Sound and Frequency

         Sound is a kind of energy which is detected by the ears of living beings. Sound travels in the form of waves through the material medium and reaches our ears. These waves make our eardrums vibrate. From the inner ear, nerve messages travel to the brain and we hear the sound. Sound cannot travel without a material medium. It is of great importance to us.

             Sound is a result of vibrating energy
            Sound is produced only by the vibrating bodies but our ears cannot detect all the vibrations. Human ears are sensitive to the vibrations ranging in frequencies from 20 Hz to 20,000 Hz. This range of frequencies is called the audible range. Beyond this range of vibrations, our ears are not sensitive. However, some animals like dogs can hear the frequencies even beyond this range. The word, sound is called only to those vibrations for which our ears are sensitive.

Pitch of sound
Sound range

            The range of audible frequencies differs slightly from person to person but the common range lies between 20 Hz to 20,000 Hz.

            More is the frequency of vibrations, the sharper is the sound. High frequency voices are called high pitched sounds while low frequency sounds are called hoarse sounds. Our ears are more sensitive to the frequencies from 1000 to 4000 Hz. We can distinguish some 400,000 kinds of different sounds.

            The sounds having frequencies below 20 Hz are called infrasonic while those having frequencies above 20,000 Hz are called ultrasonic. Ultrasonic waves are very useful in scientific laboratories, diagnostic instruments and ultrasonic machines. These ultrasonic sounds can be heard by dogs, bats etc. sound is produced through many sources. Infact, any vibratory thing can produce sound. Musical instruments also produce different kinds of sounds. The sound which is not pleasant to the ears is called noise.

Acid Rain Causes

          The term acid rain refers to the fall of acids mixed with rain and snow. The main cause of acid rain is the gases emitted by the factories and motor vehicles which pollute the atmosphere. Mainly sulphur dioxide is responsible for acid rain which is produced in the burning of fossil fuels. This gas is also produced by natural phenomena like volcanic corruptions; forests fires etc. sulphur dioxide reacts with water vapor and forms sulphuric acid in the presence of sunlight. This acid gets mixed with rain water or snow flakes and fall on to the earth. Similarly, motor vehicles burn petrol and diesel and produce oxides of nitrogen. These oxides produce nitric acid with rain water. In 1872, Robert Angus smith was the first person to discover acid rain.

 Emissions of sulfur dioxide and nitrogen oxides react with water vapor in the atmosphere to create sulfuric and nitric acids
Acid Rain has reduced the sparkle of the Taj Mahal
            The acid rain may occur thousand of kilometer away from the source of gas emission. During the gulf war many oilfield caught fire and the smoke produced was so much that it reached even up to the Kashmir valley and turned the snow into black. Acid rain badly affects the marine life. The reproduction capability of fish gets reduced. Trees defoliate before time and the crops having edible roots get destroyed. The Taj Mahal at Agra and New York’s statue of liberty has lost their luster due to acid rain. Water lily plants get most affected by acid rain.


A little less than one-third of the earth’s surface is land mass and the rest is covered by water. There are seven large continuous land masses called continents. They are: Asia, Europe, Africa, North America, South America, Australia and Antarctica.

            According to the German geologist, Alfred Wegener, once the earth was a single land mass known as Pangaea. Nearly 200 million years ago this land mass broke into two parts- Laurasia and Gondwana land.

            According to Wegener’s continental drift theory, these two large land masses continued to drift away from each other. Present North America and Eurasia Europe and Asia emerged out of Laurasia, while the South America, Africa, Australia and Antarctica owe their existence to the Gondwana land. Thus the seven continents of the world appeared.

            The theory also explains that not only the continents but also the crust plates, which include both the continents and the oceans, drift. Thus the continents are undergoing changes even now. In fact, earthquakes are also caused due to the drifting of these crust plates.

Caves and Caverns

A cave is a natural opening in the earth that is big enough for a person or animal to enter. Most caves are formed by the erosive action of rain water or underground water on rocks such as limestone or dolomite. The water contains dissolved carbon dioxide which forms dilute carbonic acid. This acid dissolves the rock, forming passages and large open spaces. Caverns, caves and joint galleries are the result of this process.

