CBSE ADDA

Atmospheric Refraction related question for CBSE Board CBSE NCERT Physics Class 8 and class 10 chapter light 1. A student sitting at the back of the classroom cannot read clearly the letters written on the blackboard. What advice will a doctor give to her? Ans: The student is suffering from myopia (near sightedness). Doctor advises her to use a concave lens of appropriate power to correct this defect.   2. How are we able to see nearby and also the distant objects clearly? Ans: Human eye is able to see nearby and distant objects clearly by changing the focal length of the eye lens using its power of accommodation. 3. A person needs a lens of power –4.5 D for correction of her vision. (a) What kind of defect in vision is she suffering from? (b) What is the focal length of the corrective lens? (c) What is the nature of the corrective lens? Ans: (a) Negative sign of power of lens indicates that focal length is negative that is only possible in concave lens that is used for c

SECTION - A   (Reading – 20 Marks)    1. Read the poem given below and complete the sentences that follow.   Just for a handful of silver he left us,   Just for a riband to stick in his coat-   Found the one gift of which fortune bereft us,   Lost all the others she lets us devote;   They, with the gold to give, doled him out silver,   So much was theirs who so little allowed;   How all our copper had gone for his service!   Rays- were they purple, his heart had been proud,   We that had loved him so, followed him, honoured him,   Lived in his mild and magnificent eye,   Learned his great language, caught his clear accents,   Made him our pattern to live and to die   He alone breaks from the van and the freemen,   He alone sinks to the rear and the slaves !                                                         Robert Browning   (A) The person who left them is their ___________ .   (B) He left them for the sake of __________ .   (C) The speaker and his comrades w

Q. 1. A concave mirror of focal length 20cm is placed 50 cm from a wall. How far from the wall an object be placed to form its real image on the wall?  Solution: V= -50 cm F= -20cm From mirror formula 1/u = 1/f – 1/v = -1/20+ 1/50 = - 3/100  U = - 33.3 cm Therefore, the distance of the object from the wall x =  50 – u X = 50 – 33.3 = 16.7 cm. Q.2. An object is placed at a distance of 40cm from a concave mirror of focal length 15cm. If the object is displaced through a distance of 20 cm towards the mirror, By how much distance is the image displaced? Answer: Here f = - 15 cm, u = - 40 cm Now 1/f = 1/u + 1/v Then 1/v = 1/f – 1/u Or V= uf/u-f =( - 40 x -15)/25 = -24 cm Then object is displaced towards the mirror let u1 be the distance object from the Mirror in its new position. Then u1 = -(40-20) = -20cm If the image is formed at a distance u1 from the mirror then v1 = u1f/u1-f = -20X-15/-20+15 = -60 cm. = - 20 x-15/-20+15 = -60 cm. Therefor

CBSE Science X Question paper of 2011 solution for preparation of 2014   1. What are the various steps in a food chain called? Solution: Trophic levels. 2. What is the important function of presence of ozone in earth’s atmosphere? Solution: The ozone layer prevents the harmful UV rays from entering into the earth’s atmosphere. 3. Write the electron dot structure of ethane molecule, C2H6 Self 4. What makes the earth’s atmosphere a heterogeneous mixture? Solution: Different gases like  oxygen, nitrogen, argon and CO 2 with other gases make the earth’s atmosphere a heterogeneous mixture. 5. List any four characteristics of a good fuel. Solution: Characteristics of a good fuel are : i. low ignition temperature. ii. High calorific value iii. Environmental friendly. iv. Easily available and accessible 6. What are non-renewable resources of energy? Give two examples of such resources. Solution: Non-renewable resources of energy are those energy resources t