Students must start practicing the questions from CBSE Sample Papers for Class 10 Science with Solutions Set 5 are designed as per the revised syllabus.
CBSE Sample Papers for Class 10 Science Set 5 with Solutions
Time: 3 Hours
Maximum Marks: 80
General Instructions:
- This question paper consists of 39 questions in 5 sections.
- All questions are compulsory. However, an internal choice is provided in some questions. A student is expected to attempt only one of these questions.
- Section A consists of 20 objective type questions carrying 1 mark each.
- 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.
- 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.
- 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.
- 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 not a characteristic of a rear view mirror on a car?
(a) Convex in nature
(b) Concave in nature
(c) They have wider field of coverage
(d) They give a virtual image
Answer:
(b) Concave in nature
Explanation: As rear view mirror is a concave mirror. It has wider field of coverage and gives a 1 virtual, erect and diminished image of an object.
Question 2.
Metals are refined by using different methods. Which of the following metals are refined by electrolytic refining?
(a) Au
(b) Ca
(c) Na
(d) K
Answer:
(a) Au
Electrolytic refining is used for metals like Cu, Zn, Ag, Au, etc. The method to be used for refining an impure metal depends on the nature of the metal as well as on the nature of impurities present in it.
Question 3.
In the given diagram, How does the rectangular loop carrying a current i, behave when placed near a long straight wire that is parallel to one side of the loop and lies in the same plane as the loop?
(a) Rotate about an axis parallel to the wire
(b) Move towards the wire
(c) Move away from the wire or towards right
(d) Remains stationary
Answer:
(b) Move towards the wire
Explanation:
Question 4.
A student performed the following four experiments,
Which of the following observations is correct?
(a) The displacement reaction occurs in all experiments except III.
(b) The solid deposition is observed in the I, II, and III experiments.
(c) The solid deposition is observed in the I and II experiments.
(d) The displacement reaction is observed in the IV experiment.
Answer:
(b) The solid deposition is observed in the I, II, and III experiments.
In I, II, and III experiments, he found the formation of a solid deposition because Al, Zn, and Fe are more reactive than Cu. They will replace Cu from its sulphate solution and Cu will deposit as solid.
Question 5.
Which of the following is used for the dissolution of gold?
(a) Hydrochloric acid
(b) Sulphuric acid
(c) Nitric acid
(d) Aqua regia
Answer:
(d) Aqua regia
Explanation: Aqua regia is a mixture of hydrochloric acid and nitric acid in a ratio 3 : 1 and it can dissolve noble metals such as gold, palladium, and platinum, which, however are not soluble in either of the acids alone.
Question 6.
Which of the following represents the correct balanced chemical equation?
(a) AlCl3 + NH4OH → Al(OH)3 + NH4Cl
(b) AlCl3 + 3NH4OH → Al(OH)3 + 3NH4Cl
(c) 2AlCl3 + 3NH4OH → 2Al(OH)3 + 2NH4Cl
(d) 3AlCl3 + 4NH4OH → Al(OH)3 + NH4Cl
Answer:
(b) AlCl3 + 3NH4OH → Al(OH)3 + 3NH4Cl
Chemical equation (b) is a balanced one. The balanced chemical equation is one in which the total number of atoms of each element is equal on both sides of the equation.
Question 7.
Offspring formed by the asexual method of reproduction have greater similarity among themselves because:
(i) Asexual reproduction involves only one parent.
(ii) Asexual reproduction does not involve gametes.
(iii) Asexual reproduction occurs before sexual reproduction.
(iv) Asexual reproduction occurs after sexual reproduction.
(a) (i) and (ii)
(b) (i) and (iii)
(c) (ii) and (iv)
(d) (iii) and (iv)
Answer:
(a) (i) and (ii)
Explanation: Offspring have greater similarity as only one parent is involved in asexual reproduction thus no gametes are formed. The basis of asexual reproduction is mitosis (division of a nucleus into two identical daughter nuclei). Each daughter nucleus has the same genetic makeup because of the replication of parental DNA. The new offspring produced are called clones.
Question 8.
Consider the following figure that represents the food web.
Which of the following options depicts the primary consumer in the food web?
(a) Rabbits and Mice
(b) Foxes and Grass
(c) Rabbits and Fleas
(d) Seeds and Foxes
Answer:
(a) Rabbits and Mice
The primary consumers are the organisms who directly feed on the producers. In the given food web, rabbits and mice are the primary consumers.
