(iv) Section C question no. 27 to 33 are short answer type questions, carrying 3 marks each. Answers to these questions should in the range of

Section-A

1. State Newlands’ law of octaves.

Or

The atomic number of three elements A, B and C are 12, 18 and 20 respectively. State giving reason, which two elements will show similar properties.

[CBSE 2014]

Ans. According to this law, when the elements are arranged in the increasing order of their atomic masses, the properties of eighth element are similar to the first element, like the notes of music.

Or A (12) = 2, 8, 2 B (18) = 2, 8, 8 C (20) = 2, 8, 8, 2

Elements A and C will show similar properties because both A and C have 2 electrons in their outermost orbit.

2. Draw the electron dot structure of H

S.

Ans. ₁H = 1 ₁₆S = 2, 8, 6

The electron dot structure of H₂S is:

S

H H

3. When magnesium is burnt in air then:

(a) Magnesium is reacting with oxygen (b) Magnesium is reacting with nitrogen

(c) Magnesium is reacting with carbon

(d) Magnesium is reacting with carbon dioxide Ans. (a) Magnesium is reacting with oxygen.

4. One half of a convex lens is covered with a black paper. Will this lens produce a complete image of the object? Explain your observation.

Ans. It will form a complete image but intensity (brightness) of the image will be half as that with complete lens exposed. Nature, size and location of the image will be the same since light from all parts of the object reach the exposed part of the lens.

5. A spherical mirror produces an image of magnification

1 on a screen placed at a distance of 50 cm from the mirror. What is the type of mirror?

Ans. Because of negative magnification, the image formed is real.

Hence, it is a concave mirror.

6. What do you call the phenomenon due to which we get light from the sun before sunrise?

Or

What would have been the colour of the sky, if the Earth had no atmosphere?

Ans. The phenomenon is known as atmospheric refraction.

Or

The colour would have been black in the absence of atmosphere.

Time : 3 hrs.

Max. Marks : 80

(i) The question paper comprises four sections A, B, C and D. There are 36 questions in the question paper. All questions are compulsory.

(ii) Section–A — question no. 1 to 20 — all questions and parts thereof are of one mark each. These questions contain multiple choice questions (MCQs), very short answer questions and assertion - reason type questions. Answers to these should be given in one word or one sentence.

(iii) Section–B — question no. 21 to 26 are short answer type questions, carrying 2 marks each. Answers to these questions should in the range of 30 to 50 words.

(iv) Section–C — question no. 27 to 33 are short answer type questions, carrying 3 marks each. Answers to these questions should in the range of 50 to 80 words.

(v) Section–D — question no. - 34 to 36 are long answer type questions, carrying 5 marks each. Answer to these questions should be in the range of 80 to 120 words.

(vi) There is no overall choice. However, internal choices have been provided in some questions. A student has to attempt only one of the alternatives in such questions.

(vii) Wherever necessary, neat and properly labelled diagrams should be drawn.

SAMPLE

QUESTION PAPER

General instructions Detailed Solutions ^{SCIENCE Class X with} 4

(Question-Answer)

7. What is meant by solenoid?

Ans. It is coil of many circular turns of insulted copper wire wound on a cylindrical insulating body (i.e., cardboard, etc) such that its length is greater than its diameter.

8. Draw a closed circuit diagram consisting of a 0.5 m long nichrome wire XY, an ammeter, a voltmeter, four cells of 1.5 V each and a plug- key.

Ans.

(1.5 V × 4)

X Y

+V –

A+ 0.5 m –

[1]

9. An electric heater is rated at 2 kW. Calculate the cost of using it for 2 hours daily for the month of September, if each unit costs ` 4.

Show how would you join three resistors, each of Or resistance 9

so that the equivalent resistance of the combination is 13.5

.

Ans. Electric energy consumed by heater in one day = Power × Time

= 2 kW × 2 h = 4 kWh

Electric energy consumed by heater in the complete month of September

= 4 × 30 = 120 kWh

= 120 units [∵ 1 unit = 1 kWh]

Cost of using the heater = 120 × 4 = ` 480

Or

If two 9 W resistors are connected in parallel, then the equivalent resistance is (9/2) W= 4.5 W.

