With thorough notes, solved papers, and key questions, you may improve your CBSE 10th Class Science learning experience. With this useful educational content, you can excel in your academics.
Time allowed:3 Hours Maximum Marks:80
SECTION – A
1. Why does the cord of an electric oven not glow while its heating element does ? [1]
Ans. The resistance of heating element of an electric oven is very high. As the current flows through the heating element it becomes too hot and glows red. On the other hand cord of an electric oven have low resistance hence it does not become red during the flow of current.
2. Although coal and petroleum are produced by the degradation of biomass, yet we need to conserve these resources. Why ?** [1]
SECTION – B
3. What is atmospheric refraction ? List two phenomena which can be explained on the basis of atmospheric refraction. [2]
Ans. In atmosphere, there are layers of different densities and refractive indices, when light ray is passed through these layers refraction of light takes place which is called atmospheric refraction.
Two phenomenon that can be explained on the basis of atmospheric refraction are:
- (i) Twinkling of stars.
- (ii) Early sunset and delayed sunrise.
4. Name a metal of medium reactivity and write three main steps in the extraction of this metal from its sulphide ore. [2]
Ans. Zinc
The steps involved in extraction of zinc from zinc sulphide are :
(i) Roasting of sulphide ore in the presence of air to convert it into metal oxide.
(ii) Reduction of metal oxide with carbon to get the free metal.
(iii) Refining of impure metal to get pure metal.
5. List two chemical properties on the basis of which ethanol and ethanoic acid may be differentiated and explain how. [2]
Ans. (i) Ethanol does not react with sodium bicarbonate but ethanoic acid reacts with sodium bicarbonate releasing CO2 gas.
(ii) Ethanol does not change the colour of blue litmus paper but ethanoic acid changes the colour of blue litmus to red due to presence of carboxylic acid group.
OR
Unsaturated hydrocarbons contain multiple bonds between two carbon atoms and these compounds show addition reactions. Out of saturated and unsaturated carbon compounds, which compounds are more reactive ? Write a test to distinguish ethane from ethene.
Ans. Unsaturated carbon compounds are more reactive than saturated carbon compounds. Bromine water is decolourized by ethene but there is no change of colour of bromine water with ethane.
SECTION – C
6. What happens to a beam of white light when it gets refracted through glass prism ? Which colour deviates the most and the least after refraction through a prism ? What is likely to happen if a second identical prism is placed in an inverted position with respect to the first prism. Justify your answer. [3]
Ans. When white light is refracted through a glass prism, it gets split into its constituting colours at different angles. This phenomenon is called Dispersion of Light. Example-Formation of a rainbow,
Least deviated colour is red whereas most deviated colour is violet.
When second identical prism is placed in an inverted position with respect to first prism, recombination of the spectrum will take place and white light will be obtained.
OR
A student needs spectacles of power -0.5 D for the correction of his vision.
(i) Name the defect in vision the student is suffering from.
Ans. Myopia.
(ii) Find the nature and focal length of the corrective lens.
Ans. Concave lens with the focal length of 200 cm
Given, P = -0.5 D
We have,
P = 1/f m
f = -2 m
f = -200 cm
(iii) List two causes of this defect.
Ans. Two causes of Myopia are :
(a) Elongation of eye ball.
(b) High converging power of eye lens.
7. Define a food chain. Design a terrestrial food chain of four trophic levels. If a pollutant enters at the producer level, the organisms of which trophic level will have the maximum concentration of the pollutant in their bodies? What is this phenomenon called ? [3]
Ans. It is the sequence of arrangement of living organism in a community in which one organism consumes another organism to transfer food energy.
Grass → Insect → Frog → Bird
The organism at higher tropic level will have the maximum concentration of pollutants. This phenomenon is called biological magnification.
8. What are amphoteric oxides ? Give an example. Write balanced chemical equations to justify your answer. [3]
Ans. Those oxides which behave both as acidic and basic oxides are called amphoteric oxides.
Example: Al2O3 (Alumina)
9. During the reaction of some metals with dilute hydrochloric acid, the following observations were made by a student: [3]
(a) Silver does not show any change.
(b) Some bubbles of a gas are seen when lead is reacted with the acid.
(c) The reaction of sodium is found to be highly explosive.
(d) The temperature of the reaction mixture rises when aluminium is added to the acid.
Explain these observations giving appropriate reason.
Ans. (a) Silver is covered with a thin layer of silver chloride, so it does not react with dilute hydrochloric acid.
