Thursday, January 16, 2014

CBSE BOARD EXAM 2014 Model sample Paper Solved Science (Physics and chemistry)

CBSE BOARD EXAM 2014 Model sample Paper Solved Science (Physics & chemistry) Term-II
1. Give the molecular formula and IUPAC name of a carboxylic acid used as a preservative.

Ans:  Ethanoic acid, CH3COOH

2. The ciliary muscles of a normal eye are in their : (i) most relaxed (ii) Most contracted state. In which of the two cases is the focal length of the eye lens more?

Ans: The focal length of eye lens is more when the ciliary muscles of a normal eye are in their most relaxed state

3. (a) Lithium, sodium, potassium are all metals that react with water to liberate hydrogen gas. Is there any similarity in the atoms of these elements? If yes, write the similarity.

Ans: (a) Yes. The atoms of all the three elements lithium, sodium, and potassium have one electron in their outermost shell.

(b) Both helium (He) and neon (Ne) have filled outermost shells. Helium has a duplet in its K shell, while neon has an octet in its L shell.

(b) Helium is a non-reactive gas and neon is a gas of extremely low reactivity. What , if anything, do their atoms have in common?

4. Consider the following elements: Na, Ca, Al, K, Mg, and Li.

(i) Which of these elements belong to the 3 rd period of the Modern Periodic Table?

(ii) Which of these elements belong to Group 1 of Modern Periodic Table?

Ans: 5. (i) Elements which belong to the 3rd period of the Modern Periodic Table:  Na, Mg, Al. 1

(ii) Elements which belong to Group 1 of Modern Periodic Table are: Li, Na, K.

6. (a) Why do stars twinkle whereas planets do not twinkle?

(b) What is meant by far point?

Ans: (a) Stars are very far from us and light rays cover large distances. Layers of air un evenly sprayed so  due to atmospheric refraction  light rays scattered more and give  the twinkling effect whereas planets being much closer to the earth the amount of light entering our eyes  scattered less and do not twinkle.

(b) The maximum distance up to which a normal eye can see clearly is called the far point of the eye.( infinity)

7. (i) Define power of a lens and write its S.I. unit.

(ii) The image of an object formed by a convex lens is of the same size as the object. If the image is formed at a distance of 50 cm from the lens, at what distance from the lens is the object placed? Find the focal length and power of the lens used.

Ans: (i) Power of a lens is defined as the reciprocal of the focal length. It’s S.I.  Unit is dioptre.

(ii)  v = + 50 cm  Size of image = size of object  

it means  Object is placed at 2F in front of the lens and image is formed at 2F on the other side of the lens.

2F = 50 cm,( object is placed 50 cm from the optical centre of the lens.)

Focal length of the lens, f = 50/2 = +25 cm =0 .25m

P = 1/f = 1/0.25 = 100/25 = +4 D

8. A man can read the number of a distant bus clearly but he finds difficulty in reading a book.

(i) From which defect of eye is he suffering?

(ii) What type of spectacle lens should he use to correct the defect?

Ans (a) Since the man cannot see the near by objects clearly therefore he is suffering from the defect of vision called hypermetropia.

(b) Hypermetropia can be corrected by using spectacles containing convex lens of suitable power.

9. (a) Why coal and petroleum are called fossil fuels?

(b) List the four products formed when the fossil fuels are burnt?

Ans: (a) Coal and petroleum are called fossil fuels because they are formed from the dead  remains of plants and animals millions of years ago.

(b) Products formed by burning fossil fuels are carbon dioxide, water, oxides of nitrogen and oxides of sulphur.

10. (a) Write a chemical equation to represent the reaction of ethanol with acidified solution of potassium dichromate.

(b) Write two properties of carbon which lead to the huge number of carbon compounds we see around us?

Ans:  (a) C2H5OH ------ (Acidified K2Cr2O7 + Heat) -----> CH3COOH

(b) The two properties of carbon that give rise to a large number of compounds are as follows:

(i) Catenation − It is the ability of carbon to form bonds with other atoms of carbon.

(ii) Tetravalency − with the valency of four, carbon is capable of bonding with four other atoms of carbon or atoms of some other mono-velent elements.

11. Name   (a) three elements that have a single electron in their outermost shells.

(b) two elements that have two electrons in their outermost shells.        

(c) three elements with filled outermost shells.

Ans:  (a) Lithium (Li), sodium (Na), and potassium (K) have a single electron in their outermost shells.

(b) Magnesium (Mg) and calcium (Ca) have two electrons in their outermost shells.

(c) Neon (Ne), argon (Ar), and xenon (Xe) have filled outermost shells.

12. (a) A convex mirror used in an automobile has 3 m radius of curvature. If a bus is located at 5 m from the mirror, find the position, nature and size of the image.

(b) What is the effect on the wavelength of light when it travels from rarer to denser medium?

Ans: (a) R = +3 m, f = + 1.5 m Object distance, u = -5 m   Image distance, v = ? Image size h’ =?

Using mirror formula,  v = 7.5/6.5 = +1.15 m So, The image is 1.15 m behind the mirror.

m=-v/u = - 1.15/ -5 = + 0.23

The image is virtual, upright and 23% smaller in size than the object

(b) The wavelength of light decreases when it travels from a rarer to a denser medium.

13. (a) For what position of the object does a convex lens form an erect and virtual image?

(b) What is regular reflection of light?

(c) What type of mirror is used as a shaving mirror? Support your answer with reason.

Ans. (a) when the object lies between the optical centre and the focus, convex lens form an erect and virtual image

(b) When a parallel beam of light falls on a smooth and highly polished surface, then the reflected beam is also parallel and directed in a fixed direction. Such reflection of light is called regular reflection.

(c) Concave mirrors are used as shaving mirrors to see large image of face. This is because when the face is held within the focus of a concave mirror, then an enlarged image of face is seen in the concave mirror. This helps in making a smooth shave.

14. (a) How does an eye adjust itself to deal with light of varying intensity? 
(b) Give one cause of near sightedness.

Ans:  (a) The iris of eye regulates the amount of light entering the eye by adjusting the size of the pupil. If the amount of light received by the eye is too much, then the iris makes the pupil contract and reduces the amount of light entering the eye. On the other hand, if the amount of light received by the eye is small, then the iris makes the pupil expand and more light enters the eye.

(b) Decrease of the focal length of the eye lens.

15. (a) How will you bring about the following conversions? Explain by giving suitable chemical equations.

(i) Ethanol to Ethanoic acid.  (ii) Ethanol to ethene. (iii) Ethanol to ethyl ethanoate

(b) Why do unsaturated hydrocarbons burn with a yellow flame? (c) Why soaps cannot be used in hard water?

Ans: . (a)  (i) Ethanol is converted to ethanoic acid by the oxidation of ethanol in the presence of oxidising agent like alkaline potassium permanganate or acidified potassium dichromate.

C2H5OH ----( Acidified K2Cr2O7 +Heat)--> CH3COOH

(ii) Ethanol is converted to ethene by the dehydration of ethanol in the presence of dehydrating agent conc. H2SO4

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