9 W 9 W

A B

9 W

This combination is connected in series with a 9 W resistor to get an overall equivalent resistance of (9 + 4.5) W = 13.5 W.

10. If we cross pure-bred tall (dominant) pea plant with pure-bred dwarf (recessive) pea plant, we will get pea plants of F

generation. If we now self-cross the pea plant of F

generation, then we obtain pea plants of F

generation. What do the plants of F

generation look like?

Ans. All plants of F₁ generation will be tall.

11. Write the function of saliva in the human alimentary canal.

Or

List any two functions of the tongue.

Ans. (i) (a) Saliva: It contains an enzyme, salivary amylase that breaks polysaccharide starch into disaccharide maltose (sugar).

(b) HCl in Stomach: HCl provides an acidic medium required for the action of enzymes and to destroy the bacteria present in food.

(c) Bile Juice: Bile juice neutralises gastric acid that enters small intestine from stomach to provide alkaline pH for the action of pancreatic and intestinal digestive enzymes.

(d) Villi: It increases the surface area of the inner lining of the intestine, thus, enhancing the capacity of absorption by the wall of the intestine.

Or Functions of Tongue:

(i) It helps in mastication of food.

(ii) It bears taste buds and helps in the sensation of tasting of food.

(iii) It takes part in the modification of sound production.

(iv) It acts as a brush and cleans the teeth.

(v) It aids in deglutition of food.

12. In the figure given alongside, the various trophic levels are shown in the form of a pyramid. At which trophic level, the maximum energy is available?

L₄ L₃ L₂ L₁

Or

What are the problems caused by the non- biodegradable wastes that we generate?

Ans. Maximum energy is available at L₁. Or

The problems caused by non-biodegradable wastes are:

(i) Biomagnification.

(ii) Increase in air pollution when burnt.

(iii) Soil pollution that leads to loss of fertility.

(iv) Killing of useful microorganisms.

(v) Water pollution making water unfit for drinking.

(vi) Blockage of the water flow and blocked drains. (Any two)

13. What is DNA?

Ans. Deoxyribonucleic Acid (DNA) is a molecule which carries the hereditary information in a coded form from one generation to the other in all the organisms.

3

Sample Question Paper 4 for 2021 Board Examination Directions (Q. Nos. 14-16): Each of the following questions consists of two statements, one is Assertion (A) and the other is Reason (R). Select the correct answer to these questions from the codes (a), (b), (c) and (d) as given below:

(a) Both A and R are true and R is correct explanation of A.

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

(c) A is true but R is false.

(d) A is false but R is true.

14. Assertion(A) : Decomposers act as cleaning agents of the environment.

Reason(R) : The decomposers recycle waste material in the hydrosphere.

Ans. (c) A is true but R is false.

15. Assertion(A): Atomic radii decrease from Li to F.

Reason(R): Nuclear charge increases due to increase in atomic number therefore force of attraction between nucleus and valence electrons increases.

Or

Assertion(A): Atomic size of Mg is more than that of Na.

Reason(R): Mg has less effective nuclear charge, i.e. less number of protons attract less number of electrons than Na.

Ans. (a) Both A and R are true and R is correct explanation of A.

Or (d) A is false but R is true.

16. Assertion(A): The energy flow through different steps in the food chain is unidirectional.

Reason(R): The energy which is captured by autotrophs does not revert back to the solar input and passes to the herbivores.

Ans. (a) Both A and R are true and R is correct explanation of A.

Directions (Q. Nos. 17-20): Each question contain five sub-parts. You are expected to answer any four sub-parts in each question.

17. Sexual reproduction is the most common method of reproduction in flowering plants. This means that two sexes are involved in reproduction in flowering plants. The flowers, which contain only one sex organ, either stamens or carpels are called unisexual flowers whereas flowers which contain both the sex organs are called bisexual flowers.

(i) Which of the following statements are true for flowers?

(a) Flowers are always bisexual

(b) After fertilisation they give rise to fruits

(c) They are the sexual reproductive organs (d) Both (b) and (c)

Ans. (d) Both (b) and (c)

(ii) Which of the following statements are true for sexual reproduction in flowering plants?