(b) Bubbles of hydrogen gas are evolved when lead is reacted with the acid.
(c) The reaction of sodium is found to be highly explosive because sodium is very reactive in nature.
(d) The temperature of the reaction mixture rises when aluminium is added to the acid because the reaction is highly exothermic in nature.
10. Given below are the steps for the extraction of copper from its ore. Write the chemical equation of the reactions involved in each case. [3]
(i) Roasting of copper (l) sulphide.
Ans.
(ii) Reduction of copper (I) oxide from copper(I) sulphide
Ans.
(iii) Electrolytic refining.
Ans.
11. What is transpiration ? List its two functions. [3]
Ans. The evaporation of water from the aerial parts of a plant is called transpiration.
Functions of transpiration:
- (i) It helps in the upward movement of water and minerals from root to the aerial parts through the stem and in the absorption.
- (ii) It helps in cooling the plant surface. It helps in the movement of dissolved minerals from root to leaves.
OR
(a) What is translocation ? Why is it essential for plants ?
Ans. The transport of food from leaves to other parts of the plant is called translocation. Translocation is essential for plants because without it food prepared by the leaves cannot reach other parts of the plant for their growth and development.
(b) Where do the substances in plants reach as a result of translocation ?
Ans. The substances in plants reach to other tissues in plants from the leaves, fruits, seeds and other growing organs as a result of translocation.
12. What is carpel ? Write the function of its various parts. [3]
Ans. The flask-shaped organ in the centre of a flower is called carpel. It is also called as female reproductive organ of the plant.
It is made up of three parts :
- (i) Stigma is the top part of carpel and is sticky. So, it receives the pollen from the anther of stamen.
- (ii) Style connects stigma to ovary and acts as the passage for the growth of pollen tube.
- (iii) Ovary contains female gametes of the plant and helps in reproduction, it is the site of fertilization.
13. A student holding a mirror in his hand, directed the reflecting surface of the mirror towards the Sun. He then directed the reflected light on to a sheet of paper held close to the mirror. [3]
(a) What should he do to burn the paper ?
Ans. He should place the sheet of paper at the focus of the mirror to burn the paper.
(b) Which type of mirror does he have ?
Ans. He has a concave mirror.
(c) Will he be able to determine the approximate value of focal length of this mirror from this activity ? Give reason and draw ray diagram to justify your answer in this case.
Ans. Yes, the sheet of paper will start burning at the focus of the mirror which will give approximate value of focal length, i.e., the distance between mirror and the focal point where the sheet of paper starts burning.
A concave mirror forms a real image of the sun.
OR
A 10 cm tall object is placed perpendicular to the principal axis of a convex lens of focal length 12 cm. The distance of the object from the lens is 18 cm. Find the nature, position and size of the image formed.
Ans. Given: Height of object, h1 = + 10 cm.
Focal length, f = + 12 cm.
Object distance, u = – 18 cm.
From the lens fomula,
= – 20 cm
The position of image formed is at distance of 36 cm from convex lens.
Since the value of magnification is more than 1 (it is 2), the image formed is larger than object.
The minus sign of magnification shows that image is formed below the principal axis. Hence, the image formed is real and inverted.
14. What are solar cells ? Explain the structure of solar panel. List two principal advantages associated with solar cells.** [3]
15. (a) Budding, fragmentation and regeneration, all are considered as asexual mode of reproduction. Why ?
Ans. Budding, fragmentation and regeneration are considered as asexual mode of reproduction because only one parent is involved no sex cells are involved.
(b) With the help of neat diagrams, explain the process of regeneration in Planaria. [3]
Ans. Regeneration in Planaria.
Regeneration in Planaria
The process of getting back a full organism from its body parts is called regeneration. Planaria reproduces by this method in which if the body of Planaria somehow gets cut into a number of pieces, then each body piece can regenerate into a complete Planaria by growing all the missing parts.
SECTION – D
16. A 6 cm tall object is placed perpendicular to the principal axis of a concave miror of focal length 30 cm. The distance of the object from the mirror is 45 cm. Use mirror formula to determine the position, nature and size of the image formed. Also draw labelled ray diagram to show the image formation in this case. [5]
Ans. Given, Height of the object ho = 6 cm
Focal length, f = -30 cm
Object distance, u = -45 cm
Image distance, v = ?
Height of image, hi = ?
We have,
v = -90 cm
Also, we have
m = hi/ho = -v/u
hi/6 = -(-90)/-45
hi/6 = -2
hi = -12 cm.
