CBSE Sample Papers for Class 10 Science Paper 4

CBSE Sample Papers for Class 10 Science Paper 4

These Sample papers are part of CBSE Sample Papers for Class 10 Science. Here we have given CBSE Sample Papers for Class 10 Science Paper 4

Time allowed: 3 hours
Maximum marks : 80

General Instructions

• The question paper comprises two sections, A and B. You are to attempt both the sections.
• All questions are compulsory.
• All questions of Section-A and B are to be attempted separately.
• There is an internal choice in two questions of three marks each and one question of five marks.
• Question numbers 1 and 2 in Section-A are one mark question. They are to be answered in one word or in one sentence.
• Question numbers 3 to 5 in Section-A are two marks questions. These are to be answered in 30 words each.
• Question numbers 6 to 15 in Section-A are three marks questions. These are to be answered in about 50 words each.
• Question numbers 16 to 21 in Section-A are 5 mark questions. These are to be answered in 70 words each.
• Question numbers 22 to 27 in Section-B are based on practical skills. Each question is a two marks question. These are to be answered in brief.

SECTION-A

Question 1.
What is the difference in the function of trypsin and pepsin ?  [1]

Question 2.
What is regeneration and where do you see it ?  [1]

Question 3.
What is galvanisation ?  [2]

Question 4.
An object is placed at a distance of 15 cm from a convex lens of focal length 20 cm. List out the characteristics of the image formed.  [2]

Question 5.
Compare the chromosome arrangement of men and women.  [2]

Question 6.
V = \(\frac { W }{ Q } \) What does this equation tell us ? The unit of V is named after which famous
scientist ? How is potential difference measured ?  [3]

OR

The current through a 16 V tungsten filament lamp connected to a 16 V accumulator of negligible resistance is 4.0 A. Calculate:

1. The resistance of the filament,
2. The power of the lamp, and
3. The electrical energy in kWh consumed in 6 hours.

Question 7.
There are three resistors of r ohm each and a battery of E volts. How should these resistors be connected to get maximum current ? Show with a circuit diagram and find out the current drawn from the battery.  [3]

Question 8.
How does carbon manage to exist in different forms ? What are the different forms ?  [3]

Question 9.
What is water of crystallisation ? Name some elements that have these crystallisation molecules and some crystalline solids that do not contain water of crystallisation.  [3]

Question 10.
Why were objections raised to the building of dams in our country ? Which movement was Medha Patkar associated with ?  [3]

OR

What we as an individual can do to reduce our consumption of the various natural resources ?

Question 11.
What would be the consequence of a decrease in haemoglobin in our body ?  [3]

Question 12.
What is the power of accommodation of the human eye ? Why does the image distance not change even though the object distance keeps changing ?  [3]

Question 13.
pH is of great importance in our daily lives. Give three examples to prove this.  [3]

OR

A compound prepared from gypsum has the property of hardening when mixed with the right amount of water. Identify the compound and write its chemical formula. Write the chemical equation of its preparation. Mention any two uses of this compound.

Question 14.
How do Mendel’s experiments show that traits maybe dominant or recessive ?  [3]

Question 15.
What are the differences between arteries and veins ?  [3]

Question 16.
What is the role of an electric fuse in a domestic circuit ? What kind of material is used in making the fuse wire and why ?  [5]

Question 17.
Carbon compounds are poor conductors of electricity. Explain with reference to their bonding.  [5]

OR

Soaps and detergents are both types of salts. State the difference between the two. Write the mechanism of the cleansing action of soaps. Why do soaps not form lather (foam) with hard water? Mention any two problems that arise due to the use of detergents instead of soaps.

Question 18.
How we should lead our life in the present day to be more environment friendly ?  [5]

Question 19.
(a) Define optical centre of a spherical lens.  [5]
(b) A divergent lens has a focal length of 20 cm. At what distance should an object of height 4 cm from the optical centre of the lens be placed so that its image is formed 10 cm away from the lens ?
(c) Show the ray diagram for the above.

