CBSE Area

1. India has more than 50,000 strains of rice. Mention the level of biodiversity it represents.  [2010]        Ans. It is a genetic variation within the species. 2. Mention the information that the health workers derive by measuring BOD of a water body.  [2009] Ans. BOD (Biological Oxygen Demand) is the amount of oxygen required for biological  oxidation of microbes in any unit volume of water. 3. State an instance where human intervention saved the forest from destruction. [2009] Ans. Chipko movement. 4. Name any two forest products, each of which is the basis for some industry. [2009] Ans.  1. Wood : Sports, furniture and paper manufacturing. 2. Resin : Turpentine industry. 5. Why are coal and petroleum considered to be non-renewable sources of energy? [2009] Ans. Coal and petroleum are considered non-renewable sources of energy because they are not  being formed continuously in nature and are, therefore, not replenished. Continuous use wil...

Guess Paper 2014 Q. (a) List the factors on which scattering of light depends. (b) What is Tyndals, effect ? Q. A student sitting on the last bench in a class room cannot read the black board clearly. (i) Name the kind of defect of vision the student is suffering from. (ii) Name the type of spherical lens he has to use to correct this defect. (iii) State two possible reasons for this defect of vision. Q. Why do stars appear to twinkle while the planets do not ? Explain with the help of diagram. Q. Explain with the help of diagram why the sun is visible to us two minutes before the actual sun-rise and two minutes after the sunset. Q. (a) What is meant by power of accommodation of eye ? A person with a defective vision cannot see objects beyond 1.2 m distinctly. What should be the type of the corrective lens used to restore proper vision ? Draw a diagram of thus corrected eye. (b) A person having presbyopia uses a bifocal lens to restore proper vision. Which part of the this lens is conv...

 CBSE PHYSICS class 10 Term-II  Board   Question   Q. What is the minimum number of rays required for locating the image formed by a convex mirror for an object ? Draw a ray diagram to show the formation of a virtual image by a convex mirror. Q. A 4.0cm tall object is placed perpendicular to the principal axis of a convex lens of focal length 20cm. If the distance of the object from the lens is 30cm, find the position, nature and size of the image. Also, find its magnification. Q. (a) 4.5cm needle is placed 12cm away from a convex mirror of focal length 15cm. Give the location of the image and the magnification. Describe what happens as the needle is moved farther from the mirror. (b) What kind of mirror is used in a solar furnace ? Give reason for using this mirror.  (c) One half of a convex lens is covered with a black paper. Will this lens produce a complete image of the object ? Justify your answer. Q. (a) When an object is placed at a distance of 60 cm f...

Q. What is minimum number of rays required for locating the image formed by a concave mirror for an object? Draw a ray diagram to show the formation of a virtual image by a concave mirror. Q. (a) A concave mirror produces three times enlarged image of an object placed at 10cm. in front of it. Calculate the focal length of the mirror. (b) Show the formation of the image with the help of a ray diagram when object is placed 6 cm away from the pole of a convex mirror. Q. (a) The refractive index of diamond is 2.42. What is the meaning of this statement? (b) What is the difference between virtual images produced by concave, plane and convex mirrors ? (c) What does the negative sign in the value of magnification produced by a mirror indicates about a image ? Q. (a) Write one use of concave mirror as well as convex mirror. (b) Draw ray diagrams for the following cases when a ray of light (i) passing through centre of curvature of a concave mirror is incident on it. (ii) parallel to principal ...

Question.    Which physical and chemical properties of the elements were used by Mendeleev in creating his periodic table? List two observations which posed a challenge of Mendeleev�s periodic law. (C.B.S.E 2009) Ans. The creation of Mendeleev�s periodic table was based upon certain physical and chemical properties. Physical properties: The atomic mass of the elements was taken into account and the elements were arranged in order of increasing atomic masses. The influences of their physical properties such as melting points, boiling points, density etc. Chemical properties:  The distribution of the elements into different groups was linked with formation of  hydrides by combining with hydrogen and formation of oxides by combining with oxygen. This is linked with the valency of the elements. The two main observations which posed challenge to Mendeleev�s periodic table are as follows. (i) Position of isotopes: Since the isotopes of an element differ in their atomic ma...