CBSE Sample Papers for Class 10 Science Set 6 with Solutions

Students must start practicing the questions from CBSE Sample Papers for Class 10 Science with Solutions Set 6 are designed as per the revised syllabus.

CBSE Sample Papers for Class 10 Science Set 6 with Solutions

Time: 3 Hours
Maximum Marks: 80

General Instructions:

1. This question paper consists of 39 questions in 5 sections.
2. All questions are compulsory. However, an internal choice is provided in some questions. A student is expected to attempt only one of these questions.
3. Section A consists of 20 objective type questions carrying 1 mark each.
4. Section B consists of 6 Very Short questions carrying 02 marks each. Answers to these questions should be in the range of 30 to 50 words.
5. Section C consists of 7 Short Answer type questions carrying 03 marks each. Answers to these questions should be in the range of 50 to 80 words.
6. Section D consists of 3 Long Answer type questions carrying 05 marks each. Answer to these questions should be in the range of 80 to 120 words.
7. Section E consists of 3 source-based/case-based units of assessment of 04 marks each with sub-parts.

Section – A

Select and write the most appropriate option out of the four options given for each of the questions 1 – 20.
There is no negative mark for incorrect response.

Question 1.
What is the shape of the image of a distant flag, shown below, when you focus it on a screen using a convex lens?

Answer:

Explanation: As the image is focused on the screen, then the image formed is real. And real images are inverted.

Question 2.
The ability of metals to be drawn into thin wire is known as
(a) ductility
(b) malleability
(c) sonorousity
(d) conductivity
Answer:
(a) ductility
These all are physical properties of metals, The ability of metals to be drawn into thin wire is known as ductility.

Question 3.
The image formed on the retina of the human eye is :
(a) Virtual and erect
(b) Real and inverted
(c) Virtual and inverted
(d) Real and erect
Answer:
(b) Real and inverted
Explanation: The image formed on the retina of the human eye is real and inverted. On the retina, the image is converted into electrical impulses and sent to the brain. The brain flips that image into a virtual and erect image.

Question 4.
Which of the following is an example of an amorphous form of carbon?
(a) Wood
(b) Oil
(c) Chalk
(d) Coke
Answer:
(d) Coke
Coke is an example of an amorphous form of carbon that is obtained as a residue in the destructive distillation of coal.

Question 5.
Identify A, B, and C in the given diagram and match the labelling referred to in column I and correlate with the function in column II.

Column I	Column II
A.	(i) Special reproductive female sex cell which combines with male gamete to form the zygote.
B.	(ii) A male gamete moves down through it towards the female gamete in the ovary.
C.	(iii) Receiving the pollen grains from the anther of stamen during pollination.

(a) A – (iii), B – (ii), C – (i)
(b) A – (ii), B – (i), C – (iii)
(c) A – (i), B- (ii), C -(iii)
(d) A – (iii), B – (i), C – (ii)
Answer:
(a) A – (iii), B – (ii), C – (i)
Explanation: A – Stigma. The top part of the carpel is called the stigma. Stigma is for receiving the pollen grains from the anther of stamen during pollination.

B – Pollen tube. When a pollen grain falls on the stigma, it bursts open and grows a pollen tube downward through the style towards the female gamete in the ovary. A male gamete moves down the pollen tube.

C – Female gamete (ovum). It is a special reproductive female sex cell that combines with the male gamete to form a zygote.

Question 6.
A jewelry-making unit tested a few elements based on their physical properties.

Properties	A	B	C	D
Malleable	Yes	No	No	Yes
Ductile	Yes	No	No	Yes
Lustre	Yes	No	Yes	No
Melting Point	High	Low	Low	High

Which of the above elements were discarded for usage by the company?
(a) A, B, and D
(b) B, C, and D
(c) A and C
(d) B and C
Answer:
(b) B, C, and D
The elements B, C, and D were discarded for usage by the company because for making jewellery, the element should be malleable, ductile, and lustrous, and should have a high melting point. So, these properties were only seen in element A. So, the rest of the others were discarded.

Question 7.
An electric fuse is connected with :
(a) live wire
(b) earthing
(c) neutral wire
(d) parallel to the line wire
Answer:
(a) live wire
Explanation: An electric fuse is connected with live wire because it gets blown up when an excess current tries to pass through it to save the electrical appliances by restricting the flow of that current,

Question 8.
The diagram given below shows the inheritance of flower colour in pure-breeding roses.