Question 20.
How did the Modem Periodic Table remove the anomalies of Mendeleev’s Periodic Table ?  [5]

Question 21.
The touch-me-not plant folds its leaves in response to touch. How does this reaction happen in the plant ?  [5]

OR

What are reflex actions ? Give examples ? Explain reflex arc by an example with labelled diagram.

SECTION-B

Question 22.
(a) An atom has an electronic configuration of 2,8,7. What is the atomic number of this element ?  [2]
(b) Can you find out the element with atomic number 17 ? What kind of bond will it form on combination with other atoms ?

Question 23.
What is a thermite reaction and where is it used ?  [2]

Question 24.
Why and how is the brain protected ?  [2]

Question 25.
When you cut open a hibiscus flower what are the major parts you see ? Draw and label them.  [2]

Question 26.
In an experiment to study the dependence of potential difference (V) on the electric current (I) across a conductor (resistor), if the circuit is on for a long time, then select two correct options from the ones given below:  [2]

1. Zero error of the ammeter will be changed.
2. Zero error of the voltmeter will be changed.
3. Value of resistance will be changed.
4. Resistor will be heated.

OR

Draw a circuit to study the dependence of current on the potential difference across a resistor.

Question 27.
An object of height 2.5 cm is placed at a distance of 15 cm from the optical centre ‘O’ of a convex lens of focal length 10 cm. Draw a ray diagram to find the position of the image formed. Mark the optical centre, ‘O’, principal focus ‘F’ and height of the image on the diagram.  [2]

ANSWERS
SECTION-A

Answer 1.
Trypsin is an enzyme found in the pancreatic juice which helps to digest proteins whereas Pepsin is an enzyme found in the stomach and it helps to digest proteins too.

Ansswer 2.
Regeneration is the ability of organisms to give rise to new individual organisms from their body parts. If an individual is cut or broken up into many pieces, these pieces can grow into separate individuals. This is seen in simple animals like Hydra and Planaria.

Ansswer 3.
Galvanisation is the process of applying a protective zinc coating to iron or steel, to prevent rusting.

Ansswer 4.
Given: u = -15 cm, ƒ= 20 cm

According to formula,

\(\frac { 1 }{ f } =\frac { 1 }{ \upsilon } -\frac { 1 }{ u } \)
\(\frac { 1 }{ 20 } =\frac { 1 }{ \upsilon } +\frac { 1 }{ 15 } \)
\(\frac { 1 }{ 20 } -\frac { 1 }{ 15 } =\frac { 1 }{ \upsilon } \)
\(-\frac { 1 }{ 60 } =\frac { 1 }{ \upsilon } \)
\(\upsilon =-60cm\)

The four characteristics of the image formed by the lens are:

• It is a virtual image.
• It is an erect image.
• It is an enlarged image.
• It is at a distance of 60 cm on the same side of the lens as the object.

Ansswer 5.
Human beings have 23 pairs of chromosomes. One chromosome of each pair is maternal and one is paternal. Of the 23 pairs, 22 pairs are called perfect pairs. One pair called the sex chromosomes are different. In women there are two X chromosomes while in men there is one X and one Y chromosome. So women are XX and men are XY.

Ansswer 6.
The given equation tells us the relationship between potential difference, charge, and work done to move the charge. The equation shows that the electric potential difference between two points in , an electric circuit carrying some current is the work done to move a unit charge from one point to another. The unit of V is named after Alessandro Volta, an Italian physicist. The S.I. unit of potential difference is volt.

OR

Given: V = 16 volt, I = 4.0 ampere, t = 6 hours

• Resistance, R = V/I = \(\frac { 16 }{ 4 } \) = 4Ω
• Power,P = V x I = 16 x 4 = 64W
• Electrical energy, W = VIt = 16 x 4 x 6 = 384 Wh = 0.384 kWh

Ansswer 7.
These resistors should be connected in parallel with the battery to get maximum current.

