Atomic spectra is the study of atoms (and atomic ions) through their interaction with electromagnetic radiation. We all know about the refraction of light. When light travels from one medium to another, it either bends towards the normal or away from the normal. The phenomenon of refraction is mainly attributed to the difference in the speed of light in various mediums. The speed of light depends upon the nature of the medium through which it passes.

The union of two sets is a new set that contains all of the elements that are in at least one of the two sets. The union is written as  A∪B

The intersection of two sets is a new set that contains all of the elements that are in both sets. The intersection is written as A∩B

A biome can be defined as a large biological community or an ecosystem where different types of living organisms including plants, animals, birds, insects, and humans are used to living in a certain type of climate.

Ecosystems are of two major types:
Terrestrial and aquatic. Terrestrial ecosystem can be further be classified into ‘biomes’.
A biome is a plant and animal community that covers a large geographical area.
The boundaries of different biomes on land are determined mainly by climate.
A biome can be defined as the total assemblage of plant and animal species interacting within specific conditions.
These include rainfall, temperature, humidity and soil conditions.
Some of the major biomes of the world are: forest, grassland, desert and tundra biomes.
Aquatic ecosystems can be classed as marine and freshwater ecosystems. Marine ecosystem includes the oceans, estuaries and coral reefs. Freshwater ecosystem includes lakes, ponds, streams, marshes and bogs.

Salient features of accounting are

• Accounting principles must  be feasible, predictable, and applicable. This must be easy to apply in the accounting system and must be easy enough to be implemented by everyone
• Accounting is special in that it documents all financial transactions. It offers a framework for the accurate recording of the transaction that businesses may make use of. The recording is systematic and is necessary for anyone who is knowledgeable in accounting standards and laws.
• Accounts include the classification into a separate group/category of all financial transactions. These categories are grouped in accordance  to their similarities in one place.
• Accounting has a feature of repeatability because of established procedures and formulae. The steps in accounting are calculated based on fixed formulas.
• The accounting principles are considered to be helpful and provide the individual important information. There are several sections and headings for the multiple transactions to make it easier for the finder to  to locate a particular transaction
• Any specialist will read and understand a description of the financial statement. The definition is identical and does not distinguish between individuals or auditors. It remains constant regardless of the person interpreting it that gives accounting the feature of universality.
• Accounting is known to provide summaries of relevant and complex financial statements. Statements of fund flow, balance sheet, and cash flow, are summarised simply and presented to the investors and the public. These statements are useful for investors to make investing decisions
• The statements made by a qualified auditor or bookkeeper for the financial department may be audited for authenticity and verified. All entries in the accounting system are linked to the company's business operation, and a financial statement offers an overview of the organisation's performance

plane angle : It usually refers to an angle in 2 dimensional figure like square, triangle, circle etc .

solid angle: It refers to an angle in 3 dimensional figure like cube,cuboid,sphere etc.

A Constitution is necessary because of the following reasons:

• It is an important law of the land. It determines the relationship of the citizens with the governments.
• It lays down principles and guidelines which are required for people belonging to different ethnic and religious groups to live in harmony.
• It specifies on how the Government would be elected and who will have the power and the responsibility to take important decisions.
• It outlines the limits on the power of the Government and tells us about the rights of the citizens.
• It expresses the aspirations of the people about creating a good society.

• Some hyphae are continuous tubes filled with multinucleated cytoplasm, these are called coenocytic hyphae and others have septae or cross walls in their hyphae.
• The cell walls of fungi are composed of chitin and polysaccharides.

The process of digestion in the buccal cavity: The buccal cavity performs two major functions, mastication of food and facilitation of swallowing. The teeth and the tongue with the help of saliva masticate and mix up the food thoroughly. Mucus in saliva helps in lubricating and adhering the masticated food particles into a bolus. The bolus is then conveyed into the pharynx and then into the oesophagus by swallowing or deglutition. The bolus further passes down through the oesophagus by successive waves of muscular contractions called peristalsis. The gastro-oesophageal sphincter controls the passage of food into the stomach. The saliva secreted into the oral cavity contains electrolytes and enzymes, salivary amylase and lysozyme. The chemical process of digestion is initiated in the oral cavity by the hydrolytic action of the carbohydrate splitting enzyme, the salivary amylase. About% of starch is hydrolysed here by this enzyme (optimum pH 6.8) into a disaccharide-maltose. Lysozyme present in saliva acts as an antibacterial agent that prevents infections.