Which of the following flowers are heterozygous for colour in the F₂ generation?
(a) A and C
(b) A and B
(c) C only
(d) B and C
Answer:
(d) B and C
When a pure-breed red colour flower crosses with a pure-breed white colour flower, then F1 progeny results in all heterozygous red flowers. When the F₁ generation is allowed to cross only B and C will be heterozygotes.

Question 9.
Which of the following terms does not represent electrical power in a circuit?
(a) I²R
(b) IR²
(c) VI
(d) V²/R
Ans.
(b) IR²
Explanation:
We know that,
P =VI …………. (i)
Where, P = Power
V = Potential difference
I = Current
V = IR ……………. (ii)
On substituting equation (ii) in equation (i), we get
P = I²R ………….. (iii)
Again, from Ohm’s law
I = \(\frac{\mathrm{V}}{\mathrm{R}}\) ……….. (iv)
On substituting equation (iv) in equation (i), we get,
P = \(\frac{\mathrm{V}^2}{\mathrm{R}}\)
Hence, option (b) IR² does not represent power.

Question 10.
Name the type of movement that helps the food to move through the digestive tract.
(a) Amoeboid movement
(b) Peristaltic movement
(c) Ciliated movement
(d) Pseudopodial movement
Answer:
(b) Peristaltic movement
Peristaltic is a series of wave-like muscle contractions that move food through the digestive tract.

Question 11.
Let us consider the flow of the current through a metallic wire if the temperature of the entire system increases. What will happen from the following options?
(a) Potential difference (V) increases
(b) Resistance (R) decreases
(c) Potential difference (V) decreases
(d) V and R remain the same
Answer:
(c) Potential difference (V) decreases
Explanation: If the temperature of the entire system increases when the current flows through a metallic wire, the power (VI) is dissipated in the form of heat. Hence the potential difference (V) decreases.

Question 12.
Which of the following correctly defines autosomes?
(a) Chromosomes that do not play any role in sex determination
(b) Chromosomes which play a role in determining the sex of the newborn
(c) Both (a) and (b)
(d) Neither (a) nor (b)
Answer:
(a) Chromosomes that do not play any role in sex determination
Autosomes are the chromosomes that do not play a role in sex determination.

Question 13.
Which of the following properties of aluminium makes it suitable for making cooking utensils?
(i) Good thermal conductivity
(ii) Good electrical conductivity
(iii) Ductility
(iv) High melting point
(a) (i) and (ii)
(b) (i) and (iii)
(c) (ii) and (iii)
(d) (i) and (iv)
Answer:
(d) (i) and (iv)
Explanation: Good thermal conductivity and a high melting point of aluminium are the properties that make it suitable for making cooking utensils.

Question 14.
A light ray enters from medium A to medium B as shown in the figure. The refractive index of medium B relative to A will be

(a) greater than unity
(b) less than unity
(c) equal to unity
(d) zero
Answer:
(a) greater than unity
Since the light rays in medium 6 go towards normal, So, it has a greater refractive index and lesser velocity of light w.r.t. medium A. Hence, the refractive index of medium B w.r.t. medium A is greater than unity.

Question 15.
The height of a plant is regulated by:
(a) DNA which is directly influenced by growth hormones.
(b) Genes that regulate the proteins directly.
(c) Growth hormones under the influence of the enzymes coded by a gene.
(d) Growth hormones directly under the influence of a gene.
Answer:
(c) Growth hormones under the influence of the enzymes coded by a gene.
Explanation: The height of a plant is regulated by a complex interplay of genetic factors, growth hormones, and enzyme activity.

Genes play a crucial role in determining the production and activity of growth hormones in plants. Specific genes code for enzymes that are involved in the synthesis, metabolism, and signaling pathways of growth hormones. These enzymes control the production, transportation, and breakdown of growth hormones within the plant.

While DNA carries the genetic information that influences the production of growth hormones, it is not directly influenced by growth hormones itself (option a). Genes regulate the production of proteins, including the enzymes involved in growth hormone metabolism, rather than directly regulating the proteins themselves (option b). Option d suggests that growth hormones act directly under the influence of a gene, but it is the enzymes coded by genes that mediate the effects of growth hormones.