            The other types of caves are lava caves, ice caves and sea caves. Lava caves are found near the base of volcanic mountain. Ice caves are formed within glaciers. Sea caves are formed in the coastal rocks by the action of sea waves.

            The early man lived in caves. Even today, some groups of people in Spain and the Philippines live in caves. Kentucky caves in the USA are well known such as the mammoth cave system which is the deepest cave in the world (563, 270 meters) deep and the fisher ridge cave system is the world’s longest cave, about 116 kms long. In India, the Ajanta and Ellora caves are quite popular.

Caverns are formed by the erosive action of rain or underground water
 Caves are formed by the erosive action of rain or underground water

Journey to the Moon

The three manned Apollo-11, which had enough space for astronauts to not only move about but also to stand erect within it, set out on a journey to the moon on July 16, 1969. The special feature of Apollo’s landing on the moon was that its two astronauts could touch the surface of the moon with the help of the four legged lunar module Eagle.

At 10.56 pm on July 20, 1969. Neil Armstrong set his foot on the surface of the moon. He was the first human being to put his foot on the moon.

            In his radio communication sent to the earth Neil Armstrong described it as one small step for (a) man, one giant leap for mankind. Therefore, Edwin Aldrin stepped out on the moons surface. Michael Collins remained aboard the Apollo 11 command module in orbit. The two astronauts spent around 2 hours 30 minutes on the moon. During this period, they collected samples of moon’s rocks and soil weighing over 20 kg.

            The total estimated expenditure on this US space programme at sending men to the moon, with Apollo 17 was around 2,554.1 million dollars. With a view to reduce expenditure space shuttle was invented by the US scientists. Space shuttle is a reusable manned space vehicle with a speed of about 28,000 km. per hour. The first space shuttle Columbia was launched on April 12, 1981. The USSR launched a similar space vehicle named buran in September 1988 which returned to the earth safely after successfully completing the mission.

            After the success of this mission, the following persons made journey to the moon under the Apollo programme. They brought with them rocks and soil weighing 3,800 kg.

Apollo 12        : Conrad, Bean, Gordon November 14,     1969
Apollo 14        : Shepard, Mitchell, Roosa January 31, 1971
Apollo 15        : Scott, Irwin, Worden July 26, 1971
Apollo 16        : young, Duke, Mattingly II april 16, 1972
Apollo 17        : Cernan, Schmitt, Evans December 7, 1972

Apollo-11 Moon Landing
 Apollo 11 Lunar Module
Neil Armstrong set his foot on the Moon on July 20, 1969
Surface of the Moon

The Plants Kingdom – Algae

Algae are the simplest kinds of plants. They contain chlorophyll; therefore, they can make their food by photosynthesis. They lack vascular bundles, i.e. they do not posses xylem and phloem. Their thallus lacks true roots, shoots and leaves algae include unicellular plants to very big multicellular plants. They do not form embryo after sexual reproduction. Commonly, algae are colored and they can grow up to 40 or 60 meters in length.

            Most algae grow in rivers, ponds, lakes and oceans. Some can live in moist places on land, mountains and near trees. A few species of algae are found on the ice in the Polar Regions and in hot water springs. Some of the blue- green algae can survive even at 70-80 degree centigrade. Some algae grow on plants and a few complete their life cycle inside some plants. Many algae are saprophytic and parasitic. The best known algae are probably the seaweed found at beaches.

            About 25-30 species of algae are used as food by man. The algae porphyra of phiopcae class is a common meal in Japan. In china, Nostoc commune is used as food. In India, algae are used to prepare ice-cream, chocolate milk, gelatin and beer. Some algae are poisonous in nature and can paralyze a person.

            We get carbohydrate, vitamins A, B, C, D, E and other materials from algae. Fish depend on algae for their food. Many algae obtained from oceans are rich sources of iodine, potassium and other minerals. Algae are a good fertilizer also. The red algae grow in large colonies and turn the water red. Some red algae also form islands.
Different species of algae

Poisonous Plants

The flowers and fruits of some plants look very beautiful and attractive but they may be poisonous. A few famous poisonous plants are the following.

