## Helical Spring

The helical spring, is the most commonly used mechanical spring in which a wire is wrapped in a coil that resembles a screw thread. It can be designed to carry, pull, or push loads. Twisted helical (torsion) springs are used in engine starters and hinges. The helical spring is suspended vertically from a rigid support. The pointer is attached horizontally to the free end of spring. A meter scale is kept vertically in such a way that the tip of the pointer is over the divisions of the scale; but does not touch the scale. Helical spring works on the…

## Newton’s Third Law of Motion

Newton’s Third Law of Motion states: ‘To every action there is an equal and opposite reaction’. The Third Law of Motion indicates that when one object exerts a force on another object, the second object instantaneously exerts a force back on the first object. These two forces are always equal in magnitude, but opposite in direction. For example, when we placed a wooden block on the ground, this block exerts a force equal to its weight, W = mg acting downwards to the ground. This is the action force. The ground exerts an equal and opposite force W’ = mg…

## Role of Carbon dioxide During Respiration

Respiration is the process during which organic food, mainly glucose that is present in the cell, breaks down into simpler substances and liberates carbon dioxide and energy. The energy released during respiration is chemical energy. There are two types of respiration- aerobic and anaerobic respiration. During aerobic respiration, complete oxidation of carbohydrates takes place. Glucose is broken down by oxygen to release energy, while carbon dioxide and water are the by-products of the reaction. Aerobic respiration occurs in plants as well as animals and takes place in the mitochondria. Sometimes there is not enough oxygen around for animals and plants…

## Boiling Point of Water

As a liquid is heated, its temperature increases and the molecules of the liquid gain energy and their kinetic energy increases. As the kinetic energy increases, the molecular motion increases and the molecules of the liquid overcome the force of attraction between them.On continuous heating, a particular temperature is reached where the molecules of the liquid leave the surface in the form of vapour to produce a pressure above the liquid equal to the atmospheric pressure and the liquid starts boiling. At this stage temperature remains stationary even on heating further. This stationary temperature at which the vapour pressure of…

## Viscosity of a Liquid

Viscosity is the property of a fluid by virtue of which an internal resistance comes into play when the liquid is in motion, and opposes the relative motion between its different layers. Thus, it is the resistance of a fluid to flow. When liquid flows over flat surface, a backward viscous force acts tangentially to every layer. This force depends upon the area of the layer, velocity of the layer, and the distance of the layer from the surface.   This video explains how to determine the coefficient of viscosity of a given viscous liquid by measuring terminal velocity of…

## Tests for Amines

Amines are derivatives of ammonia in which one or more hydrogen atoms are replaced by alkyl or aryl groups. When one of the three hydrogen atoms is replaced by alkyl or aryl group, primary amine is formed. When two of the three hydrogen atoms are replaced by alkyl or aryl group, secondary anime is formed. When all the three hydrogen atoms are replaced by alkyl or aryl substituents, tertiary amine is formed.   This video explains some simple tests of amines.

## Refractive Index of a Liquid

In optics, the refractive index or index of refraction ‘n’ of a material is a dimensionless number that describes how light propagates through that medium. If ‘i’ is the angle of incidence of a ray in vacuum (angle between the incoming ray and the perpendicular to the surface of a medium, called the normal) and ‘r’ is the angle of refraction (angle between the ray in the medium and the normal), the refractive index ‘n’ is defined as the ratio of the sine of the angle of incidence to the sine of the angle of refraction.   This video explains…

## Detection of Bile Salt in Urine

Bile is a yellow-green fluid that contains water and organic molecules such as cholesterol, bile acids, and bilirubin. In humans, the two main function of bile are digestion and absorption of fats and eliminating bile salts from the body by secretion into bile. Adult humans produce around 400 to 800 ml of bile daily. In humans and most vertebrates, bile is produced by the liver. The gall bladder holds the bile produced in the liver and when the organism eats, bile is discharged into the duodenum. The formation of bile salts starts with the breakdown of red blood cells.  …

## Chemical Tests for Acetate

Acetate is a negative ion or an anion with chemical formula CH3COO-. The neutral molecules formed by the combination of the acetate ion and a cation are commonly called as acetates. The most well known compound containing acetate ion is acetic acid. Other examples of acetate salts are sodium acetate, potassium acetate etc.   This video explains how to test the presence of acetate ion in a given salt.

## Laws of Reflection of Sound

Reflection is the change in direction of a wave front at an interface between two different media so that the wave front returns into the medium from which it originated. Common examples include the reflection of light, sound and water waves. When sound travels in a given medium, it strikes the surface of another medium and bounces back in some other direction, this phenomenon is called the reflection of sound. The waves are called the incident and reflected sound waves.   This video explains how to verify the laws of reflection of sound.