Question 16.
What do you understand by phenotype?
(a) External appearance of an organism
(b) Genetic makeup of an organism
(c) Both (a) and (b)
(d) None of the above
Answer:
(a) External appearance of an organism

Questions 17 to 20 consist of two statements – Assertion (A) and Reason (R). Answer these questions by selecting the appropriate option given below:

(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true and R is not the correct explanation of A.
(c) A is true but R is false.
(d) A is false but R is true.

Question 17.
Assertion: Diabetes mellitus is caused due to lack of insulin in the body.
Reason: Insulin helps in utilisation of glucose in the body.
Answer:
(a) Both A and R are true and R is the correct explanation of A.
Explanation: Insulin is a hormone released by the p-cells of the pancreas. It maintains the blood glucose level in the body, by its proper utilisation. So, lack of insulin causes accumulation of glucose in the blood and hence a disease called diabetes mellitus is caused.

Question 18.
Assertion (A): Urethra in the human male acts as a urinogenital canal.
Reason (R): The Urethra carries only urine, while sperms are carried by the vas deferens only.
Answer:
(c) A is true, but R is false.
R can be corrected as The urethra is the tube that allows urine to pass out of the body. In human males, it is a long tube that runs through the penis. It also carries semen in human males and is the common passage for both urine and sperm.

Question 19.
Assertion: Lumen of the fallopian tube is lined by ciliated epithelium.
Reason: Ciliated epithelium helps to move the zygote towards the uterus for implantation.
Answer:
(a) Both A and R are true and R is the correct explanation of A
Explanation: Lumen of the Fallopian tube is lined by ciliated epithelium as cilia have a rhythmic I waving and beating motion that helps substances to travel from one place to another.

Question 20.
Assertion (A): The blue colour of the sky appears due to the scattering of the blue colour.
Reason (R): Blue colour has the shortest wavelength in the visible spectrum.
Answer:
(a) Both (A) and (R) are true, but (R) is the correct explanation of (A).
During the daytime, the sky appears blue. This is because the size of the particles in the atmosphere is smaller than the wavelengths of visible light. So, they scatter the light of shorter wavelengths. The scattered blue light enters our eye, according to Rayleigh’s scattering.

Section – B

Questions No. 21 to 26 are very short answer questions.

Question 21.
Write the essential functions performed by ozone in the upper layer of Earth’s atmosphere. How is it produced? Name the synthetic chemicals mainly responsible for the drop in the amount of ozone in the atmosphere. How can the use of these chemicals be reduced?
Answer:
The ozone layer absorbs most of the harmful ultraviolet radiation from the sun to the earth. It is formed high up in the atmosphere by the action of ultraviolet radiation on oxygen gas. Chlorofluorocarbons are the synthetic chemicals responsible for the drop in the amount of ozone in the atmosphere.

The use of these chemicals can be reduced by:
1. Replacement of chlorofluorocarbons with hydrochlorofluorocarbons because they break down more quickly.
2. Safe disposal of old appliances such as refrigerators and freezers.

Question 22.
State any two practices, which can help in the protection of our environment.
Answer:
Two practices which can help in the protection of our environment are
(a) Disposable of the waste after its separation as biodegradable and non-biodegradable. (1)
(b) Judicious use of unleaded petrol and alternate sources of energy, e.g. solar energy, wind energy, hydro energy. (1)

Question 23.
Draw a diagram of the human excretory system and label the following terms given below. Aorta, Vena cava, Urinary bladder, and Urethra.
OR
List two vital functions of the kidneys.
Answer:

Two vital functions of kidneys are:
(1) They help in the removal of waste products that are harmful to the body. It is called excretion.
(2) They maintain the proper level of salt and water concentration in the body. It is called osmoregulation.

Question 24.
Six wires labelled as A, B, C, D, E, and F have been designed as per the following parameters.

Wire	Length	Diameter	Material	Resistance
A	L	2d	Aluminium	R1
B	2l	d/2	Constantan	R2
C	3l	d/2	Constantan	R3
D	l/2	3d	Copper	R4
E	2l	2d	Aluminium	R5
F	l/2	4d	Copper	R6

Answer the following questions using the above data.
(a) Which of the wires has maximum resistance and why?
(b) Which of the wires has minimum resistance and why?
Answer:
(a) The wire C has maximum resistance because it has maximum length, least thickness, and highest resistivity. (1)
(b) The wire F has the minimum resistance since it has the least length, maximum thickness, and least resistivity. [using, R = ρ\(\frac{l}{A}\)] (1)