Question 9.
What is the colour of the ash formed when a magnesium ribbon is burnt in the air?
(a) White
(b) Black
(c) Yellow
(d) Pink
Answer:
(a) White
Explanation: When the magnesium ribbon is burned in the air, it bums with the white dazzling I flame leading to the formation of the white colour ash, which is magnesium oxide.
Question 10.
The result of a dihybrid cross between two individuals is recorded in the table as
Phenotypes of progeny | Number of seeds obtained |
Round, A | 315 |
Round, B | 108 |
Yellow, C | 101 |
Wrinkled, D | 32 |
Choose the correct option for A, B, C, and D.
Answer:
(b) A – Yellow, B – Green, C – Wrinkled, D – Green
The dihybrid cross between the round, green plant, and the wrinkled, yellow plant is shown as
Question 11.
In which of the following groups of organisms, the food material is broken down outside the body and absorbed?
(a) Mushroom, green plants, amoeba
(b) Yeast, mushroom, bread mould
(c) Paramecium, amoeba, cuscuta
(d) Cuscuta, lice, tapeworm
Answer:
(b) Yeast, mushroom, bread mould
Explanation: Yeast, mushrooms, and bread mould all exhibit a saprophytic mode of nutrition. They use digestive enzymes secreted outside their body to break down complex organic substances and absorb basic molecules as nutrition.
Question 12.
Which of the following is not a functional component of an ecosystem?
(a) Ecological pyramids
(b) Decomposers
(c) Sunlight
(d) Energy flow
Answer:
(a) Ecological pyramids
Ecological pyramids are not a functional component of an ecosystem.
Question 13.
A cylindrical conductor of length T and uniform area of cross-section ‘A’ has resistance ‘R’. The area of the cross-section of another conductor of the same material and the same resistance but of length ‘2l’ is :
(a) 0.5 A
(b) 1.5 A
(c) 2 A
(d) 3 A
Answer:
(c) 2 A
Explanation: A cylindrical conductor of length ‘l’ and uniform area of cross-section ‘A’ has resistance ‘R’. The area of cross-section of another conductor of same material and same resistance but of length ‘2l’ will be 2 A. This can be explained as:
Question 14.
Which of the following can make a parallel beam of light when light from a point source is incident on it?
(a) Concave mirror as well as convex lens
(b) Convex mirror as well as concave lens
(c) Two plane mirrors placed at 90° to each other
(d) Concave mirror as well as concave lens
Answer:
(a) Concave mirror as well as convex lens
Both convex lenses and concave mirrors can make a parallel beam of light when light from a point source is incident on it.
Question 15.
The figure given below shows the magnetic field produced by a currents carrying wire. Which of the following diagrams shows it correctly?
Answer:
Explanation: When current flows through and current-carrying wire, the direction of the magnetic I field is calculated by right-hand thumb rule.
Question 16.
The law of dominance states that
(a) a dominant trait always suppresses the recessive trait.
(b) the recessive trait is always expressed.
(c) the dominant trait is always suppressed.
(d) the recessive trait dominates over the dominant trait.
Answer:
(a) a dominant trait always suppresses the recessive trait.
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: When a current-carrying rod is suspended between a U-shaped magnet, and the rod deflects. Reason: A force is exerted on the rod due to the magnetic field.
Answer:
(a) Both A and R are true and R is the correct explanation of A.
Explanation: A force is always exerted due to a magnetic field in the same way electric current flowing I through any conductor produces a magnetic field. In this case, Fleming’s left-hand rule is used to I predict the directions of the magnetic field, current, and displacement.
Question 18.
Assertion (A): Positive phototropism means movement towards light.
Reason (R): When sunlight falls on one side of the plant, the auxin diffuses towards the sunny side of the shoot. Auxin concentration stimulates cells to grow longer and the stem appears bending towards sunlight.
Answer:
(c) A is true, but R is false.
It can be corrected as When sunlight falls on one side of the plant, the auxin diffuses towards the shady side of the shoot.
Question 19.
Assertion: Sometimes, the eye may gradually lose its power of accommodation.
Reason: The crystalline lens of people at old age becomes milky and cloudy.
Answer:
(b) Both A and R are true and R is not the correct explanation of A.
