Sample Guess questions 2012 term-2 Science IX - Physics

CLASS IX SUMMATIVE ASSESSMENT II SAMPLE PAPERS FOR SCIENCE
1.Science_IX_Summative Assessment Term-II- Sample Paper-I
2.Science IX Summative Assessment Term-II-Sample Paper-II
3.Science IX Summative Assessment Term-II-Sample Paper-III
4.Science IX Summative Assessment Term-II-Sample Paper- IV
5.Science X Summative Assessment Term-II-Sample Paper -V
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Guess questions term-2 Science IX SUBJECT- PHYSICS
Q1: What is the relation between speed of sound, frequency and wavelength?

Q2: Which travels faster sound of light, also discuss the speed of fastest one In solids, liquids and solids?

Q3: A source of wave produces 20 crests and 20 troughs in 0.2s. Find the Frequency of the wave?

Q4: Will a vibrating source always produce sound?

Q5: What are supersonics, infrasonic and ultrasonic waves?


Q6: Can sound waves travel through vacuum?

Q7: Does the sound of a bomb explosion travel faster than the sound produced By a humming bee?

Q8: If an observer places his ear at the end of a long pipe, he can hear two Distinct echoes when the pipe is hammered at the other end. Explain.

Q9: A ship sends out ultrasound that results from the seabed and is detected After 3.42s. If the speed of ultrasound through sea water is 1531m/s. , what is the distance of the sea bed from the ship?

Q10:What is density? Give its units.

Q11: A force of 15N is uniformly distributed over an area of 150m2. Find pressure In Pascal?

Q12: Differentiate between mass and weight?

Q13: What is the relation between thrust and pressure?

Q14: What is the relation between acceleration due to gravity and Gravitational Constant?

Q15: What happens to a body when the density of a body is equal to the density of the liquid?

Q16: A body of mass 2kg floats in a liquid, what is the buoyant force on the body?


17Q: A coolie carries a load of 50kg on his head and walks on a level road up to 100m.What is the work done by him?

18 Q: Give units of Power, Work and Energy?

19 Q: What is the commercial unit of energy?

20Q:Two bodies have their masses m1/m2 =3 and their kinetic energy E1/E2=1/3 .The ratio of their velocities are?

21Q:Prove that P=F x V where P is power, F is force and v is velocity?

22Q:An electric motor creates a tension of 4500N in hoisting a cable and reels at a rate of 2m/s. The Power of the motor is?

23 Q: State Work Energy theorem?

24. Water stored in the Bhakra dam is used to produce electric power. Explain various types of energy transformations taking place in the process.

25. How much time will a pump of 1kW power take to lift 500 litre of water to a height of 40 m? Given that density of water is 1 kg/litre and g = 10 ms-2

26.In the office room of Mohan’s father a tube of 40 W, a fan of 75 W and a cooler of 150 W have been installed. If all these appliances are used for 8 hours a day, calculate the energy consumed per day in commercial unit of energy.

26.Does the work done by gravity on an object, so as to take it to a height h, depends upon the path followed? Explain, giving an example.

CLASS VIII Subject–Science Solved LESSON-11-HUMAN EYE

Q.1. Explain the structure of eye.
Ans: The human eye is like a camera. Its lens system forms an image on a light sensitive screen called the retina.
The eye ball is approx. spherical in shape with a diameter of 2.3cm.
The human eye has the following parts:-
(a) Cornea:-The transparent spherical membrane covering the front of the eye.

(b) Iris:-The coloured diaphragm between the cornea and lens.

(c) Pupil:-The small hole in the iris.

(d) Eye lens:-Its is a transparent lens made of jelly like material.

(e) Ciliary muscles:-These muscles hold the lens in position.

(f) Retina:-The back surface of the eye.

(g) Blind spot:-The point at which the optic nerve leaves the eye. An image formed at this point is not sent to the brain.

(h) Aqueous humour:-A clear liquid region between the cornea and the lens.

(i) Vitreous humour:-The space between eye lens and retina is is filled with another liquid called Vitreous humour.

Q.2.How we are able to see in dim and bright light?

Ans: Our retina's 125 million rods are used only in dim light and help us to see in dim and bright light

Q.3.What is the function of the ciliary muscles?