Question 25.
Guinea pig having black colour when crossed with guinea pig having the same colour produced 80 offspring, out of which 60 were black and 20 were white. Now find out:
(i) What is the possible genotype of the guinea pigs?
(ii) Which trait is dominant and which trait is recessive?
(iii) What is this cross called as and what is its phenotypic ratio?
OR
Why do all the gametes formed in the human females have an X chromosome?
Answer:
(i) The possible genotype of the guinea pigs is Bb x Bb.
(ii) Black colour is dominant and white colour is recessive.
(iii) This is an example of a monohybrid cross and its phenotypic ratio is 3 : 1.
OR
The sex chromosome in human female is homomorphic i.e., they contain the same chromosome XX. During meiosis process at the time of gamete formation all egg cells will get one copy of X chromosome, hence all the gametes formed in human females have an X chromosome.

Question 26.
(a) State the role of ATP in cellular respiration.
(b) What ensures sufficient exchange of gases in plants?
Answer:
(a) ATP is considered as energy of a cell. It is used as a fuel in various cellular activities such as the contraction of muscles, contractions of nerve impulses, protein synthesis, etc.
(b) Stomata and large intercellular spaces present throughout the plant body ensure the sufficient exchange of gases in the plant. (2)

Section – C

Questions No. 27 to 33 are short answer questions.

Question 27.
B₁, B₂ and B₃ are three identical bulbs connected, as shown in the figure. Ammeters A₁, A₂ and A₃ are connected as shown. When all the bulbs glow, the current of 3 A is recorded by ammeter A.

(i) What happens to the glow of the other two bulbs when bulb B₁ gets fused?
(ii) What happens to the reading of A₁, A₂, A₃ and A when the bulb B₂ gets fused?
(iii) How much power is dissipated in the circuit when all the bulbs glow together?
Answer:
Resistance of combination of three bulbs in parallel,
R_eq = \(\frac{V}{I}=\frac{4.5}{3}\) = 1.5Ω
If R is the resistance of each wire, then
\(\frac{1}{\mathrm{R}_{\mathrm{eq}}}=\frac{1}{\mathrm{R}}+\frac{1}{\mathrm{R}}+\frac{1}{\mathrm{R}}\)
⇒ \(\frac{1}{\mathrm{R}_{\mathrm{eq}}}=\frac{3}{\mathrm{R}}\)
⇒ R = 3R_eq
⇒ R = 3 × 1.5 = 4.5Ω
Current in each bulb, I = \(\frac{\mathrm{V}}{\mathrm{R}}=\frac{4.5 \mathrm{~V}}{4.5 \Omega}\) = 1A
(i) When bulb B₁ gets fused, the currents in B₂ and B₃ remain same I₂ = I₃ = 1A, as the voltage across them remains the same so, their glow remains unaffected.

(ii) When bulb B₂ gets fused, the current in B₂ becomes zero and currents in B₁ and B₃ remains 1 A.
Total current I = I₁ + I₂ + I₃
= 1 + 0 + 1 = 2A
Current in ammeter A₁ = 1 A
Current in ammeter A₂ = 0
Current in ammeter A₃ = 1 A
Current in ammeter A = 2 A

(iii) When all the bulbs are connected in the circuit:
Power dissipated, P = \(\frac{\mathrm{V}^2}{\mathrm{R}_{\mathrm{eq}}}\)
⇒ P = \(\frac{(4.5)^2}{1.5}\) = 13.5 W

Question 28.
The diagram shown below is of the electrolytic refining of copper.

In this process, a thick block of impure metal is used as an anode, and a thin strip of pure metal is used as a cathode. A solution of metal is used as an electrolyte.
(a) What happens when an electric current is passed in the given system?
(b) Draw your conclusion from the given figure.
(c) Illustrate the reaction of the process with the help of a chemical equation.
Answer:
(a) When an electric current is passed, copper ions from the electrolyte are reduced as copper which gets deposited on the cathode. (1)
(b) An equivalent amount of pure copper from the anode gets oxidized to copper ion and goes into the solution and from there, it goes to the cathode and gets deposited. (1)
(c) The reactions that take place during the refining of copper are as follows: (1)
At cathode, Cu²⁺ (aq) + 2e^– → Cu(s)
At anode, Cu(s) → Cu²⁺ (aq) + 2e^–
This cycle is repeated until the whole of the copper ion from the impure block is dissolved and deposited on the cathode.