Explanation: The person cannot see the objects distinctly and comfortably because of accommodation. The vision becomes blurred due to the refractive defects of the eye.
Question 20.
Assertion (A): The stars twinkle while the planet does not.
Reason (R): The stars are much bigger than the planets.
Answer:
(b) Both A and R are true but R is not the correct explanation of A.
As planets are much closer to the Earth than stars, planets can be considered as a collection of a large number of point-sized sources of light. The total variation in the amount of light entering our eye from all their point-sized sources will average out to zero which nullifies the twinkling effect of each other. Therefore, planets do not twinkle.
Section – B
Questions No. 21 to 26 are very short answer questions.
Question 21.
The refractive indices of kerosene, turpentine and water are 1.44,1.47 and 1.33, respectively. In which of these materials does light travel the fastest?
OR
Why does a ray of light passing through the centre of curvature of a concave mirror gets reflected among the same path after reflection?
Answer:
We know that,
Refractive index = \(\frac{\text { Speed of light in air }}{\text { Speed of light in medium }}\)
So, the speed of light m medium = \(\frac{\text { Speed of light in air }}{\text { Refractive index }}\)
It is obvious from the above relation that the speed of light will be the maximum in that medium which has the lowest refractive index. Now, out of kerosene, turpentine, and water, water has the lowest re¬fractive index of 1.33. So, the light will have a maximum speed in the water.
OR
The ray of light passing through the centre of curvature of a concave mirror gets reflected along the same path after a reflection because the angle of incidence is 0°. That is the ray passing through the centre of curvature is incident normally to the mirror. The angle of reflection should also be 0°.
Question 22.
In a pea plant, find the contrasting trait if the flower is white and the shape of the pod is constricted.
Answer:
Contrasting traits of pea plants were used by Mendel and were classified as dominant or recessive.
Characters | Given traits | Contrasting traits |
(a) Colour of flower | White | Violet |
(b) Shape of the pod | Constricted | Full |
Question 23.
Given below is a reaction which occurs in the stratosphere.
O2 \(\rightleftharpoons\) O2 + [O]
(i) Name the two reactions which are in equilibrium thereby maintaining the steady concentration of ozone in the ozonosphere.
(ii) What is being absorbed by the ozone for the occurrence of the above two reactions?
Answer:
(i) Photo-dissociation of ozone and generation of ozone are the two reactions that are in equilibrium thereby maintaining a steady concentration of ozone in the ozonosphere.
(ii) Ultraviolet radiations from the sun are being absorbed by the ozone for the occurrence of given two reactions
Question 24.
The given data shows the focal lengths of three concave mirrors A, B, and C, and the respective distances of different objects from these mirrors.
Concave mirrors | Object distances (in cm) | Focal length (in cm) |
A | 45 | 20 |
B | 30 | 15 |
C | 20 | 30 |
In the given positions of objects from the mirrors, which of them will form diminished images of the object?
Answer:
Mirror A will form a diminished image of the object. Because the object is very far from the mirror. [More than twice it’s focal length 2f = 2 × 20 = 40)] (2)
Question 25.
List two different functions performed by the pancreas in our body.
Answer:
Different functions performed by the pancreas in our body are:
- Pancreas makes two hormones i.e., insulin and glycogen that regulate blood sugar levels.
- It secretes pancreatic juice that aids in the digestion of food.
Question 26.
(a) Give a reason, why the ozone layer in the stratosphere is considered useful. What destructive effect do chlorofluorocarbons bring about in the atmosphere?
(b) Explain why, it is better to use paper bags than plastic bags.
Answer:
(a) The ozone layer is very important for the existence of life on Earth because it prevents harmful ultraviolet (UV) radiations coming from the sun from reaching the Earth. CFCs deplete ozone, resulting in increasing the passage of harmful UV radiation to the earth. (1)
(b) It is better to use paper bags than plastic bags because
- Paper is recyclable whereas plastic bags can not be recycled.
- Plastic cannot be degraded and products made up of plastic pollute the environment, whereas paper is biodegradable and does not cause pollution.
- Moreover, even on burning, the paper will not cause much pollution but plastic on burning will release toxic chemicals into the environment thus, polluting the environment. (Any two) (1)
Section – C
Questions No. 27 to 33 are short answer questions.
Question 27.