Ans: Changes focal length of eye lens.
When we see distant objects, the ciliary muscles are relaxed, the lens becomes thin. This, increase focal length of lens . This enables us to see distant objects clearly.

When you are looking at objects closer to the eye, the ciliary muscles contract. The eye lens becomes thicker. Consequently, the focal length of the eye lens decreases. This enables us to see nearby objects clearly

Q.4.What kind of image is formed by eye-lens?

Ans: Real, inverted and diminished

Q.5.What are photoreceptors?

Ans: Photoreceptors are millions of specialized neurons that detect and respond to light, there are 2 types of photoreceptors called rods and cones

Q.6.How we can see colours?

Ans: We see colour because of the Rods and Cones in our eyes

Q.7.What is persistence of vision? 

The impression of image is remains on retina for about 1/16th of second is called  persistence of vision.

This is used during cinematography. The sequence of still picture taken by movie camera is projected on the screen at the rate of 24 or more images per second so that images merge in one another on screen.

Q.8.How does persistence of vision help to see the object as moving?

Persistence of vision of retina help to merge images in one another on screen help to see the object as moving .

Q.9.How we are able to see a moving picture?

Ans Due to persistence of vision of our eyes, images merge in one another with in 1/16th of second and we can see movie.

Q.10.Which principle is used in cinematography?

Ans: persistence of vision.

Q.11.What happens when an object is brought closer to the eye and why?

When an object is brought closer to the eye the ciliary muscles contract. The eye lens becomes thicker. Consequently, the focal length of the eye lens decreases. This enables us to see nearby objects clearly

Q.12 What is the far point and near point of the human eye with normal vision?

Ans: The farthest distance at which an object clearly can be seen clearly. It is infinity for normal eyes.
The nearest distance at which an eye focus image clearly of an object is called near point. It is 25 cm from the eye.

Q.13.What are the three defects of the eye?

Ans: There are mainly three common refractive defects of vision. These are (i) myopia or near-sightedness, (ii) Hypermetropia or farsightedness, and (iii) Presbyopia

Q.14.What are the different reasons for vision problems?

Ans: Myopia- This defect may arise due to (i) excessive curvature of the eye lens, or (ii) elongation of the eyeball

(b) Hypermetropia: This defect arises either because (i) the focal length of the eye lens is too long, or (ii) the eyeball has become too small

Presbyopia - It arises due to the gradual weakening of the ciliary muscles and diminishing flexibility of the eye lens

Q.15.Who developed Braille system?

Ans: The Braille system was based on a method of communication originally developed by Charles Barbier.

Q .16 Why are we not able to see immediately after we enter a darkened hall?

Ans. When we are in bright sunlight, outside a darkened hall, iris makes pupil small to receive less light. When we enter a darkened hall from out side, the eye is not able to see with the reduced amount of light entering the pupil. Depending on the darkness of the hall iris increases the size of the pupil to receive more light and then after sometime we are able to see things around us in a semi dark room also.

Q .17 why in poor light we cannot perceive the true colours of an object?

Ans. In dim light the rods are sensitive but cones are not. Cones are responsible for perception of colours.

Q. 18. Which part in the eye provides the most of refraction of the light entering the eye?

Ans. Cornea and aqueous humor.

Q. 19. Why birds wake up with sunrise and sleep in the resting place by sunset.

Ans. Their retina has cones in excess, which are sensitive to bright light only.

Q. 20. Which is the most insensitive part of the eye retina?

Ans. Blind spot is the spot on retina, which is insensitive to light.

CBSE ADDA: X Guess Sample paper Physics (Human eyes and color...

CBSE ADDA: X Guess Sample paper Physics (Human eyes and color...

Q. What is meant by power of accommodation of the eye?

Ans: The ability of the eye lens to adjust its focal length is called accommodation of the eye. Power of accommodation of an eye is also defined as the maximum variation in the power or focal length of the eye lens.

Q. What is the far point and near point of the human eye with normal vision?

Ans: The farthest distance at which an object clearly can be seen clearly. It is infinity for normal eyes.
The nearest distance at which an eyes focus image clearly. of an object. It is 25 cm from the eye.

Q. A student has difficulty reading the blackboard while sitting in the last row. What could be the defect the child is suffering from? How can it be corrected?