Let the equivalent resistance be R Ω.

\(\frac { 1 }{ R } =\frac { 1 }{ r } +\frac { 1 }{ r } +\frac { 1 }{ r } \)
\(\frac { 1 }{ R } =\frac { 1+1+1 }{ r } =\frac { 3 }{ r }\)
\(R=\frac { r }{ 3 } \)
V=I × R

According to ohm’s law,

Current(I) = E × \(\frac { 3 }{ r } =\frac { 3E }{ r } \)

Answer 8.
The process by which carbon exists in different forms is called allotropy. The different compounds have the same chemical properties but very different physical properties. Diamond and graphite are the two allotropic forms of carbon. There is a difference in the properties because of a difference in which the carbon atoms are bonded to one another. In diamond, each carbon atom is bonded to four other carbon atoms forming a rigid three-dimensional structure. In graphite, each carbon atom is bonded to three other carbon atoms in the same plane giving a hexagonal array. One of these is a double bond and thus the valency of carbon is satisfied.

Answer 9.
Water of crystallisation is the fixed number of water molecules present in one formula unit of a salt. When we heat the crystals, this water is removed and the salt turns white. 1 formula unit of CuSO₄ has 5 water molecules so it is written as CuSO₄.5H₂O. Gypsum is another salt which has water of crystallisation. It has 2 water molecules. It has the formula CaSO₄.2H₂O. The crystalline solids which do not contain water of crystallisation are NaCl, KNO₃, C₁₂H₂₂O₁₁ and KMnO₄.

Answer 10.
Dams are built to generate hydroelectric power. Water is stored in huge dams built at great heights. Since the water in the reservoir would be refilled every time it rains hydroelectric power is a renew-able source of energy. However, there are some problems associated with the construction of dams. Large areas of agricultural land and human habitation has to be sacrificed. Large ecosystems could be destroyed while submerged and rotting vegetation could give rise to greenhouse gases. Suitable and satisfactory rehabilitation of the displaced people has to be ensured. Medha Phatkar is a famous social activist and she was associated with the “Narmada Bachao Andolan” against the construction of the Sardar Sarovar project on river Narmada.

OR

As an individual we can follow the principle of reduce, recycle and reuse (3Rs strategy) to reduce our consumption of the various natural resources.

1. Reduce: We can reduce our consumption of various resources like electricity consumption by switching off unnecessary lights and fans.We can save water by immediately repairing faulty taps and should ensure there is no unnecessary wastage of water. We should not waste food and can prepare only as much as required.
2. Recycle : We must clearly segregate recyclable wastes like plastic, paper, metal and glass and use them to make something fresh instead of preparing something new.
3. Reuse: In this process, we need to find alternative uses for the things that we once considered waste. Used bottles or containers can be used to store various things at home. One side papers can be used for writing on the other side as a scribbling pad. Recycling of used things greatly reduces waste generation.
   Finally we must manage our natural resources in such a way that they shall last for the future generations and are not exploited for short time gains.

Answer 11.
A decrease in the amount of haemoglobin in our body means anaemia and a general weakness of the body. Haemoglobin is the oxygen carrying pigment of the blood. In its absence very little oxygen would be transported which means all the cells will not receive their supply of oxygen. In the absence of oxygen, food will not be oxidised and there will be no release of energy. This in turn affects the body’s ability to do work.

Answer 12.
The ability of the eye lens to adjust its focal length is called power of accommodation of the human eye.
The focal length of the human eye lens can change i.e., increase or decrease depending on the distance of the object from the eye and because of this the image distance does not change. As the distance of the object from the eye varies, the ciliary muscles modify the curvature of the lens to change its focal length.

Answer 13.
pH is important in our daily lives. It plays a role in our digestive system, self-defence of animals and
plants and in tooth decay.