How do Mendel’s experiments show that traits are inherited independently?
Answer:
When Mendel crossed pure pea plants with round, yellow seeds with pure plants with wrinkled, green seeds in F1 generation all pea plants with round and yellow seeds were produced. This shows that round and yellow are dominant characters whereas green and wrinkled are recessive characters. Again, when these F1 plants were crossed round, yellow pea plants, as well as green, wrinkled seeds pea plants were produced. But in addition to these two new characters were produced i.e., round and green, wrinkled and yellow seeds pea plants were produced.
This shows that two pair of characters combines in the F2 generation, but they get separated and behave independently in F2 generation.
Round-yellow, round-green, wrinkled-yellow, wrinkled-green – 9 : 3 : 3 : 1
Question 28.
The pH of a salt used to make tasty and crispy pakoras is 14.
(a) Examine the salt used.
(b) Write a chemical equation for its formation.
(c) List its two uses.
Answer:
The pH of a salt used to make tasty and crispy pakoras is 14.
(a) The salt is sodium hydrogen carbonate. Its formula is NaHCO3. This is also known as baking soda. (1)
(b) The chemical reaction involved as
(c) Uses:
(i) For making baking powder.
(ii) Also used as an ingredient in antacids. (1)
Question 29.
Give reasons for the following:
(i) Platinum, gold, and silver are used to make jewellery.
(ii) Sodium, potassium, and lithium are stored under oil.
(iii) Aluminium is a highly reactive metal, yet it is used to make utensils for cooking.
Answer:
(i) The reactivity of metals is important in jewelry making. It should be non-reactive to avoid tarnish on the metal. Because electronegativity and nonmetallic character grow from left to right in the periodic table, the oxidizing power of elements increases. Gold, silver, and platinum are hence poor oxidizing agents.
They are very lustrous, corrosion-resistant metals. They have strong durability. They may be molded into any shape or pattern due to their extreme malleability and ductility.
Therefore, Platinum, Gold, and Silver are used to make jewelry.
(ii) Sodium, potassium, and lithium are stored in kerosene because they are very reactive metals and react very vigorously with air as well as water. They are kept immersed in kerosene oil to prevent their contact with air and moisture.
(iii) Aluminium is a highly reactive metal, but it is resistant to corrosion. The reason for this is that aluminium reacts with oxygen present in the air to form a thin layer of aluminium oxide. This oxide layer is very stable and prevents further reaction of aluminium with oxygen. It is light in weight and a good conductor of heat. Therefore, it is used to make utensils for cooking.
Question 30.
Shyam wants to have twice in size of a real image of an object placed at 25 cm from a convex lens.
(a) Specify the distance of the image from the lens.
(b) Find the focal length of the lens.
(c) Find the power of the convex lens.
Answer:
Question 31.
Explain how the following metals are obtained from their compounds by reduction process:
(i) Metal X which is lower in reactivity series.
(ii) Metal Y which is in middle of the reactivity series.
(iii) Metal Z which is high in the reactivity series.
OR
When metal P is treated with a dilute acid Q, then a gas G is evolved which burns readily by making a little explosion.
(i) Name any two metals which can behave like metal P.
(ii) Name any two acids which can behave like acid Q.
(iii) Name the gas G.
(iv) Is the gas G lighter than or heavier than air?
(v) Is the reaction between metal P and dilute acid Q exothermic or endothermic?
Answer:
(i) Metals low in reactivity series are obtained by the method of heating their oxides with carbon.
(ii) Y is in the middle of the series, it can be obtained by heating with a reducing agent like carbon or highly reactive metals like Na, Ca and Al.
(iii) Metal Z is high up in the reactivity series. It can be obtained by electrolytic reduction.
OR
(i) Zinc and Iron.
(ii) Dilute hydrochloric acid and dilute sulphuric acid.
(iii) Hydrogen
(iv) Lighter than air
(v) Exothermic
Question 32.
Rishi went to a palmist to show his palm. The palmist used a special lens for this purpose.
(a) Where should the palmist place/hold the lens to have a real and magnified image of an object?
(b) If the focal length of this lens is 10 cm and the lens is held at a distance of 5 cm from the palm, use the lens formula to find the position and size of the image.
