Shikshakendra

  ~ Some Terms Related To Spherical Mirrors :  Following are some of the important terms related to spherical mirrors :  i) Pole of a mirror : The centre of the reflecting curved surface of a spherical mirror is called the pole of the mirror. It is usually represented by letter p. The point p in fig. 4.14 (a) and (b), represents the pole of a concave mirror and a convex mirror. It should be noted that the pole of a spherical mirror is also called vertex of the mirror.    ii) Centre of curvature : It is the centre of hollow sphere of glass of which the spherical mirror forms a part. It is represented by the letter C.  It should be noted that the centre of curvature is not a part of the mirror. It lies outside its reflecting surface. The centre of curvature of a concave mirror lies in front of it [see Fig. 414 (a)]. However, it lies behind the mirror in case of a convex mirror [see Fig. 4. 14 (b)]. iii) Radius of curvature: The radius of the sphere of which t...

2.   Phenolphthalein: Phenolphthalien is a colourless substance. It is a synthetic indicator which is prepared in the laboratory or manufactured in the industry. In acidic solution, it remains colourless . However, adding a drop of phenolphthalein to a basic solution, turns the solution pink .  3. Methyl orange : it is also a synthetic indicator manufactured in industry or prepared in the laboratory. Methyl orange is an orange colour dye. When a drop of methyl orange is added to an acidic solution, it turns the solution red . On adding a drop of methyl orange to a basic solution, the solution turns yellow .   The colour changes of phenolphthalein and methyl orange in the acidic and basic (alkaline) solutions are given in the table 2.4 :  Let as discussed an experiment to understand the role of indicators in the identification of acid and basic solutions. EXPERIMENT :   To test acids and bases in the laboratory using change acid-base indicators. Collect the ...

~INDICATORS TO TEST ACIDS AND BASES  Some substances change their colour (or odour) on addition of an aqueous solution of an acid or base. These substances are called (acid-base indicators) . Using these substances, it is possible to identify acids and bases. Acid-base indicators are generally coloured organic substances. Well known three indicators are Litmus, phenolphthalein and methyl orange. Litmus is a natural indicator ( i.e., found in nature in plants) while phenolphthalein and methyl orange are synthetic indicators ( i.e., synthesised in the laboratory). Let us discuss them, one by one. 1) Litmus : Litmus is a natural indicator. It is extracted from lichen  a plant belonging to the division Thallophyta. The colour of Litmus solution is purple and it is neither acidic nor basic. It is neutral. In the acidic solution, it turns red while in the basic solution, it turns blue. Most often, instead of using the litmus solution as such, two types of Litmus solutions are used k...

  (ii) Mineral Acids :  The acids formed from minerals present in the earth's crust are known as mineral acids. Nitric acid was the first mineral acid. Later on, sulphuric acid and hydrochloric acid were discovered. These mineral acids much stronger than ethanoic acid and allow more chemical reactions to take place. Many chemical discoveries are based on the use of these acids.  In everyday life, we used a number of acids. Hydrochloric acid is used in cleaning kitchen sinks and sanitary wares. It is worth to note that hydrochloric acid is produced in our stomach also. Sulphuric acid is used in batteries of inverters, cars, buses, trucks, etc. Nitric acid is used by goldsmiths for cleaning gold and silver ornaments. Given in table 2.2 are the important mineral acids with their chemical formulae. From the above discussion, we find that one element is common to all the acids, which is hydrogen. Thus, we can say that presence of hydrogen is essential for a substance to act as...

~ INTRODUCTION  There are a large number of compounds in which some are organic (obtained from animals and plants) and other are inorganic (obtained from Minerals and rocks). These compounds and present in the food materials and in a number of other materials as well which we use in our everyday. On the basis of their chemical properties (such as test, order, etc.) all the compounds can be classified into the following three categories:   i)Acids, ii)Bases, and iii)Salts. In this chapter, we shall study all the three types of compounds ( i. e., acids, bases and salts) in more details. Also, we shall discuss the common characteristics of acids and bases, and their chemical nature.  ~ ACIDS  The term acid was originally used to describe any substance which had a sour taste.  The world acid has been derived from the Latin word acids, which means sour . Many fruits are sour because they contain acid. A few more examples of acidic substances  used in everyday ...

Nastic movements Movements that occur in response to a stimulus but whose direction of movement is independent of the direction of stimulus are known as nastic movements. These movements are independent of Growth. 1. Seismonasty         It refers to movements which occur in response to touch.  When the leaves of touch-me-not plant are touched, the leaves fold and droop down.  2. Nyctinasty       It refers to movements in response to day and night. These are also called sleep movements. The movements of leaves and flowers in response to day and night belongs to this category. Phytohormones or plant Hormones Phytohormones are organic substances, other than nutrients, which in low concentrations, regulate plant growth and differentiation. Plant Hormones can be divided into two main types :  Growth promoters which have a positive effect on a process and thus promote it and growth inhibitors which have negative effect on a process And th...

Electricity  Matter is composed of atoms. Electric charge, just like mass, is the basic property of a matter.  Charge originate in an atom, in which its most familiar Carriers are the electron and proton. There are two types of charges.  1. Positive  2. Negative  Charge carried by an electron is deemed negative and that carried by a proton is positive.  By convention the charge acquired by glass rod with silk is called positive charge.  While the charge produced on an ebonite road when it is rubbed with a wollen cloth is called negative charge.  A body gets positively charged when it loses electrons and negatively charged when it gains electrons. Properties of electric charge  1. Like charges         Like charges repel each other l, while unlike charges dissimilar or opposite or of different type attract each other. It means that a positive charge and a negative charge repels a negative charge. On other hand a positiv...

Spinal cord The spinal cord is a long unsegmented cord like structure. It extends from medulla of brain through vertebral canal of vertebral column of backbone. Like brain it is also protected by three meanings and cerebrospinal fluid.  The spinal cord is hollow from inside and contains a cavity called central canal. Functions   •  It conducts impulses to and from the brain.    •  It acts as reflex centre which controls all the spinal reflexes. Peripheral Nervous system All the whitish, thread like nerves which connects the various body parts with central nervous system, collectively constitute the peripheral Nervous system.  It consists of cranial and spinal nerves. 1. Cranial Nerves           Those nerves which arise from the brain are called cranial or cerebral nerves.  In men there are 12 pairs of cranial Nerves. They leave the cranium through apertures and innervate may be sensory, motor or mixed in nature. ...