1. Digestive system: Our stomach produces hydrochloric acid to help in digestion of food. Some¬times during indigestion or when a person is hungry for long too much of acid is produced and this causes pain and irritation. To neutralise this, the patient is given antacids which contains a mild base.
2. Self-defence of animals and plants : Sometimes when we are stung by a honey-bee or ants it causes pain, swelling and irritation. This is due to an acid produced at the site of the sting. For relief, baking soda is used as it contains a mild base.
3. Tooth decay: Tooth decay is caused by bacteria which produce acids using the left-over food in our mouth. This can be avoided by cleaning the mouth regularly after eating. Toothpastes are slightly basic and they neutralise the excess acid in the mouth and prevent tooth decay.

OR

Gypsum is a salt which has water of crystallisation. It has 2 water molecules as water of crystallisation. When it is heated it loses the water molecules and becomes calcium sulphate hemihydrate (CaSO₄.1/2H₂O) this is called Plaster of Paris. It is a white powder and when mixed with water it changes again to gypsum which is a hard solid mass.

Uses of Plaster of Paris:

• It is used as plaster for supporting fractured bones in the right position.
• It is used for making toys, materials for decoration and for making smooth surfaces.

Answer 14.
Mendel performed his experiments using contrasting characters of pea plants. He crossed a tall plant (TT) and a dwarf plant (tt). In the F₁ generation he found all plants to be tall. Now Mendel wanted to see if all the tall plants of F1 generation were like the tall parents. So he self-pollinated the F1 tall plants. In F2, he found 3/4^th plants were tall and rest l/4^th were dwarf. This clearly shows that though both the tall and dwarf characters were inherited in F1, only tallness trait expressed itself. This means both TT and Tt are tall plants while tt is a dwarf plant. Hence, a single copy of T is enough to express tallness while 2 copies of t are required to express dwarfness. Moreover Tt did not express any in between character. Thus Mendel’s experiments clearly show that traits could either be dominant or recessive.

Answer 15.

Arteries	Veins
(i)  Arteries have thick, elastic walls	Veins have thin walls.
(ii) Arteries carry blood from the heart to different parts of the body	Veins collect blood from different and bring it to the heart
(iii) Arteries carry pure or oxygenated blood.	Veins carry impure or deoxygenated blood.
(iv) Blood flows at high pressure in the arteries.	Blood flows at lower pressure in the veins.
(v) Arteries are placed deep inside muscles.	Veins are placed superficially.

Answer 16.
The electric fuse plays an important role in the domestic circuit. It is a safety device which is used to limit the current in an electric circuit. The use of a fuse safeguards the circuit and the appliances connected in that circuit from being damaged. The fuse is always connected in series with the device. A fuse is a short piece of wire of uniform area of cross-section and high resistance, made up of a material of low melting point, so that it may easily melt due to overheating when current in excess to the prescribed limit passes through it. Generally an alloy of lead and tin is used as the material of the fuse wire because its melting point is low and resistivity is more than that of copper, aluminium, etc.

The main fuse in domestic wiring is encased in a cartridge of porcelain of similar material with metal ends. The fuses for domestic purposes are rated as 1 A, 2 A, 3 A, 5 A, 10 A etc.

Answer 17.
Carbon compounds are poor conductors of electricity. Carbon has a valency of 4. To attain the stable configuration of noble gases, carbon atom needs to either gain or lose 4 electrons.

1. If it were to gain 4 electrons it would become C^4- anion, but this makes it difficult to hold onto the 10 electrons.
2. If it were to lose 4 electrons it would become C⁴⁺ cation, but this means a lot of energy would be required to pull out the 4 electrons and leave the carbon atom with 6 protons and 2 electrons. The easy way out is to share the 4 electrons with atoms of either carbon or other elements. The shared pair is then common to both the atoms. This bond formed by a sharing of electrons is called as covalent bond and such compounds are known as covalent compounds. As there are no charged particles available covalent compounds are poor conductors of electricity. They have low melting and boiling points too.