Answer:
(a) A palmist uses a convex lens to see the magnified image of palm lines. The palmist will hold the lens where the palm is in between the focus and pole of the lens. (1)
(b) Given, focal length f = 10 cm and object distance, u = -5 cm
From lens formula, \(\frac{1}{v}-\frac{1}{u}=\frac{1}{f}\)
⇒ \(\frac{1}{v}=\frac{1}{10}+\frac{1}{-5}=\frac{1}{10}-\frac{1}{5}\)
⇒ v = -10 cm
Hence, the magnification,
m = \(\frac{v}{u}=\frac{-10}{-5}\) = 2
Hence, the image is on the same side of the lens as an object (palm) and it is virtually erect and magnified. (2)
Question 33.
(i) Name the property of baking soda responsible for the following uses:
(a) As an antacid
(b) baking industry
(c) soda-acid fire extinguisher
(ii) There is a unique acid that, unlike other acids, does not release hydrogen gas when it reacts with metals, except for two specific metals. Provide evidence to support this statement.
Answer:
(i) (a) It is alkaline as it neutralizes the excess acid produced in our stomach and gives us relief from acidity. So, it is used as an antacid.
(b) Baking soda releases carbon dioxide gas which makes the cake or bread soft and spongy. So, it is used in the baking industry.
(c) Baking soda and sulphuric acid present in soda-acid fire extinguishers react to release carbon dioxide gas and this gas is a non-supporter of combustion thus, cutting air supply and the fire gets extinguished.
(ii) Acids like HCl and sulphuric acid react with metals to liberate hydrogen gas.
Zn + 2HCl → ZnCl2 + H2
Mg + H2SO4 → MgSO4 + H2
But nitric acid does not react with metals to liberate hydrogen gas as it is a strong oxidising agent. But magnesium and manganese metal when react with very dilute nitric acid they liberate hydrogen gas.
Zn + 4HNO3 → Zn(NO3)2 + 2H2O + NO2
Mg + 2HNO3 → Mg(NO3)2 + H2
Mn + 2HNO3 → Mn(NO3)2 + H2
Section – D
Questions No. 34 to 36 are long answer questions.
Question 34.
Neha observed the following cases and some questions arose in her mind listed below. Help her to find them out. Why does calcium start floating when added to water? Also, why most of the metals do not give hydrogen while reacting with nitric acid? Write an equation for the reaction of iron with steam. Name the compound of iron obtained.
Or
(a) What is the difference between combustion and oxidation? Under what condition an oxidation reaction can be called combustion? Illustrate your answer with one example in each case.
(b) Yashi took a thin zinc plate and kept it in a glass container having CuSO4 solution. On examination, it was found that the blue colour of the solution was getting lighter and lighter. After a few days when the zinc plate was taken out of the solution, several small holes were noticed in it. State the reason and write the chemical equation of the reaction.
Answer:
The reaction of calcium with water is less violent. The heat evolved is not sufficient for hydrogen to catch fire.
Ca (s) + 2H2O (l) → Ca(OH)2 (aq) + H2 (g) (2)
Calcium starts floating because the bubbles of hydrogen gas formed stick to the surface of the metal. Most of the metals do not give hydrogen while reacting with nitric acid because HNO3 is a strong oxidizing agent. It oxidizes the H2 produced to water and itself gets reduced to any of the nitrogen oxides (N2O, NO, NO2). (2)
Iron reacts with steam to form iron oxide and hydrogen.
Or
(a) The addition of oxygen or removal of hydrogen from any substance is called oxidation.
e.g. When ethanol is burnt in the air, it produces CO2 and water.
However, when ethanol is heated with alk. KMnO4 or acidified K2Cr2O7, gives ethanoic acid.
Both these reactions are oxidation reactions. In both cases, oxygen has been added or hydrogen has been removed. However, the complete oxidation of an organic compound to form CO2 and H2O is called combustion. Therefore, the oxidation of ethanol to form CO2 and H2O can also be called a combustion reaction. Thus, complete oxidation of an organic compound to form CO2 and H2O is also called combustion while partial oxidation of a compound to give a compound other than CO2 and H2O is called oxidation.
(b) A strip of zinc metal is put in a copper sulphate solution. The blue colour of copper sulphate solution fades gradually due to the formation of colorless, zinc sulphate solution. Since zinc is more reactive than copper, it displaces copper from copper sulphate solution. Zinc metal is consumed and hence several small holes were formed in the zinc strip.