Ans: A student has difficulty reading the blackboard while sitting in the last row so he is suffering from near sightedness or myopia as far point of eye is infinity. This defect can be corrected by using a concave lens of suitable focal length. This defect is cased due to decrease in size of eye ball and increase in focal length of eye lens.

Q. Why is a normal eye not able to see clearly the objects placed closer than 25 cm?

Ans: A lens of eye cannot focus image clearly on retina if object is placed closer to 25cm and form blurred image .An eye lens can not decrease focal length below 25 cm Hence, eye cannot see it clearly.

Q. What happens to the image distance in the eye when we increase the distance of an object from the eye?

Ans: The image is formed on the retina even on increasing the distance of an object from the eye. For this eye lens becomes thinner and its focal length increases as the object is moved away from the eye

Q. Why do stars twinkle?

Ans: As we go higher and higher, the density of layers and refractive index decreases regularly. As the light from a star enters the different layers of the atmosphere and travel large distances before reaching the earth, it scattered none uniformly and seems twinkling where as light from planets travel shorter distance and don’t seem twinkling.

Q. Why does the Sun appear reddish early in the morning?

Ans: At the time of morning, the position of the sun is very far away from us. The sunlight travels longer distance through the atmosphere of the earth before reaching our eyes. Scattering of blue light is more than the scattering of red light due to less velocity. Due to this more red light reaches to our eyes. Hence sun appears reddish in the morning.

Q. The near point of a hypermetropic eye is 1 m. What is the power of the lens required to correct this defect? Assume that the near point of the normal eye is 25 cm.

Ans: In the problem it is given that the near point of the normal eye is 25 cm, hence u = - 25 cm.

The lens used forms its Virtual image at near point of hypermetropic eye i.e., v = - 1m = - 100 cm.

v= near point of hypermetropic eye = -1m = -100 cm

u = near point of normal eye = -25cm.

1/f = 1/v -1/u = -1/100 + 1/25 = (-1 + 4)/100 =3/100

f = 100/3 cm = 1/3 m

Power = 1/f = 1/(1/3) =3 dioptre

Q. The far point of a myopic person is 80 cm in front of the eye. What is the nature and power of the lens required to correct the problem?

Ans:This defect is corrected by concave lens. D=1/f=1/80cm=100/80m =-1.25D

Or, The far point is 80 cm the object distance is ¥

so applying lens formula 1/v - 1/u = 1/f

v = - 80 cm u = ¥

-1/80 + 1/¥ = 1/f

1/f = -1/80 (1/¥ = 0)

f = -80 cm

or -0.8 m power is = -1/0.8 = -10/8 = -1.25 D

So it would be a concave lens as it has a negative power

Q. Why a chicken can only see in bright colour?

An: The retina of chicken’s eyes has only few rod cells .Its retina has mostly cone cells. Due this it can see only in bright colour. Hence wake up late in the morning and sleep early in evening.

Q.Why does the sky appear dark instead of blue to an astronaut?

Ans. Colour of the sky is on account of scattering of light of shorter wavelengths by particles in the atmosphere of earth. If the earth had no atmosphere, there would not have been any scattering and the sky would have looked dark. When an astronaut in his spacecraft goes above the atmosphere of earth, sky appears dark to him because there is no scattering of light.

chemistry adda: CBSE BOARD EXAM 2012 Model sample Paper Solved Sc...

chemistry adda: CBSE BOARD EXAM 2012 Model sample Paper Solved Sc...: CBSE BOARD EXAM 2012 Model sample Paper Solved Science (Physics and chemistry) 1. Give the molecular formula and IUPAC name of a carboxyli...

Additional examplary multiple-choice question for assessment of practical-skills in science and technology – class X

Q1. In an experiment to determine the focal length of a concave less, a student
obtained the image of a distant window on the screen. To determine the focal length
of the less, She should measure the distance between the
(1) lens and the screen only.
(2) lens and the window only.
(3) screen and the window only.
(4) screen and the lens and also between the screen and the window.

Q.2: On the basis of their experiment ‘to trace the path of a ray of light passing
through a rectangular glass slab’ four students arrived at the following interpretations:

(1) Angle of incidence is greater than the angle of emergence.
(2) Angle of emergence is less than the angle of refraction.
(3) Emergent ray is parallel to the incident ray.
(4) Emergent ray is parallel to the refracted ray.