Image is real and inverted.
OR
An object 6 cm in size is placed at 50 cm in front of a convex lens of focal length 30 cm. At what distance from the lens should a screen be placed in order to obtain a sharp image of the object ? Find the nature and size of the image. Also draw labelled ray diagram to show the image formation in this case.
Ans. Height of object ho = + 6 cm
Object distance, u = – 50 cm
Focal length, f = + 30 cm
Formation of image by a convex lens when the object is placed between its optical centre (C) and focus (F’).
Using lens formula,
∴ Image distance, v = +75 cm
Hence, image formed is virtual, erect and magnified.
17. (a) Why is the use of iodised salt advisable? Name the disease caused due to deficiency of iodine in our diet and state its one symptom.
Ans. Iodised salt is advisable because iodine is necessary for the formation of thyroxine hormone by thyroid gland. Goitre is the disease caused due to its deficiency.
Symptom: The neck of the person appears to be swollen due to the enlargement of thyroid gland.
(b) How do nerve impulses travel in the body? Explain.
Ans. Two neurons are not joined to one another completely. There is a small gap between a pair of neuron. This gap is called synapse. The nerve impulse are carried out to this gap by the help of neuro transmitter (chemical substance). The conduction of nerve impulse through the synapse takes place in the form of electrical nerve impulse. When a stimulus acts on the receptor, an electrical impulse is produced with the help of chemical reaction. This electrical impulse passes through the synapse and then to the other neuron. Thus, in this way nerve impulses travel in the body.
OR
What is hydrotropism ? Design an experiment to demonstrate this phenomenon. [5]
Ans. The movement of root of plants towards water is called hydrotropism.
Take two glass troughs A and B fill each one of them two-thirds with soil. In trough A plant a tiny seedling figure (a). In trough B plant a similar seedling and also place a small ‘clay pot inside the soil figure (b). Water the soil in trough A daily and uniformly. Do not water the soil in trough B but put some water in the clay pot buried in the soil. Leave both the troughs for a few days.
Now, dig up the seedlings carefully from both the trough without damaging their roots. We will find that the root of seedling in trough A is straight. On the other hand, the root of seedling in trough B is found to be bent to the right side (towards the clay pot containing water) figure (b)This can be explained as follows.
In trough A, the root of seedling gets water from both sides (because the soil is watered uniformly) in trough B, the roots gets water oozing out from the clay pot which is kept on the right side. So, the root of seedling in trough B grows and bends towards the source of water to the right side. The experiment shows that the root of a plant grows towards water. In other words, the root of a plant is positively hydrotropic.
18. (a) What are homologous structures ? Give an example.**
(b) “The sex of a new bon child is a matter of chance and none of the parents may be considered responsible for it.” Justify this statement with the help of a flow chart showing sex-determination in human beings. [5]
Ans. The sex of a newborn depends on what happens at the time of fertilization.
(i) If a sperm carrying X chromosome fertilizes the ovum carrying X chromosome, then the girl child will be born and the child will have XX combination of sex chromosomes.
(ii) If a sperm carrying Y chromosome fertilizes the ovum carrying X chromosome, then the child born will be a boy and the child will have XY combination of sex chromosome.
The above presentation clearly shows that it is matter of chance whether the newborn will be boy or girl and none of the parents may be considered responsible for it.
19. When do we consider a person to be myopic or hypermetropic ? List two causes of hypermetropia. Explain using ray diagrams how the defect associated with hypermetropic eye can be corrected. [5]
Ans. Myopia is the defect in vision in which a person cannot see the distant objects clearly whereas in hypermetropia is the defect in which a person cannot see nearby objects clearly.
Hypermetropia is caused due to:
- (i) Decrease in converging power of eye lens.
- (ii) Too short eye ball.
In a hypermetropic eye, the image of near by object lying at normal near point N (at 25 cm) is formed behind the retina.
Hypermetropia and its correction by using convex lens.
Hypermetropic eye can be corrected using convex lenses. When a convex lens of suitable power is placed in front of hypermetropic eye, then the diverging rays of light from the object are converged first by the convex lens used. This form a virtual image of the object at another near point N.
Now, the rays can be easily focused by the eye lens to form an image on retina.
20. What is sexual reproduction ? Explain how this mode of reproduction gives rise to more viable variations that asexual reproduction. How does this affect the evolution ?[5]
Ans. The production of new organisms from two parents by making use of their sex cells is called sexual reproduction.
