example, pedigree dogs come in lots of different varieties, called breeds of dog. They may be different colours and sizes, but they are all still dogs. They are all still the same species. Different varieties of dog have been produced by selective breeding.

Different breeds of dogs

Selective breeding of cows

Suppose you wanted a variety of cow that produced a lot of milk. This is what you could do:

choose or select the cows in your herd that produce the most milk
let only these cows reproduce
select the offspring that produce the most milk
let only these offspring reproduce
keep repeating the process of selection and breeding until you achieve your goal.

Other examples of selective breeding

The key here is to identify the feature you want, and only breed from the individuals that have that feature. Here are some examples of what selective breeding can produce:

hens that lay big eggs of a particular colour
cattle that produce lots of meat
tomato plants that produce lots of tomatoes
crops that are resistant to certain plant diseases.

Variation and classification - Genetic engineering

Variation in living organisms can also be created by genetic engineering, also called genetic modification, or just 'GM'.

Using laboratory techniques scientists can alter the genetic code within the DNA of a living organism. They can add genes from a different species to an organism's DNA

For example, GM can be used to alter the DNA in a bacterium so that it produces insulin. This is a human hormone and valuable to people with diabetes. Bacteria reproduce quickly, so a lot of insulin can be made quickly and used to help people suffering from diabetes.

Ethical questions

Some people are concerned that there may be negative aspects to GM.

For example, there are people that believe GM is unethical and should be banned.

Other people are concerned that there may be unexpected long term problems of using GM, producing changes that could not be reversed. Such changes could create new pathogens or "superweeds" by the GM organisms breeding with other species. This could cause the natural balance of living organisms in the environment to be upset.

Scientists, society and individuals need to think about the advantages and disadvantages of genetic engineering.

Variation and classification - Classifying organisms

There are millions of species on our planet. It would be difficult if we just tried to describe and name each one individually. Although species can be very different from each other, many of them have similar features that allow us to put them into groups.

Modern classification system

In the eighteenth century Carl Linnaeus started the modern system of putting species of organism into certain groups and giving them scientific names. Each species is given a name using Latin words, so that the same name can be used all over the world.

For example, the scientific name for human beings is 'homo sapiens'. Putting different species into different groups according to their features is calledclassification.