OR

Soap	Detergents
(i) Soaps are sodium salts of long chain carbo-benzene sulphonic acids.	Detergents are sodium salt of long chain xylic  acids.
(ii) The ionic group in soap is COONa+.	The ionic groups in detergents is S03 , Na+.
(iii) Soaps are not useful when water is hard.	Detergent can be used for washing purpose even when water is hard.
(iv) Soaps are biodegradable.	Some of the detergents are non-biodegradable.
(v) Soaps have relatively weak cleansing action.	Detergents have strong cleansing action.

Mechanism of the cleansing action of soaps : The dirt present on clothes is organic matter and insoluble in water. Therefore, it cannot be removed by only washing with water. When soap is dissolved in water, its hydrophobic ends attach themselves to the dirt and removes it from the cloth. Then, the molecules of soap arranges themselves in micelles form and traps the dirt at the centre of the cluster. These micelles remain suspended in the water. Hence, the dust particles are easily rinsed away by water.

Soaps do not form lather with hard water : Soap is a sodium or potassium salt of long chain fatty acids. Hard water contains salts of calcium and magnesium. When soap is added to hard water, calcium and magnesium ions present in water displaces sodium or potassium ion present in soap forming insoluble substance called scum. A lot of soap is wasted in this process.
Problems that arise due to the use of detergents instead of soap:

• Detergents being non-biodegradable, they accumulate in the environment causing pollution. In soil, the presence of detergents leads to pH changes making soil infertile.
• The entry of detergents into food chain leads to bioaccumulation in living beings and tends towards serious health issues.

Answer 18.
To be more environment-friendly in the present day we should make the following changes in our life-style.

1. We should use the public transport system instead of personal vehicle for commuting.
2. We should look to use non-conventional sources of energy wherever feasible.
3. We should strictly follow the policy of Reduce, Reuse and Recyle.
4. We should avoid wastage of resources in our day to day lives such as water, electricity and cooking gas.
5. While adopting a modem life style we must look at sustainable development and reduced generation of waste.
6. Let us adopt back to nature techniques wherever possible. Let us use well ventilated rooms instead of air-conditioners. Let us have a roof garden to keep our homes cool naturally.

Answer 19.
(a) Optical centre is a point on the principal axis of the lens such that a ray of light passing through it emerges parallel to its direction of incidence.
(b) Given :ƒ= – 20 cm, h_o = 4 cm and υ = -10 cm

\(\frac { 1 }{ f } =\frac { 1 }{ \upsilon } -\frac { 1 }{ u } \)
\(\frac { -1 }{ 20 } =-\frac { 1 }{ 10 } -\frac { 1 }{ u } \)
\(\frac { 1 }{ u } =-\frac { 1 }{ 10 } +\frac { 1 }{ 20 } \)
\(\frac { 1 }{ u } =\frac { -2+1 }{ 20 } =\frac { -1 }{ 20 } \)
u = 20 cm
\(m=\frac { { h }_{ i } }{ { h }_{ 0 } } =\frac { \upsilon }{ u } \)
\(\frac { { h }_{ i } }{ 4 } =\frac { -10 }{ -20 } \)
2h_i = 4
h_i = 2 cm

(c)

Answer 20.
In 1913, Henry Moseley showed that the atomic number of an element is a more fundamental property than its atomic mass. So Mendeleev’s Periodic law was modified and the atomic number was adopted as the basis of the Modern Periodic Table. Prediction of properties of elements could be made more accurately when elements are arranged on the basis of increasing atomic number. The Modem Periodic Law states that, ” properties of elements are a periodic function of their atomic numbers”.

The Modem Periodic table has 18 vertical columns called groups and 7 horizontal rows called periods. The position of an element in the Periodic Table tells us about its chemical reactivity. The valence electrons determine the kind and number of bonds formed by an element. The metallic character decreases across a period while it increases down a group. While metals occur on the left of the periodic table non-metals occur on the right side of the periodic table. In the centre there is space for the metalloids.