Question 29.
(i) Define activity series of metals. Arrange the metals gold, copper, iron, and magnesium in order of their increasing reactivity.
(ii) What will you observe when:
(a) Some zinc pieces are put in a copper sulphate solution.
(b) Some silver pieces are put into a green coloured ferrous sulphate solution.
Answer:
(i) The series of metals in which metals are arranged in decreasing order of their reactivity is called activity series of metals. The increasing order of reactivity will be:
Au < Cu < Fe < Mg.

(ii) (a) When zinc pieces are put into blue colour copper sulphate solution. Zinc displaces copper from copper sulphate solution. In this process, blue copper sulphur solution turns into colourless.

(b) When some silver pieces are put into green coloured ferrous sulphate solution, there will be no reaction because Ag is less reactive than iron.
Ag(s) + FeSO₄(aq) → No reaction
The reaction will not take place because Ag is less reactive than iron.

Question 30.
Ram wants to know about a device that works based on a current-carrying conductor placed in a magnetic field.
(a) What conclusion do you get from the observation that a current-carrying wire deflects a compass needle placed near it? Name the device that works on that principle.
(b) Write uses of galvanometer.
(c) When the force is experienced by a current-carrying conductor placed in a magnetic field largest?
Answer:
(a) The conclusion that can be drawn a magnetic field exists around a current-carrying conductor. Based on this principle, if a current-carrying conductor is placed in a uniform magnetic field, then a force is exerted on that conductor. Galvanometer works on this principle. (1)
(b) A galvanometer is used to detect very small currents or deflection of charges. Special purpose galvanometer can measure charges upto a few nano coulombs. It can also be used to measure current and potential differences by biasing with a resistor. (1)
(c) The force experienced by a current-carrying conductor placed in a magnetic field is the largest when the conductor is kept perpendicular to the direction of the magnetic field. (1)

Question 31.
Define:
(i) Food chain
(ii) Food web
(iii) Biological magnification.
Answer:
(i) Food chain: The series of organisms taking part at various trophic levels for the flow of energy is called a food chain.

(ii) Food web: The food web represents many interlinked food chains as each organism is generally eaten by two or more other kinds of organisms. It cannot be represented by a straight line.

(iii) Biological magnification: The accumulation of harmful chemicals at each trophic level with the help of various biotic and abiotic factors is called biological magnification.

Question 32.
(i) Define the term alloy and amalgam. Name the alloy used for welding electric wires together. What are its constituents?
(ii) Name the constituents of the following alloys:
(a) Brass
(b) Stainless steel
(c) Bronze
Answer:
(i) An alloy is a homogeneous mixture of a metal with a metal or a non-metal. Amalgam is an alloy of a metal with mercury.
The alloy used for welding electric wires together is Solder. Its constituents are lead and Tin.

(ii) (a) Brass: Brass alloy is made of zinc (Zn) and copper (Cu).
(b) Stainless steel: It contains chromium (12.14%), molybdenum (0.21 %), nickel (less than 2%), and carbon (about 0.11%).
(c) Bronze: It is an alloy consisting primarily of copper, commonly with about 12% tin and often with the addition of other metals (such as aluminium, manganese, nickel, or zinc) and sometimes non-metals or metalloids such as arsenic, phosphorus or silicon.

Question 33.
State one characteristic of each of the chemical reactions which takes place when:
(i) Dilute hydrochloric acid is added to sodium carbonate.
(ii) Lemon juice is added gradually to the potassium permanganate solution.
(iii) Dilute sulphuric acid is added to the barium chloride solution.
Answer:
(i) Carbon dioxide gas is released.
(ii) Colour changes from purple to colourless
(iii) White precipitate of barium sulphate is formed

Section – D

Questions No. 34 to 36 are long answer questions.

Question 34.
A compound X is formed by the reaction of a carboxylic acid C₂H₄O₂ and an alcohol in the presence of a few drops of H₂SO₄. The alcohol on oxidation with alk.KMnO₄ followed by acidification gives the same carboxylic acid as used in this reaction. Give the names and structures of carboxylic acid, alcohol, and the compound X. Also write the reaction.
Or
(a) A teacher of a school instructed the students to carry out the following reactions and also told them to write the reactions involved when ethanol is heated with alkaline potassium permanganate, ethanoic acid with sulphuric acid, and sodium respectively.
(b) What happens when barium chloride solution is mixed with copper sulphate solution?
Answer:
Carboxylic acid having molecular formula C₂H₄O₂ is acetic acid or ethanoic acid. Its structure is (1)

Since, an alcohol which on oxidation with alk. KMnO₄ followed by acidification gives ethanoic acid. Therefore, it must be ethanol. Its structure is CH₃-CH₂-OH.

