Class 12

Previous year questions, Ray Optics, Class 12, CBSE, Physics, Chapter 9

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Previous year questions, Ray Optics, Class 12, CBSE, Physics, Chapter 9 Ray Optics and Optical Instruments Class 12 Important Questions Very Short Answer Type Question 1.Aglasslensof refractive index 1.5 is placed in a trough of liquid. What must be the refractive index of the liquid in order to mark the lens disappear? (Delhi 2008)Answer:In order …

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Environmental Issues, Class 12, Biology, CBSE

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Environmental Issues, Class 12, Biology, CBSE 2 Environmental Issues Causes of air pollution The main causes of air pollution are as follows:(a) Exhaust from Automobiles: Most of the automobiles use fossil fuels. Burning of fossil fuel releases carbon dioxide and carbon monoxide. Carbon dioxide is a greenhouse gas. Carbon monoxide is a poisonous gas even …

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Evolution-Notes

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1 Theories of Origin of Life and EvolutionTheories of Origin of Life(i) In previous days, people believed that the universe and life on it was an act and result of God’s creation.(ii) There was, however, no evidence to support these claims.(iii) The early scientists and Greeks believed that life on Earth never began on Earth …

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Evolution-Formulas

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– All formulas of the chapter at one glance. 1 Hardy-Weinberg Equilibrium Hardy-Weinberg principle states that the genetic constitution in a population remains constant if there is no external influence. This statement gives us a formula that is used to solve the numerical problems of this chapter. Check the formula and the example below. 2 Calculating …

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Evidences from morphology and anatomy

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1. Comparative morphology and anatomy of individual organ and organ systems of diverse forms of organisms reveal their phylogenetic relationships and thus provides important evidences of evolution.2. Homology is a relationship defined between structures or DNA derived from a common ancestor and illustrates descent from a common ancestor.3. A common example of homologous structures in …

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Stages in Human Evolution

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The following are the stages of human evolution: 1. Dryopithecusi) Ancestors of both man and apes. ii) Lived in China, Africa, Europe and India. iii) Predominantly herbivores2. Ramapithecusi) First remains were discovered from the Shivalik range in Punjab and later in Africa and Saudi Arabia. ii) Lived in open grasslands. iii) Thickened tooth enamel, robust jaws and shorter caninesiv) Usage of …

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Mutation theory of Hugo de Vries

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The salient features of mutation theory are as follows:1. Mutations or discontinuous variations are the raw material of evolution.2. Mutations appear all of a sudden. They become operational immediately.3. Unlike Darwin’s continuous variations or fluctuations, mutations do not revolve around the mean or normal character of the species.4. The same type of mutations can appear …

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