Answer 21.
The touch-me-not plant folds its leaves as soon as it is touched. The plant moves its leaves in response to touch. If we think about where exactly the plant is touched, and what part of the plant actually moves it is obvious that the movement happens at a point different from the point of touch. Here movement has happened at points far away from the point where it was touched. Thus information about the touch has been communicated. The plant uses electrical-chemical means to convey information from cell to cell but unlike animals there is no specialised tissue in plants for the conduction of information. Plant cells change shape by changing the amount of water in them resulting in swelling and shrinking of the leaves.

OR

Reflex action is a quick, automatic, involuntary, unconscious response in the body brought about by a stimulus. Examples of reflex action:

• Withdrawal of hand suddenly on touching a hot plate.
• Withdrawal of finger suddenly when pricked by a thorn.
• Shivering of our body on feeling cold.
• Sudden closure of our eyelids when bright light falls on our eye.

Reflex arc: It is the shortest route taken by impulse from receptor to effector.
Example: When we touch a hot plate by our finger, we instantly withdraw our hand. Here stimulus is touching a hot plate, receptors are our fingers. The specialized epithelial cells of our fingers respond to stimulus and convert into impulse. This impulse is carried by sensory neuron to spinal cord which generates a motor impulse. This impulse is carried by motor neuron to effector organ i.e., muscles of hand. Response is withdrawal of our hand.

SECTION-B

Answer 22.
(a) The electronic configuration is 2,8,7 means the atomic number is 2+ 8+ 7,
which is equal to 17.
(b) The element with atomic number 17 is chlorine (Cl). With a valency of 7 it tends to gain an electron from another combining atom so that it can get the stable octet configuration. On gaining an electron it becomes electronegative ion or anion. So it forms electrovalent or ionic bonds with other atoms.

Answer 23.
Thermite reaction is a reaction between a metal and a non-metal. During this reaction a large amount of heat is produced which changes the metal into a molten state. The reaction of aluminium with ferric oxide is a thermite reaction. It is used for welding or joining railway tracks or cracked machine parts.

Fe₂0₃ + 2Al → 2Fe + Al₂0₃ + Heat

Answer 24.
The brain is the main coordinating centre of the body. The brain and the spinal cord make up the central nervous system. The brain is a delicate organ and needs to be carefully protected. It lies inside a bony box called cranium. Further inside the cranium and around the brain there are 3 layers filled with the cerebro-spinal fluid which act as shock absorbers.

Answer 25.
On opening a section of the hibiscus flower we can see the green sepal first, then the colourful petals and next the slender stamens. The stamen or the male reproductive part consists of the anther and filament. In the centre we can see the female reproductive part called carpel. It consists of 3 parts, stigma, style and the ovary at the bottom.

Answer 26.
(c) Value of resistance will be changed.
(d) Resistor will be heated.

Answer 27.
The required ray diagram, is drawn as follows:

Given: u = -15 cm, h₀ = 2.5 cm, ƒ = 10 cm
We Know that

\(\frac { 1 }{ f } =\frac { 1 }{ \upsilon } -\frac { 1 }{ u } \)
\(\frac { 1 }{ 10 } =\frac { 1 }{ \upsilon } -\frac { 1 }{ (-15) } \)
\(\frac { 1 }{ \upsilon } =\frac { 1 }{ 10 } -\frac { 1 }{ 15 } =\frac { 1 }{ 30 }\)
Image distance, υ = 30 cm
\(\frac { { h }_{ i } }{ { h }_{ 0 } } =\frac { \upsilon }{ u } \)
\(\frac { { h }_{ i } }{ 2.5 } =\frac { 30 }{ -15 } \)
h_i = -5 cm

Therefore, a real, inverted and magnified image of size 5 cm is formed at a distance of 30 cm from the lens.

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