Since compound X is formed by the reaction of ethanoic acid with ethanol in the presence of a few drops of cone, H₂SO₄. Therefore, compound X must be an ester, i.e. ethyl ethanoate. Its structure is


(b) When barium chloride solution is mixed with copper sulphate solution a white precipitate is obtained. The reaction involved is as follows:
BaCl₂ (aq) + CuSO₄ (aq) → BaSO₄ (s) + CuCl₂ (aq) (2)

Question 35.
(i) Observe the given figure and answer the following:

(a) Identify the gas evolved.
(b) How will you test the presence of gas evolved?
(c) What is the nature of the gas evolved?
(d) What will happen to the lime water when the gas evolved is passed through it? Give chemical equation.
(e) What happens to the lime water when this gas is passed for a longer period?

(ii) Account for the following:
(a) State the relation between the hydrogen ion concentration of an aqueous solution and its pH.
(b) An aqueous solution has a pH value of 7.0. Is this solution acidic, basic or neutral?
(c) Which has a higher pH, 1 M HCl or 1 M NaOH solution?
(d) Tooth enamel is one of the hardest substances in our body. How does it undergo damage due to eating chocolates and sweets? What should we do to prevent it?
(e) How do H⁺ ions exist in water?
OR
Answer the following questions:
(i) What colour will be produced when we put a drop of distilled water on pH paper? What is the pH of distilled water?
(ii) The pH of a solution is less than 7. What does it indicate? What is the pH of 1 M HCl solution?
(iii) What is the pH of solution A’ which liberates CO₂ gas with a carbonate salt? Give the reason.
(iv) What is the pH of solution ‘B’ which liberates NH₃ gas with an ammonium salt? Give reason.
(v) How do you increase or decrease the pH of pure water?
Answer:
(i) (a) Carbon dioxide gas is evolved.
(b) Carbon dioxide gas is a non-supporter of combustion so when a burning splinter is brought near this gas, it gets extinguished.
(c) This gas is acidic as it turns blue litmus red.
(d) Lime water will turn milky.
Ca(OH)₂ + CO₂ → CaCO₃ + H₂O
(e) When this gas is passed through lime water for a longer period, the milky lime water disappears.
CO₂ + CaCO₃ + H₂O → Ca(HCO₃)₂

(ii) (a) Hydrogen ion concentration of an aqueous solution is inversely proportional to its pH.
(b) The solution is neutral.
(c) 1 M NaOH solution has higher pH because bases have higher pH values than acids.
(d) Tooth enamel gets corroded slowly when pH in the mouth is below 5.5. Acid is produced in mouth due to the degradation of food which is partially hydrolysed by saliva. But if excess acid is produced, it causes tooth decay. It can be prevented by using tooth paste which is generally basic.

(e) H⁺ ions exist in water as H₃O⁺ ions.
OR
(i) The colour produced will be green. Its pH is 7.
(ii) It indicates that the solution is acidic. The pH of 1M HCL is zero.
(iii) The pH of solution ‘A’ is lesser than 7. Carbonate salts react with acids (A) to liberate CO₂ gas.
(iv) The pH of solution ‘B’ is lesser than 7 because ‘B’ is an alkali as it liberates NH₃ gas.
(v) By adding few drops of alkali to pure water, it’s pH increases; and by adding a few drops of an acid decreases the pH of pure water.

Question 36.

The diagram above shows an electric circuit in which resistances R₁, R₂, R₃, R₄, and R₅ are connected. There is some air gap at the joint of wires.
(a) What is the resistance of an air gap?
(b) Derive an expression for equivalent resistance for the circuit.
(c) If the wire of resistance R₁ and resistivity ρ is stretched to double its length, how will its resistance and resistivity be affected?
Or
Study the following circuit and answer the questions that follow:

(a) State the type of combination of two resistors in the circuit.
(b) How much current is flowing through 10 Ω and 15 Ω resistors?
(c) What is the ammeter reading?
Answer:
(a) The resistance of an air gap is very large almost infinite. Since there is no contact between the conducting wires. (1)
(b) R₂ and R₃ are in series. Thus, for this combination, R’ = R₂ + R₃
Similarly, R₄ and R₅ are in series, so R” = R₄ + R₅.
R’ and R” are in parallel, then

(c) Let the initial length of wire be l and the area of cross-section is A.
When the wire is stretched to double its length, the final length is l₂ = 2l₁
But the volume of the wire remains the same.

