3. What are the values of (i) Angle of incidence and ( ii) Angle of reflection for normal incidence on a plane surface?
4. Describe ‘Total internal reflection of light’. What is the essential condition for it occurance?
5. Why does Silicon have valency 4 and Chlorine 1?
6. Use the mirror formula to show that an object lying between the pole and focus of a concave mirror, the image formed is always virtual in natur e.
7. What do you understand by periodicity? Are the prop erties of elements placed in a group same? Illustrate.
8. What was Dobereiner’s basis of classification of el ements?
9. Explain double fertilization in plants.
10. What is vegetative propagation? When is it used? Na me thee methods of vegetative propagation.
11. Explain how sexual reproduction gives rise to more viable variations than asexual reproduction. How does this affect the evolution of those organisms that reproduce sexually?
12. What is fossilization? How are fossils formed?
13. The radius of curvature of a convex mirror used on a moving automobile is 2.0 m. A truck is coming behind it at a constant distance of 3.5 m. C alculate (i) the position and (ii) the size of image relative to the size of truck. What will be t he nature of image?
14. Define (i) regular reflection and (ii) diffused ref lection. List the differences between them.
15. Pankaj is a student of class 7. He is very passiona te about doing Science experiments. Recently he visited Delhi with his parents to witness Scienc e fair. He purchased different types of lenses, mirror and other articles. One day, during games pe riod, a student of same class fell down and his lips started bleeding. On observation, it was found by physical education teacher that very fine pieces of glass, difficult to observe, stranded over there. Pankaj i mmediately rushed to Physical Lab and brought a Lens. The bigger image of stranded glass pieces eased the first aid job. Read the above passage and answer the following que stions:
(a) Name the lens or mirror brought by Pankaj.
(b) Draw the ray diagram showing formation of very big image of object by lens. What should be the position of object to get such image?
(c) What values are shown by Pankaj
16. How do we see colours? Explain the role of cells to respond (i) intensity, (ii) colour. What is colour blindness?
17. What is ten percent law? Explain with an example ho w energy flows through different trophic levels?
18. Replenishment of forests is essential. Justify the statement by giving any three reasons.
19. (a) Describe asexual reproduction in Amoeba.
(b) How does sexual reproduction in plants takes pl ace?
Or
How do Mendel’s experiments show that traits are in herited independently?
20. Draw a ray diagram to show the formation of image o f an object placed between the pole and focus of a concave mirror. Obtain the relation betw een , u v and f for a given concave mirror. State clearly the assumption involved and sign conv ention used.
Or One half of a convex les is covered with a black pa per. Will this lens produce a complete image of the object? Verify your answer experimentally. E xplain your observations.
21. Draw a ray diagram in each case to show the positio n and nature of the image formed when the object is places:
(i) At the centre of curvature of a concave mirror.
(ii) Between the pole P and focus F of a concave mirror. (iii) In front of a convex mirror.
(iv) At 2F of a convex lens.
(v) In front of a concave lens.
(i) During its passages from one medium to another, whe n does a light ray change its path?
(ii) Define the term absolute refractive index of a medi um.
(iii) With the help of a ray diagram, explain the term ‘c ritical angle’.
(iv) What is the value of refractive index of the medium if the critical angle of incident in a denser-rarer interface is equal to 45 ?
22. (a) Name the gas evolved during fermentation process ?
(b) What role is played by yeast in the conversion of cane sugar (C 12 H 22 O 11 ) to ethanol?
(c) How may the following be obtained from pure eth anol? Express chemical reactions by the chemical equations.
(i) Sodium ethoxide (ii) Ethyl ethanoate (iii) Ethanal Or
(a) Why does carbon form largest number of compounds?
(b) Why are some of these are called saturated and othe r unsaturated compounds?
(c) Which of these two is more reactive?
23. (a) Draw an electron dot structure of (i) N 2
, (ii) O 2
, (iii) CaCl 2
, (iv) Na 2 O
(b) Write IUPAC name of (i) CH 3 COCH 3
, (ii) CH 3 CH 2 CH 2 CHO (c) How will you test the presence of carboxylic ac id?
(d) Complete the following reaction: CH 3 CH 2 OH + Na
(a) Give electron dot structure of (i) CO 2 , (ii) H 2 S, (iii) CaCl 2 , (iv) AlF 3
(b) How will you differentiate between Ethane and Ethen e by a suitable chemical test? Give chemical reactions involved.
(c) Why are detergents preferred over soaps? Give two r easons.
24. Trace the events that would take place in a flower from the time the pollen grains of the same species fall on the stigma up to the completion of fertilization.
Or Discuss briefly the different types of reproduction .
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