I. It requires two types of gametes II. Fertilisation is a compulsory event

III. It always results in the formation of zygote IV. Offsprings formed are clones

(a) I and IV (b) I, II and III (c) I, II and III (d) II, III and IV Ans. (c) I, II and III

(iii) Study the given figure and choose the correct combination of the parts marked A, B and C provided below:

A B C Fig. A : Germination

Fig. B : Germination of Pollen on Stigma R

Q

S

P (a) cotyledon, plumule and radicle (b) plumule, radicle and cotyledon (c) plumule, cotyledon and radicle (d) radicle, cotyledon and plumule Ans. (c) plumule, cotyledon and radicle

(iv) The length of pollen tube depends on the distance between:

(a) pollen grain on upper surface of stigma and ovule (b) upper surface of stigma and lower part of style (c) pollen grain and upper surface of stigma

(d) pollen grain in anther and upper surface of stigma.

Ans. (a) pollen grain on upper surface of stigma and ovule

(v) Which of the following is the correct sequence of events of sexual reproduction in a flower?

(a) Pollination, fertilisation, embryo, seedling (b) Seedling, embryo, fertilisation, pollination (c) Embryo, seedling, fertilisation, pollination (d) Pollination, fertilisation, seedling, embryo Ans. (a) Pollination, fertilisation, embryo, seedling

18. A metal salt MX when exposed to sunlight splits up to form metal M and a gas X

. Metal M is used in making ornaments whereas gas X

is used in making bleaching powder. The salt MX is itself used in black and white photography.

(i) What do you think Metal ‘M’ is?

(a) Magnesium (b) Chlorine (c) Silver (d) Iron Ans. (c) Silver

(ii) What could be the gas X₂?

(a) Chlorine (b) Oxygen (c) Hydrogen (d) Bromine Ans. (a) Chlorine

(iii) Name the metal salt MX?

(a) PbO (b) AgCl (c) CaO (d) AgBr Ans. (b) AgCl

(iv) Electrolysis of water is a decomposition reaction.

The mole ratio of hydrogen and oxygen gases liberated during electrolysis of water is:

(a) 1 : 1 (b) 2 : 1 (c) 4 : 1 (d) 1 : 2 Ans. (b) 2 : 1

(v) Which among the following statement(s) is(are) true? Exposure of MX to sunlight for a long duration turns grey due to:

I. the formation of M by decomposition of MX II. sublimation of MX

III. decomposition of X₂ gas from MX IV. oxidation of MX

(a) I only (b) I and III (c) II and III (d) IV only Ans. (a) I only

19. Shivani wanted to study the formation of different types of images by spherical lenses. So she bought two lenses X and Y. Out of which when an object is placed 10 cm in front of lens X, the image is real, inverted, magnified and formed at a great distance.

But when the same object is placed 10 cm in front of lens Y, the image formed is real, inverted and of same size as the object.

(i) What is the focal length of lens X?

(a) 10 cm (b) 5 cm (c) 20 cm (d) 15 cm Ans. (a) 10 cm

Explanation: X is concave in nature because image is real. In concave mirror, when object is placed at focus, image is formed at infinite i.e. at a great distance. Thus, focal length of X is 10 cm.

(ii) What is the focal length of lens Y?

(a) 5 cm (b) 20 cm

(c) 15 cm (d) 10 cm

Ans. (a) 5 cm

Explanation: X is cancave in nature because image is real. When object is placed at centre of curvature, image is real, inverted and of same size as object.

Thus, radius of curvature of mirror Y is 10 cm.

⇒ f =R = =

2 10

2 5 cm

(iii) Which one of the following materials cannot be used to make a lens?

(a) Clay (b) Glass

(c) Plastic (d) Both (a) and (c) Ans. (a) Clay

(iv) Linear magnification produced by lens Y can be:

(a) less than 1 or more than 1 (b) less than 1 or equal to 1

(c) less than 1, more than 1 or equal to 1 (d) more than 1 or equal to 1

Ans. (c) less than 1, more than 1 or equal to 1

(v) Lens X produces a magnification of +5. The object is placed:

(a) beyond 2f (b) at less than f (c) between f and 2f (d) at focus Ans. (b) at less than f

20. The resistivity of a substance is numerically equal to the resistance of a rod of that substance which is 1 metre long and 1 square metre in cross-section.