∴ Resistance is increased by 4 times.
Resistivity remains constant, as it is the property of the material and does not depend on the dimensions of the material. (2)
Or
(a) Two resistors are in parallel combination. (1)
(b) Current through
10 Ω resistor, I₁ = \(\frac{V}{R}=\frac{3}{10}\) = 0.3A
15 Ω resistor, I₂ = \(\frac{V}{R}=\frac{3}{15}\) = 0.2A (2)
(c) Ammeter reading = Total current flowing through the circuit = 0.3 + 0.2 = 0.5A (2)

Section – E

Questions No. 37 to 39 are case-based/data-based questions with 2 to 3 short sub-parts. Internal choice is provided in one of these sub-parts.

Question 37.
Mass can neither be created nor destroyed in a chemical reaction. That is, the total mass of the elements present in the products of a chemical reaction has to be equal to the total mass of the elements present in the reactants. In other words, the number of atoms of each element remains the same, before and after a chemical reaction. Hence, we need to balance a skeletal chemical equation.

To make a chemical equation more informative, the physical states of the reactants and products are mentioned along with their chemical formulae. The gaseous, liquid, aqueous and solid states of reactants and products are represented by the notations (g), (l), (aq) and (s), respectively. Aqueous (aq) is written if the reactant or product is present as a solution in water.

Usually, physical states are not included in a chemical equation unless it is necessary to specify them. Sometimes the reaction conditions, such as temperature, pressure, catalyst, etc., for the reaction are indicated above and/or below the arrow in the equation. For example,

(a) Balance the chemical equation for a given reaction with the proper physical state.
Fe + H₂O → Fe₃O₄ + H₂
(b) Which law is demonstrated above?
OR
Write a balanced chemical equation for the reaction of Barium chloride and Aluminium sulphate to give Barium sulphate and aluminium chloride.
Answer:
(a) The balanced chemical equation for a given reaction is;
3Fe(s) + 4H₂O(g) → Fe₃O₄(s) + 4H₂(g)

(b) Law of Conservation of Mass is demonstrated in the above equation.
OR

Question 38.
Mr. Sharma was suffering from health issues. He went for thorough health check-ups and was diagnosed to be HIV positive. Soon, this news spread in his neighborhood, and on account of this, he faced social isolation.
Answer the following questions based on the information given above.
(a) Do you think people’s indifference towards HIV-positive people is justifiable? What kind of approach should we have towards the person suffering?
(b) How can one protect oneself from this disease?
(c) What values are not promoted by Mr. Sharma’s neighbours?
Or
Write down the modes of transmission of HIV.
Answer:
(a) not, we should exhibit human approach/behaviour and should not treat them as isolated. (1)
(b) One should be aware of the mode of transmission of disease, danger of sharing needles, transfusion of contaminated blood, etc. (1)
(c) Sympathy for fellow human beings ‘care’ and humane nature values are not promoted by Mr. Sharma’s neighbours. (2)
Or
Modes of transmission of HIV are discussed below:
(a) Unprotected sexual interaction with a previously infected person.
(b) Reusing needles used by infected individuals. (2)

Question 39.
The given table shows that the resistivity of an alloy is generally higher than that of its constituent metals. Alloys do not oxidize (bum) readily at high temperatures. For this reason, they are commonly used in electrical heating devices, like electric iron, toasters etc. Tungsten is used almost exclusively for filaments of electric bulbs, whereas copper and aluminum are generally used for electrical transmission lines.

(a) How much current will an electric bulb draw from a 200 V source, if the resistance of the bulb filament is 1500 Ω?
(b) Why are alloys used in heating devices?
(c) Which alloy is used exclusively for filaments of electric bulbs?
OR
(d) Write the composition of Nichrome.
Answer:
(a) Given that V = 200V; R = 1500 Ω.
Therefore, current I = 200 V/1500 Ω = 0.13 A.
(b) Alloys do not oxidise (bum) readily at high temperatures. For this reason, they are commonly used in electrical heating devices, like electric iron, toasters etc.
(c) Tungsten
OR
(d) Nichrome is an alloy of Ni, Cr, Mn, and Fe.