In sexual reproduction more viable variations are observed than asexual reproduction as two parent are involved. In case of asexual reproduction single parent organism gives rise to offsprings which are genetically identical to their parents. This limits the scope of variation in characters of off springs. Due to sexual reproduction the extent of variation is much large and therefore choices of evolution is also high. The variations in the characters of the obtained offsprings from sexual reproduction enable them to adopt according to the environment and struggle for their existence. Over a period of time the characters accumulate within the species and the formed species gives rise to new species and this process goes on.
21. Draw the pattern of magnetic field lines produced around a current carrying straight conductor passing perpendicularly through a horizontal cardboard. State and apply right hand thumb rule to mark the direction of the field lines. How will the strength of the magnetic field change when the point where magnetic field is to be determined is moved away from the straight conductor ? Give reason to justify your answer. [5]
Ans. Maxwell’s Right Hand Thumb rule states that if current carrying wire is imagined to be held in the right hand so that thumb points in the direction of current, then the direction in which fingers encircle the wire will give the direction of magnetic field lines around the wire. If we hold the current carrying straight wire so that thumbs.
Magnetic field pattern due to a straight current-carrying wire
in upward direction points the direction of current, the direction of magnetic field lines will be anticlockwise. The strength of magnetic field is inversely proportional to the distance of the point of observation from the wire. So, as we move away from the wire the strength of magnetic field decreases.
SECTION – E
22. A teacher provided acetic acid, water, lemon juice, aqueous solution of sodium hydrogen carbonate and sodium hydroxide to students in the school laboratory to determine the pH values of these substances using pH papers. One of the students reported the pH values of the given substances as 3, 12, 4, 8 and 14 respectively. Which one of these values is not correct ? Write its correct value stating the reason. [2]
Ans. The value of pH for water is not correct. The correct value of pH of water is 7 because it has almost equal concentration of H+ and OH– due to which it is neutral.
OR
What would a student report nearly after 30 minutes of placing duly cleaned strips of aluminium, copper, iron and zinc in freshly prepared iron sulphate solution taken in four beakers ?
Ans. Aluminium displaces the iron from iron sulphate and the colour of two solution changes from green to colourless.
No change takes place when copper strip is dipped in iron sulphate solution.
No change will be observed when iron strips are dipped in iron sulphate solution.
The colour of the solution changes from green to colourless when zinc is added to iron sulphate solution.
23. What is observed when a pinch of sodium hydrogen carbonate is added to 2 mL of acetic acid taken in a test tube ? Write chemical equation for the reaction involved in this case. [2]
Ans. CO2 gas is evolved with brisk effervescence when sodium hydrogen carbonate is added to acetic acid.
24. List in proper sequence four steps of obtaining germinating dicot seeds. [2]
Ans.
- (i) The root is formed when radicle of seed grows.
- (ii) The root grows downward into the soil and absorbs water and minerals from the soil.
- (iii) The shoot is formed from the upward growth of plumule.
- (iv) The green leaves are developed when shoot comes above the ground.
OR
After examining a prepared slide under the high power of a compound microscope, a student concludes that the given slide shows the various stages of binary fission in a unicellular organism. Write two observations on the basis of which such a conclusion may be drawn.
Ans. (i) The nucleus of mature cell seems elongated and a grove is formed in cell which divides the nucleus.
(ii) A single parent divides to form two daughter cells. Constriction appears due to the division of the cytoplasm.
25. List four precautions which a student should observe while preparing a temporary mount of a leaf peel to show stomata in his school laboratory. [2]
Ans.
- (i) Freshly plucked leaf should be taken for epidermal peel.
- (ii) Hold the slide by its edges.
- (iii) Peel should be cut to a proper size.
- (iv) The peel should be allowed to dry.
26. Draw the path of a ray of light when it enters one of the faces of a glass slab at an angle of nearly 45°, Label on it (i) angle of refraction, (ii) angle of emergence and (iii) lateral displacement. [2]
Ans.
OR
A student traces the path of a ray of light through a glass prism as shown in the diagram, but leaves it incomplete and unlabelled. Redraw and complete the diagram. Also label on it ∠i, ∠e, ∠r, and ∠D.
Ans.
27. The current flowing through a resistor connected in a circuit and the potential difference developed across its ends are as shown in the diagram by milliammeter and voltmeter readings respectively : [2]
(a) What are the least counts of these meters ?
Ans. 10 mA and 0.1 V
(b) What is the resistance of the resistor ?
Ans. V = 2.4 volt, I = 250 mA = 0.25A
From Ohm’s law.