The resistivity of a substance does not depend on its length or thickness but it depends on the nature of the substance and temperature. The metals and alloys have very low resistivity whereas insulators have resistivity of the order of 10

to 10

m.

The table given below shows the resistivity of five materials P, Q, R, S and T.

P 5.20

10

m Q 110

10

m R 2.60

10

m S 10.0

10

m T 1.70

10

m

(i) Which substance is the best conductor of electricity?

(a) P (b) R (c) T (d) Q Ans. (c) T, because it has least resistivity.

(ii) Which substance would you advise to be used for making heating elements of electric irons?

(a) Q (b) P (c) R (d) S Ans. (a) Q, because it has maximum resistivity.

(iii) Which two substances should be used for making electric wires?

(a) P and R (b) R and T (c) S and T (d) P and S Ans. (b) R and T

(iv) Electrical resistivity of a given metallic wire depends upon:

(a) its length (b) its shape (c) nature of the material (d) its thickness Ans. (c) natural of the material

5

Sample Question Paper 4 for 2021 Board Examination

section area 1.0 mm² is 30 W. The resistivity of material is:

(a) 0.3 × 10^-6 Wm (b) 0.1 Wm (c) 1 × 10^-4 Wm (d) 1.0 × 10^-7 Wm

Ans. (d) Given, l = 300 m, A = 1 mm²= 10^-6m² and R = 30 W We know that, ρ =RA = × ⁻ = × ⁻

l

30 10

300 ⁶ 0 1 10. ⁶ r= 1.0 × 10^-7W m

Section-B

21. Compare the functioning of alveoli in lungs and nephrons in the kidneys with respect to their structure and functioning.

Or

What are the differences between the transport of material in xylem and phloem?

Ans. Comparison of functioning of alveoli and nephron:

[½]

Basis of

Difference Alveoli Nephron

1. Structure Alveoli are tiny balloon-like structures present inside the lungs.

Nephrons are tubular structures present inside the kidneys.

2. Functions The exchange of O₂ and CO₂ takes place between the blood of the capillaries that surround the alveoli and the gases present in them.

Alveoli are the site of gaseous exchange.

The blood enters the kidney through the renal artery which branches into many capillaries in the glomerulus.

The water and solute are transferred to the nephron at Bowman’s capsule. Then the filtrate moves through the proximal tubule, distal tubule and collecting duct. The collecting duct collects the urine from many nephrons and passes it to the ureter. During the flow of filtrate, some substances such as glucose, amino acids and water are selectively reabsorbed.

Nephrons are the basic filtration unit.

Or

[1½]

Difference between xylem and phloem:

[1]

Basis of

Difference Xylem Phloem

1. Working Xylem tissue helps in the transport of water and minerals.

Phloem tissue helps in the transport of food.

2. Transportation Water is transported upwards from roots to all other plant parts.

Food is transported in both upward and downward directions.

[1]

22. (i) What is transpiration? List its two functions.

(ii) Write the function of bile juice in human alimentary canal.

Ans. (i) The release of water in the form of vapours from the aerial parts of the plant through the pores called stomata, is called transpiration.

Its functions are:

(a) It helps in the absorption and upward movement of water and minerals dissolved in it from roots to leaves.

(b) It helps in the regulation of temperature. [1]

(ii) Bile Juice: Bile juice neutralises gastric acid that enters small intestine from stomach to provide alkaline pH for the action of pancreatic and intestinal digestive enzymes. [1]

23. Give suitable reason for the following statements:

(i) We feel burning sensation in the stomach when we overeat.

(ii) The crystals of washing soda change to white powder on exposure to air.

Or

You have four solutions A, B, C and D. The pH of solution A is 6, B is 9, C is 12 and D is 7.

(i) Identify the most acidic and most basic solutions.

(ii) Arrange the above four solutions in the increasing order of H

ion concentration.