The correct interpretation is that of the student

(1) I       (2) II       (3) III  (4) IV

Download file containing 100 questions Download File

CBSE Science and Technology Class: X Assignments 2012

CBSE Science and Technology Class: X Assignments 2012

Chapter: CABBON and ITS COMPOUNDS

1.Write the molecular formula of ethanol.

2.An organic compound X having molecular formula C₂H₄O₂, gives brisk effervescence with sodium bicarbonate. Give the formula and the name of X.

3 The general formula of a homologous series of carbon compounds is C_nH_2n+1OH.Write the molecular formulae of fourth and fifth members of this series?

4.Illustrate the IUPAC system of nomenclature for the following compounds:

    (a).CH₃OH        (b).C₂H₈OH           (c ).C₃H₇OH.

5.What happens when a dry piece of sodium metal is added to ethyl alcohol?

Explain with equation.

6.What happens when ethyl alcohol is warmed with alkaline potassium permagnate?

7.What will be the formula and electron dot structure of Propyne?

8.Write chemical equation for saponification & esterification.

9.The molecular formula C₃H₆O can represent an aldehyde as well as a ketone.

Write their structure and name them.

10.Why should one condemn drinking of alcohol?

11.Define isomerism.

12.How is that we can use  detergents not soaps for washing clothes even when water is hard?

Assignment Subject: Class: X Chapter: Periodic Classification of Elements

1. How many elements were discovered at the time of Mendeleev?

1. Define Atomic radius and give its variation along group and period.

1. Three elements A, B and C having atomic radii 124pm, 456pm and 324pm respectively. Arrange them according to their position in group.

1. Which law was based on the notes of music?

1. State Modern periodic law.

1.  What was the main advantage of Mendleev’s periodic table?

1. What are metalloids? Explain about their position in Modern periodic table.

1. Why was it necessary to change the basis of classification from atomic weight to atomic number?

1. Two elements having atomic no.12 and 17 both belong to same period. State reason.

1. Explain how Modern periodic law was able to tell about the position of isotopes in periodic table, which cannot be explained by Mendeleev?

1. (a) State two defects of Modern periodic table.

1. What are the units of inheritance in living organisms? Where are they located?

1. Name the theory of evolution given by Charles Darwin & name the book in which it was given?                                              

1. Define Genetics. What was the contribution of Mendel in this branch of biology?

1. How do embryological studies provide evidence in favor of evolution?

1. How is artificial selection beneficial?

1. How analogous organs provide evidence in favor evolution?

1. Explain diagrammatically Mendels MONOHYBRID & DIHYBRID CROSS?

1. Humans have evolved in a tree like structure. Discuss.

1. A cross between round and wrinkled seeds produced round seeds. When these were selfed out 420 seeds 300 were round &102 were wrinkled.

1. A species give rise to new species with a complex body design. Will be better than the old species.

1. A ray of light incident normally on a mirror retraces its path. Why?

1. State mirror formula. Will focal length of mirror changes on changing the distance of the object? If not, why? What determines the focal length of the mirror?

1. What kind of lens is there in human eye? What enables the eye to focus objects at different distances?

1. Explain: a) Sun appears to rise 2 minutes before and sets 2 minutes later.What is meant by persistance of vision?

1. b) Sky appears blue.

1. c) Stars twinkle at night

1. What is meant by myopia and hypermetropia? How can the two be corrected? Explain with the help of diagram?
2. A person cannot see the object distinctly hen placed at a distance less than 100 cm. What is the power of spectacles that he should use to see clearly the objects placed at 25 cm?
3. A 14-year-old student is not able to see clearly the questions written on the blackboard placed at a distance of 5m from him (a) Name the defect of vision he is suffering from. (b) With the help of labeled ray diagrams show how this defect can be corrected (c) Name the type of lens used to correct the defect.
4. What is presbyopia? What causes presbyopia? How it can be corrected?

5. Why we are not able to see immediately after we enter a darkened hall?

(b) The atomic number of X, Y and Z are 9, 11 and 17.

i.) Which of them belong to the same group?

ii.) Which of them belong to the same period?

iii.) Which is bigger in size: X or Z and why?