            Strychnos nux-vomica is a poisonous plant found in Asian countries. Its fruit is of the size of an orange and it contains five seeds in it. Strychnine poison is prepared form these seeds. This poison stops respiration and causes death.

            The white flowers which flourish on the hemlock plant produce an unpleasant smell. A poison called caniine is obtained from its roots and seeds. This poison paralyses all the organs of the human body and causes death. The great Greek philosopher, Socrates had been given a cup of hemlock to drink as punishment.

            Colchicine poison is obtained from the seeds of meadow saffron plant. This poison is used for the treatment of arthritis.

            Apart from these plants, foxglove, monkshood, poppy, cherry laurel, thorn apple, caper spurge, laburnum, henbane, holly, honey suckle, buckthorn, toadstool, bittersweet, etc. are also famous poisonous plants. Many varieties of mushrooms are also poisonous. Many plants of the subhax group are also poisonous, which produce blisters on the skin coming in contact with it. Ivy is also a poisonous plant and produces allergy in the body.

Hemlock Plant
Honeysuckle Flower

 Holly Plant
Meadow Saffron

Strychnos Nux-Vomica Plant


Environment - Ozone Depletion

According to meteorological researches the atmosphere is divided into five thermal zones- the troposphere- 10 km above the sea level; stratosphere 10 to 40 km; mesosphere 40 to 70 km; ionosphere 70 to 400 km; and exosphere above 400 km.

 Ozone Depletion - Effects of CFCs

            Stratosphere contains negligible amount of water vapor and dust. Strong jet streams blow in this layer which affects the weather of the earth. For convenience this layer may be divided into two parts called stratospheric layer and ozonosphere. Stratospheric layer exists only up to 25 km height and its temperature remains almost constant. Ozonosphere contains ozone and it exists between 25 km to 40 km. ozone is essential to life on earth because it acts as a safety shield for the earth. Ozone forms a hot layer by absorbing about 90% of short ultraviolet rays of sun which are harmful for the life on earth.
Ozone Depletion

            In nature ozone is formed from oxygen by ultraviolet radiations of the sun. These two gases remain in equilibrium or balanced condition. But recently oxygen-ozone balance has been upset by the excessive presence of chemical pollutants in the atmosphere. Scientists believe that ozone layer is becoming this over Antarctica.

            Man made chemicals especially chlorofluorocarbons adversely affect the ozonosphere. Freon gas is also a chlorofluorocarbon which is used in refrigerators. These chemicals are also used in air-conditions, aerosol spray and plastic foams. Free chlorine atoms of these compounds have disturbed the ozone equilibrium. Ozone depletion will cause dreadful disease like skin cancer and skin allergies. It may also have hazardous effect on plants and other animals. To save our earth we have to discover substitutes for chlorofluorocarbons which do not cause ozone depletion in atmosphere.

Tallest Trees

Pine, spruce, fir, cedars, juniper, cypresses etc. Are the famous coniferous trees. These trees bear unisexual cones. Male and female cones can be formed on the same plant or on different plants. The leaves of all coniferous plants are simple and they remain on the plants through the year. Therefore, these trees are called evergreen trees.

            The tallest trees of the world belong to this group. The red wood trees are considered to be the tallest of the world. These trees are now found only on the coastal regions of California. Their average height exceeds 90 meters and diameter is up to 5 meters. Their age is around 4,000 years. The tallest tree of this group was found in California in 1963. At that time, its tip was dried and its height was 112.10 meters. In 1970, its height was 111.60 meters. The tree is gradually drying up. The world’s tallest tree that is alive and is in good condition is the general Sherman of California, which is 85 meters tall. The trunks stem of these tress are used to build and cover roads.

            Among the flowering plants, eucalyptus regnans with broad leaves is the tallest tree of the world and present in Tasmania. It is 99 meters high.

Heights of some other plants:

Callie grass (5.5 meter)
Saguaro cactus (16 meters)
Tree fern (18 meters)
Bamboo (37 meters)
Giant kelp (60 meters)