[CBSE 2012]

Ans. (i) Due to overeating, excess of hydrochloric acid is produced in stomach which causes burning sensation. [1]

(ii) Washing soda is sodium carbonate decahydrate (Na₂CO₃10H₂O) but when it is exposed to air, it loses its water of crystallisation and changes to white powder (Na₂CO₃). [1]

Or

(i) ‘A’ is the most acidic and ‘C’ is the most basic solution. [1]

(ii) C (10^-12) < B (10^-9) < D (10^-7) < A (10^-6) [1]

24. A part of the periodic table is given below:

Li Na

K Be Mg Ca

B Al Ga

C Si

N P As

O S Se

F Cl Br Ge

Based on the given table:

(a) As we move horizontally from left to right, what happens to the non-metallic character of the elements?

(b) As we move horizontally from left to right, what happens to the valency of elements?

Ans. (a) On moving from left to right, the non-metallic character increases. [1]

(b) On moving form left to right, the valency of elements increases from 1 to 4 and then decreases to zero. [1]

25. ‘A convex lens can form a magnified erect as well as a magnified inverted image of an object placed in front of it’. Draw ray diagram to justify this statement stating the position of the object with respect to the lens in each case.

Ans. A convex lens of focal length ‘f ’ can produce:

(i) A magnified and erect image only when the object position is between its focus ‘F’ and optical centre ‘O’ of the lens.

2F2

F2

A O F1

2F1

A’

B’

B

[½]

(ii) A magnified and inverted image can be obtained when an object is kept in the following positions:

(a) Between F₁ and 2F₁.

2F1 A

B

B′

F1 O

F2 2F2 A’

[½]

(b) At focus F₁.

AF1

F2

O B

So, for the given positions of the object for a convex lens, the

given statement is true. [1]

26. The figure below shows three cylindrical copper conductors along with their face areas and lengths.

Discuss in which geometrical shape, the resistance

will be highest.

A A/2

L 2 L

(i) (ii)

2 A L/2(iii)

Ans. For geometrical shape shown in figure (i), the value of resistance

R L

1= ρA In figure (ii), the value of resistance

R L

A

L

A R

2 2 1

2 4 4

= =  

ρ ρ  = /

In figure (iii), the value of resistance

R L

A

L A

3 2 R1

2 1

4 4

= =  

ρ / ρ  =

Therefore, the resistance in the geometrical shape in figure (ii),

will be the highest. [2]

Section-c

27. What is DNA copying? State its importance.

Or

Explain with the help of suitable example why certain traits cannot be passed on to the next generation. What are such traits called?

Ans. DNA copying is the process of production of new DNA molecules from an existing DNA molecule through a chemical reaction. [1]

DNA is important for the following reasions:

(i) It helps in the transmission of characters from parents to offspring.

(ii) It contains the information necessary for the inheritance of

features. [2]

There are some traits which are developed during the lifetime of Or an individual. For example, the gall bladder, which many people get removed by surgery due to certain complications. The children of these people are born with a gall bladder. These traits involve change in non-reproductive cells which are not transferred to germ cells. So, these traits cannot be passed on to the next generation. Traits whose characteristics are not controlled by genes and cannot be transferred from one generation to the next generation are called acquired traits. [3]

7

Sample Question Paper 4 for 2021 Board Examination 28. What is meant by food chain? ‘The number of

trophic levels in a food chain is limited.’ Give reason to justify this statement.

Ans. A food chain is the series of organisms that take part at various biotic levels. At each trophic level in a food chain, the utilisation of energy takes place for the maintenance of organisms which occur at that trophic level and energy is lost as heart. In this way, organisms in each trophic level pass on less energy to the next trophic level than they receive. The longer the food chain, the less is the energy available to the final member of the food chain which will be insufficient for their survival. [3]

29. (i) Pick out the incorrect pair and correct them:

(a) Planaria

Regeneration

(b) Bryophyllum

Spore formation (c) Amoeba

Binary fission

(ii) Mention two advantages of the method used in the corrected pair and also define it.

[CBSE 2020]

Ans. (i) Incorrect —Bryophyllum = Spore formation.