12. (a) Give reason:

i). A chlorine atom is smaller than a sodium atom although atomic number of chlorine (11) is greater than sodium (17).

ii.) All elements of the same group have similar properties.

iii.) the noble gases are placed in separate group.

(b) An element X belongs to third period and group 16 of the periodic table.

i)    Write its electronic configuration and name.

ii)   What is the valency of X?

Class: X Chapter: HOW DO ORGANISMS REPRODUCE

1.What is the basic difference between asexual and sexual reproduction?

2.Which of the following organisms reproduce by asexual method? Amoeba, Cat, Birds, Hydra.

3Name one organism, each which reproduces by:

 a. Binary fission     b Spore formation        c. Budding      d. Fragmentation

4. Where are  male and female gametes formed in:

a. Human beings               b. flowering plants.

5. What is vegetative propagation? Give its two advantages.

6. Differentiate between unisexual and hermophrodite organisms.

7. Define fertilization. Where does fertilization take place in human body?

8. What are STD`s? Give 2 examples.

9. Draw labeled diagram of:  A) Human male reproduction system   b) Human female reproduction system 

10. What are male and female gonads in human beings?

11. What is pollination? Explain the 2 types of pollination.

12. Explain the structure of flower with the help of a labeled diagram.

13. Define the terms~

                a) Gestation period        b) Implantation     c) Placenta    

14. Describe the function of surgical method of birth control.

15. What is the full form of OCs? Which substances are contained in these? How do they work? 

Assignment Subject: Science and Technology Class: X Chapter: Heredity and Evolution

Assignment PHYSICS Class: X Chapter: : LIGHT: REFLECTION AND REFRACTION

3. A thin lens has a focal length of –25 cm. What is the power of the lens? Is it convex or concave?

4. A converging mirror form a real image of height 4 cm, of an object of height 1 cm placed 20 cm away from the mirror. Calculate the image distance. What is the focal length of the mirror?

5. An arrow 2.5 cm high is placed at a distance of 25 cm from a diverging mirror of focal length 20 cm. Find the nature, position and size of the image formed.

6. A pond of depth 20 cm is filled with water of refractive index 4/3. Calculate apparent depth of the tank when viewed normally.

7.Calculate the distance at which an object should be placed in front of a thin convex lens of focal length 10 cm to obtain a virtual image of double its size.

8. A concave lens of focal length 25 cm and a convex lens of focal length 20 cm are placed in contact with each other. What is the power of this combination? Also calculate focal length of this combination

Assignment Subject: Science and Technology Class: X Chapter: Our Environment

1.Which of the following materials are biodegradable? Aluminium wire, Tea leaves, Synthetic fibre and wool.

2 Arrange the following in a food chain: Fish, Algae, Small animals and Big fish.

3.Define tropic level. Draw the food chain with four tropic level.

4.In a food chain consisting of grass, frog, bird and insects, where will the concentration of the harmful chemical be maximum?

5.What is meant by bioconcentration of pestisides? Which common pestisides has accumulated in human body in considerable amounts?

6.If we use excess pestisides to protect the crops from diseases,then it may cause long term damage to mankind.Justify the statement.

7.What is the difference between food chain food web?Give suitable examples. Explain how harmful chemicals enter our bodies.

8.What is ozone and how does it affect any ecosystem?

9. Write a note on the flow of energy through different steps in the food chain.

10.Consider the food chain: Grass-Goat-Tiger.

If tiger has 30 J of energy available in this food chain, how much energy was originally available in grass?

11.What is 10%law? Explain with an example how energy flows through different tropic levels.

Assignment Subject:Class: X Chapter: Management of Natural Resources

1.Name the three R’s to save the environment. Explain each of them.

2.What is ‘Amrita Devi Bishnoi National Award’?

3.Explain the role of forests in conserving the environment. How do forests get depleted? What are its consequences?

4.What is Narmada Bachao Andolan?

5.What are the advantages of building dams?

6.How do you achieve sustainable development?

7.How is Khejari tree related to the preservation of biodiversity?

8.How do we find contamination of water?

9.How is conservation indifferent from preservation?

10.How does socio-cultural environment affect human beings?

11.Name any two wastes that can be recycled and reused.