## Properties of Acetic Acid

Acetic acid is an organic acid with the formula CH3-COOH. Its functional group is carboxylic acid group. Acetic acid is a monocarboxylic acid because it contains only one COOH group. It has a sour taste and pungent smell. It is the main component of vinegar. Vinegar is typically 3-7% solution of acetic acid in water. Vinegar is mainly used as a preservative in food and in the pickling of vegetables. The water free acetic acid is known as glacial acetic acid.   This video explains how to study the following properties of acetic acid (ethanoic acid): (a) Odour, (b) Solubility…

## Embryo of Dicot Seeds

A seed is a small embryonic plant enclosed inside a seed coat. It is the ripened and fertilised ovule of gymnospermic and angiospermic plants. The embryo is an undeveloped plant inside a seed from which a new plant develops. All seeds do not have the same size, shape and colour. Plant embryos in seeds have structures called cotyledons. A cotyledon is the central portion of a seed embryo to which the epicotyls- the immature shoot, and the radicle- the immature roots, are attached. Plants are classified according to the number of cotyledons present in the embryo. If the embryo has…

## Qualitative Analysis of Carbohydrates

Carbohydrates are most abundant organic compounds found in living organisms and are composed of carbon, hydrogen and oxygen. Carbohydrates act as the primary source to provide energy for functioning of living organisms. These are called carbohydrates because they can be considered as hydrates of carbon. Generally carbohydrates are defined as polyhydroxy aldehydes or polyhydroxy ketones or the compounds which produces such products on hydrolysis. Carbohydrates are called saccharides. Some of them have sweet taste and are called sugars.   This video explains some simple tests of carbohydrates.

## Plant and Animal Tissues

A group of cells having common origin, similar structure and performing a definite function is called a tissue. Tissues are found in plants and animals. Plant tissues can be grouped into two basic types: meristematic and permanent tissues. Parenchyma and Sclerenchyma are permanent tissues. Animal tissues can be grouped into four basic types: epithelial, muscular, connective and nervous tissues. Different tissues have distinctive architecture best suited for what they do.   This video describes how to identify Plant tissues (parenchyma and sclerenchyma) and Animal tissues (striated (striped) muscle fibres and nerve cells) from the prepared slides.

## Cleaning Capacity of Soap

Ordinary water does not remove dirt from clothes or skin because the dirt present is oily or greasy in nature. Soaps are one of the most commonly used cleansing agents and are capable of reacting with water to remove dirt. Each soap molecule has a polar head group (carboxylate ion, COO- group) and a long non-polar hydrocarbon tail (R group from long chain fatty acid). The polar head attracts the polar water molecule and is called hydrophilic end and the non-polar tail attracts the water insoluble oily or greasy dirt particles. When a dirty cloth is placed in soap solution,…

## Burning of Magnesium in Air

Magnesium is an alkaline earth metal with symbol Mg. It is a silvery white metal. It is a highly inflammable metal and is easy to ignite its powdered form or thin strips. Magnesium burns in air by taking oxygen from air to form magnesium oxide which is basic in nature.   This video explains the chemical change occurs during the burning of magnesium in air.

## Preparation of Pure Sample of Ferrous Ammonium Sulphate

Ferrous ammonium sulphate is a double salt of ferrous sulphate and ammonium sulphate. It has the formula FeSO4.(NH4)2SO4.6H2O. It contains two different cations Fe2+ and NH4+. It is prepared by dissolving an equimolar mixture of hydrated ferrous sulphate and ammonium sulphate in water containing a little of sulphuric acid, and then subjecting the resulting solution to crystallization when pale green crystals of ferrous ammonium sulphate separate out.   This video explains how to prepare pure sample of ferrous ammonium sulphate (Mohr’s salt).

## Surface Tension

Surface tension is the property of a liquid, by virtue of which its free surface at rest behaves like an elastic skin or a stretched rubber membrane, with a tendency to contract so as to occupy minimum surface area. This property is caused by cohesion of molecules and is responsible for much of the behaviors of liquids. Surface tension has been well- explained by the molecular theory of matter. According to this theory, cohesive forces among liquid molecules are responsible for the phenomenon of surface tension. The molecules well inside the liquid are attracted equally in all directions by the…

## Preparation of Pure Sample of Potash Alum

Potash alum is a double salt of potassium sulphate and aluminium sulphate. It has the formula K2SO4.Al2(SO4)3.24H2O. It is prepared by dissolving an equimolar mixture of hydrated aluminium sulphate and potassium sulphate in minimum amount of water containing a little of sulphuric acid and subjecting the resulting solution to crystallization, when octahedral crystals of potash alum separate out.   This video explains how to prepare a pure sample of potash alum.

## Tests for Aldehyde

Aldehydes are organic compounds containing formyl functional group, in which the carbonyl carbon is attached to a hydrogen atom and an R group. The R group may be an alkyl or aryl group. Aldehydes are formed by replacing hydrogen atom of a hydrocarbon by the formyl group. The flavours of Almond, vanilla beans and cinnamon are due to the presence of aldehyeds.   This video explains how to identify aldehydes using some simple tests.