Question 35.
(i) 2 g of ferrous sulphate crystals are heated in a dry boiling tube. Answer the following:
(a) List any two observations.
(b) Name the type of chemical reaction taking place.
(c) Write the chemical equation of the reaction.
(ii) (a) What happens when an aqueous sodium sulphate reacts with an aqueous solution of barium
chloride? State the physical conditions of reactants in which reaction between them will not occurs. Write the chemical equation to show the reaction and what is the type of reaction?
(b) What happens if iron nails are placed in copper sulphate solution for half an hour?
OR
State the following:
(i) pH value of sodium chloride?
(ii) When a solution is added to a cloth strip treated with onion extract, then the smell of onion cannot be detected. State whether the given solution contains an acid or a base.
(iii) One animal and one plant whose stings contain formic acid (or methanoic acid).
(iv) How is the concentration of hydronium ions affected when a solution of an acid is diluted?
(v) What is the common name of water soluble bases?
Answer:
(i) (a) Two observations are:
- Green colour ferrous sulphate crystals will first turn into a dirty white solid and then into a brown residue.
- A gas is evolved with a pungent, suffocating smell.
(b) It is a thermal decomposition reaction.
(c) 2FeSO4 \(\rightleftharpoons\) Fe2O3 + SO2 + SO3.
(ii) (a) When an aqueous solution of sodium sulphate reacts with an aqueous solution of barium
chloride, the product formed is barium sulphate i.e., a white precipitate. The reaction will not take place if the reactants are in a solid state. It is a double displacement type of reaction.
BaCl2(aq) + Na2SO4(aq) → BaSO4(s) + 2NaCl(aq)
(b) When iron nails are placed in copper sulphate solution for half an hour, iron sulphate solution and copper metal is formed.
CuSO4(aq) + Fe(s) → FeS04(aq) + Cu(s)
This reaction occurs because iron is more reactive than copper. Also, a brown substance will be deposited on the iron nails. The deposited substance is nothing but copper.
OR
(a) 7
(b) Base
(c) Animal that contains formic acid- ant. Plant that contains formic acid-nettle plant.
(d)The concentration of hydronium ion decreases.
(e) Alkalis
Question 36.
The diagram shown below is an electric circuit in which a 7.2 Ω resistor is connected in series with the parallel combination of 8 Ω and 12 Ω resistors. Power is supplied to the circuit with a 6V battery.
In the circuit diagram given above, find the
(a) the total resistance of the circuit,
(b) the total current flowing in the circuit and
(c) the potential difference across R1.
Or
(a) Heating elements of electrical heating devices are made up of an alloy rather than a pure metal. Give two reasons.
(b) Four resistors of 4 Ω each are joined end to end to form a square. Calculate the equivalent resistance of the combination between two adjacent corners.
(c) Define resistance and 1 ohm.
Answer:
(a) Resistances R2 and R3 are connected in parallel.
Now, resistances 7.2 Ω and 4.8 Ω are connected in series.
So, total resistance = 7.2 + 4.8 = 12.0 Ω (2)
(b) From Ohm’s law,
R = \(\frac{V}{I}\)
I = \(\frac{V}{R}\) = \(\frac{6}{12}\)
Current, I = 0.5A (1)
(c) Current through R1 = 0.5 A
Resistance of R1 = 7.2 Ω
By Ohm’s Law,
R = \(\frac{V}{I}\)
⇒ \(\frac{V}{0.5}\) = 7.2
⇒ V = 7.2 × 0.5 = 3.6 V
The potential difference across the ends of the resistance R1 is 3.6V. (2)
Or
(a) Alloys are used for making electrical heating devices due to the following reasons:
(i) They have a higher resistivity as compared to pure metals.
(ii) They do not oxidize readily at high temperatures. (1)
(b) The resistance between points A and B is given by
(c) The property of a conductor due to which it opposes the flow of current through it is called resistance. The unit of resistance is ohm. One ohm is the resistance of a conductor such that when a potential difference of 1V is applied to its ends, a current of 1A flows through it. (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.