12.How can you as an individual contribute or make a difference to the management of:

      (a) forests and wild life.            (b)water resources       (c)coal and petroleum?

CLASS X SCIENCE (Physics+Chemistry) SUMMATIVE ASSESSMENT TERM II 2014 SAMPLE PAPER- I

1. Why carbon forms strong bonds with other carbon atoms, hydrogen, oxygen, nitrogen or sulphur?

2. Name the part of eye responsible for conversion of light into electrical impulses.

3.  a. How does valency vary in a group on going from top to bottom?      b. How does atomic size vary in a period on going from left to right?

4. Write one property of hydrogen which makes it resemble with (a) Alkali metals (b) Halogens.

5. a Arrange the following common substances in the increasing order of refractive indices. Ice, Kerosene, Glass, Diamond, Alcohol, Water

b. Is it necessary that optically dense medium possesses greater mass density? Give an example.

6. On reaction with sodium hydroxide, X yielded Ethanoic acid and ethanol.

(a) Give the IUPAC name of X?   (b) Name the reaction.  (c) Give a chemical reaction for the above reaction.

7. (a) How does the electronic configuration of an atom related to its position in the Modern periodic table? Give one example.

(b) Why nitrogen is more electronegative than phosphorus?

8. A concave length has focal length of 25 cm. At what distance should the object from the lens be placed so that if it forms an image at 20 cm distance from the lens? Also find the magnification produced by the lens.

9. Give an explanation for the formation of a rainbow.

10. How are we able to see distant and near by objects clearly? Which part of eye helps in changing curvature of lens? Why no image is formed at blind spot?

11.(a) Why magnification is taken negative for real images and positive for virtual images? (2)

(b) Why convex mirror is used in rear view mirrors and not concave mirror? (2)

(c) Power of concave lens is 4.5 D. Find its focal length. (1)

12.(a) Find the size, nature and position of image formed when an object of 1 cm is placed at a distance of 15 cm from a concave mirror of focal length 10 cm. (3)

(b) Why does light travels faster in water in comparison to kerosene. (Refractive index of water and kerosene are 1.33 and 1.44 respectively)  (2)

13 . a. Which property of carbon leads to formation of large number of compounds? Define it

b. What is the functional group in the following molecules? 

i.  CH₃CH₂CH₂OH   

  ii.   CH₃COOH

c. Which of the following formula represents a saturated hydrocarbon?

C_nH _2n, C _nH_2n+1 C_n H_2n+2 C_n H_2n-2

d. What happens when methane is burnt in oxygen?

e. Why is the conversion of ethanol to Ethanoic acid an oxidation reaction?                                      

14. a. Give three points to distinguish between alkenes and alkynes.

b. Explain the mechanism of cleaning action of detergents

CLASS X SCIENCE (Physics & Chemistry) SUMMATIVE ASSESSMENT TERM II 2012 SAMPLE PAPER- I (solution)

1. Due to small size and presence of four valence electrons, carbon forms strong bonds with other carbon atoms, hydrogen, oxygen, nitrogen or sulphur. 

2. Retina. 

3. a. Valency remains same on moving from top to bottom in a particular group. This is because the outermost electronic configuration of all the elements in a group remains same. 

b. Atomic size decreases on moving from left to right in a period. This is because the number of shells remains same but the nuclear charge increases. Due to this, electrons are pulled closer to the nucleus and decrease the atomic size. 

4. Resemblance with alkali metals:  

Hydrogen has the same outermost electronic configuration as that of alkali metals.

Resemblance with halogens:

Hydrogen exists as diatomic molecule as halogens. 

5. a. In the order of increasing refractive indices:

Ice; Water; Alcohol; Kerosene; Glass; Diamond                                           

b. No, it is not always necessary.  For e.g., kerosene and turpentine oil having high refractive index are optically dense than water. But its mass density is less than that of water. That is why oil floats on the surface of water. 

6. (a) X is ethyl  Ethanoate.                

(b) It is Saponification reaction.                                  

(c) CH₃COOC₂H₅ + Na OH -----------à  C₂H₅OH + CH₃COOH                             1

7. (a) By the electronic configuration of an atom we can identify the group and period to which the atom belongs. 

For example - Oxygen has atomic number 8. Its electronic configuration is 2,6.  As it can gain two electrons to complete its octet, so it belongs to group 16 Also, since the electrons are filled in two shells. So. Oxygen belongs to the second period.                                                     

(b) As we move down the group, electro negativity of elements decreases as  the atomic size increases. Nitrogen is placed above phosphorus in group 15. So, nitrogen is more electronegative than phosphorus.        

8. A concave lens always forms a virtual, erect image on the same side of the object.

v = -20 cm, f = -25 cm, u = ?              

1/v -1/u = 1/f         

1/u = 1/(-20) – 1/(-25)         

1/u = -1/100     

u= -100cm       

Thus object distance is 100 cm.          

Magnification= v/u 

= -20/ (-100) 

= + 0.5 1  

Thus image is erect, virtual and is half of the size of object.               

9. Formation of rainbow: 

The rainbow is formed in the sky when sun shines and it is raining at the same time. The raindrops in the atmosphere act like many small prisms.        

As white light enters and leaves these raindrops the various colours present in white light are refracted by different amount due to which an arch of seven colours called rainbow is formed in the sky.      

Diagram                 

10. (a) Accommodation   

      (b) Ciliary muscles.          

      (c) No image is formed at the blind spot because no nerve cells are present there to carry the information of image to the brain.  

11. (a) Distance measured upward and perpendicular to the principal axis are  taken as positive. 

Distances measured down ward and perpendicular to the principal axis are  taken as negative.   

So magnification for a real image is taken negative and for a virtual image it is taken as positive.    

(b) A convex lens forms a virtual and small sized image of the object and concave mirror forms real and inverted image.      1

Thus by using convex mirror we can get view of wider field which is not possible in case of a concave mirror. 1

(c) Power = 1/Focal length    

Or Focal length = 1/Power       

 f= 1/4.5     

f = 0.22 cm 1         

12.   (a) Object distance, 

u = -15 cm    

Image distance, v= ?  

Focal length, f = -10 cm

Mirror formula,    

 1/v + 1/u = 1/f        

1/v + 1/ (-15) = 1/(-10)      

1/v = -1/10 + -/15   

1/v = -3+2/30      

1/v = -(1/30)    

Thus the position of image is formed on left hand side in front of the concave mirror at a distance of

30 cm, its nature will be real and inverted.                

Size of image m= -v/u            

m= - [(-30)/(-15)]         

m= -2.

Thus the size of image is 2 cm and image is real and inverted.          

(b) Refractive index of a medium= Speed of light in air/ Speed of light in medium.

So, speed of light in medium= speed of light in air/ refractive index                        

Thus speed of light will be maximum in medium having lowest refractive   index. Therefore speed of light is more in water in comparison to kerosene.             

13. (a) Catenation

The property of carbon atom to link with other carbon atoms to form large molecules is called as catenation. 

b.   i. Functional group is –OH group.          

  ii. Functional group is –COOH group.        

C. C_n H_2n+ 2 represents a saturated hydrocarbon.     

d. Methane burns in oxygen with formation of carbon dioxide and water.           

CH₄ + 2O₂ -----------à  CO₂ + 2H₂O                                                                                      

e. Conversion of ethanol to Ethanoic acid is an oxidation reaction because  oxygen is added to ethanol and Ethanoic acid is formed.                   

CH ₃CH₂ OH + O₂   ----------->    CH₃ COOH       +   H₂ O

 Ethanol                                           Ethanoic acid                                             

14. a. No. Alkene                

(1) Unsaturated hydrocarbon containing a double bond between two carbon atoms are known as alkenes.  

(2) General formula is     C_nH_2n            

 Example: Ethene, Propene               

Alkynes: Unsaturated hydrocarbons containing a triple bond between two carbon atoms are known as alkynes. 

(2) General formula is C_nH_{2n -2}        

(3) Example:  Ethyne, Propyne            

b. A detergent molecule consists of two ends – 

(a) hydrocarbon tail which is hydrophobic (water repelling) and 

(b) polar head which is hydrophilic (water attracting or loving). 

When a detergent is dissolved in water, the hydrocarbon tail aligns itself towards the dirt and ionic part aligns itself towards the water. The molecules gather together as clusters, called micelles. 

When water is agitated, the dirt suspended in the micelles is easily rinsed away. Thus, the cloth gets cleaned.