Most human chromosomes have a copy from the mother and a copy from the father, making 22 pairs. However, there is one pair called the sex chromosomes that is different. In women, both sex chromosomes ate the same and are called X. In men, one sex chromosome is a normal-sized X, while the other is a shorter one called Y. This is why women are XX and men are XY. As shown in the diagram, half of the children will be boys, and half will be girls. Regardless of whether they are boys or girls, all children inherit an X chromosome from their mother. The sex of the children is determined by what they inherit from their father. If a child inherits an X chromosome from the father, they will be a girl; if they inherit a Y chromosome, they will be a boy.
(a) Who determines the sex of a child; mother or father?
(b) What will be the gender of a child if it inherits Y chromosome from father?
OR
How many pairs of chromosomes are present in humans?
Answer:
(a) Father determines the sex of a child.
It is therefore thought that genes for femaleness is associated with the X chromosomes and genes for maleness are on Y chromosomes. Hence, the presence of the Y chromosome is a must for the determination of sex of the male person. When fertilisation takes place between a sperm carrying the X chromosome and an egg cell with the X chromosome; then, the developed zygote will contain an XX combination, the child will be a girl. If a sperm carrying Y chromosome unites with an egg cell containing the X chromosome then the zygote will carry XY chromosome and the child will be a boy.
Hence, it can be concluded that the sex of the baby is depended on the father.
(b) The child will be boy (Male)
OR
23 pairs out of which twenty-two of these pairs, are called autosomes, they look the same in both males and females. One pair called sex chromosomes are different in both male and female.
Question 38.
Married women ‘Sita’ used device X made of common metal for preventing pregnancy. This device was put into her uterus by some trained medical professional. Unfortunately, she got pregnant after two months of insertion of the device. She was in shock to learn that her birth control device had failed. Answer the following questions based on the above passage.
(a) Name the birth control device used by the ‘Sita’.
(b) Which metal is commonly used for making device X?
(c) What do you think Sita got pregnant even after using device X?
Or
How does device ‘X’ prevent pregnancy?
Answer:
(a) Copper-T, an intra-uterine device is placed inside the uterus by a doctor or a trained nurse. (1)
(b) Copper metal is commonly used for making device X e.g. copper-T. (1)
(c) Intra-uterine devices are highly effective in preventing unwanted pregnancies. But they came with one disadvantage, they can get expelled anytime without the knowledge of women. (2)
Or
(d) The device ‘X’ namely copper-T releases copper ions that prevent pregnancy by inhibiting the movement of sperm. It is because the copper ion-containing fluid is toxic to sperm. Thus, fertilization is also prevented. (2)
Question 39.
In our homes, we receive the supply of electric power through a main supply (also called mains), either supported through overhead electric poles or by underground cables. One of the wires in this supply, usually with red insulation cover, is called live wire (or positive). Another wire, with black insulation, is called neutral wire (or negative). In our country, the potential difference between the two is 220 V. At the meter-board in the house, these wires pass into an electricity meter through a main fuse. Through the main switch. They are connected to the line wires in the house. These wires supply electricity to separate circuits within the house. Often, two separate circuits are used, one of 15 A current ratings for appliances with higher power ratings such as geysers, air coolers, etc. The other circuit is of 5 A current rating for bulbs, fans, etc. The earth wire, which has insulation of green colour, is usually connected to a metal plate deep in the earth near the house. This is used as a safety measure, especially for appliances with a metallic body, for example, electric press, toaster, table fan, refrigerator, etc. The metallic body is connected to the earth wire, which provides a low-resistance conducting path for the current. Thus, it ensures that any leakage of current to the metallic body of the appliance keeps its potential to that of the earth, and the user may not get a severe electric shock.
(a) What is the potential difference between red wire and black wire?
(b) Why are two separate circuits used in homes?
(c) How is earth wire connected in homes?
OR
(d) How does earth wire act as a safety device?
Answer:
(a) 220 V
(b) Two separate circuits are used, one of 15 A current ratings for appliances with higher power ratings such as geysers, air coolers, etc. The other circuit is of 5 A current rating for bulbs, fans, etc.
(c) The earth wire, which has insulation of green colour, is usually connected to a metal plate deep in the earth near the house.
OR
(d) It is used as a safety measure, especially for appliances with a metallic body, for example, electric press, toaster, table fan, refrigerator, etc. The metallic body is connected to the earth wire, which provides a low-resistance conducting path for the current. Thus, it ensures that any leakage of current to the metallic body of the appliance keeps its potential to that of the earth, and the user may not get a severe electric shock.