Correct—Bryophyllum = Vegetative propagation. [1]

(ii) Vegetative Propagation: It is an asexual method of plant reproduction in which a new plant grows for vegetative parts of the plants like leaf, roots and stem. [1]

Two advantages of vegetative propagation are:

(a) Plants raised by this method can bear fruits earlier.

(b) Produce genetically similar plants. [1]

30. A sulphate salt of group 2 element of the periodic table is a white, soft substance, which can be moulded into different shapes by making its dough. When this compound is left in open for some time, it becomes a solid mass and cannot be used for moulding purposes. Identify the sulphate salt and state why does it show such a behaviour.

Give the reaction involved.

Ans. The substance which is used for making different shapes is plaster of pairs. Its chemical name is calcium sulphate hemihydrate (CaSO₄. 1/2H₂O). Due to the presence of water of crystallisation, it is soft and can be moulded into different shapes by making its dough. When this compound is left in open for some time, It becomes a solid mass because it absorbs moisture and set to form a hard, solid mass known as gypsum. The reaction Involved is:

CaSO .1

2H O 11

2H O CaSO .2H O

4 2 + 2 → ₄ 2 [3]

Plaster of Water Gypsum

paris

31. Two elements ‘P ’ and ‘Q ’ belong to the same period of the modern periodic table and are in Group 1

and Group 2 respectively. Compare their following characteristics in tabular form:

(i) The number of electrons in their atoms (ii) The sizes of their atoms

(iii) Their metallic characters

(iv) Their tendencies to lose electrons (v) The formula of their oxides

(vi) The formula of their chlorides

Ans.

S.No. Group 1 Group 2

(i) They have one

valence electron. They have two valence electrons.

(ii) They are large in

size. They are smaller in size.

(iii) They are more

metallic. They are less metallic.

(iv) They can lose

electrons easily. They have less tendency to lose electrons than group 1 elements.

(v) P₂O is the formula of

their oxides. QO is the formula of their oxides.

(vi) PCl is the formula of

their chlorides. QCl₂ is the formula of their chlorides.

[3]

32. What is meant by reactivity series of metals? State which of the following chemical reactions will take place giving suitable reason for each.

(i) Zn(s)

CuSO

(aq)

ZnSO

(aq)

Cu(s) (ii) Fe(s)

ZnSO

(aq)

FeSO

(aq)

Zn(s) (iii) Zn(s)

FeSO

(aq)

ZnSO

(aq)

Cu(s)

[CBSE 2009]

Ans. Reactivity series is a list of metals arranged in the order of their decreasing reactivities:

(i) Reaction will take place because Zn is above Cu in the activity series and is more reactive than Cu. [1]

(ii) Reaction will not take place as Fe is below Zn in the activity series and cannot displace Zn from its solution. [1]

(iii) Reaction will take place because Zn is more reactive than Fe.

[1]

33. Why do stars twinkle? Explain.

Ans. Stars emit their own light and they twinkle due to the atmospheric refraction of light. Stars are very far away from the earth. Hence, they are considered as point sources of light. When the light coming from stars enters the earth’s atmosphere, it gets refracted at different levels because of the variation in the air density at different levels of the atmosphere. When atmosphere refracts more starlight towards us, stars appear to be bright and when atmosphere refract less light, stars appear to be dim. Hence, the starlight reaching our eye change continuously and stars appear to twinkle. [3]

Section-D

34. An element ‘A’ which is a part of common salt and kept under kerosene reacts with another element

‘B’ of atomic number 17 to give a product ‘C ’. When an aqueous solution of product ‘C ’ is electrolysed then a compound ‘D’ is formed and two gases are liberated.

(i) What are A and B?

(ii) Identify C and D.

(iii) What will be the action of D on litmus solution?

Why?

(iv) State whether element B is solid, liquid or gas at room temperature.

(v) Write the formula of the compound formed when element B reacts with an element E having atomic number 5.

Or

(i) Identify the compound of calcium which is yellowish white powder and is used for disinfecting drinking water. Write its chemical name and formula. How is it manufactured?

Write the chemical equation for the reaction involved. Also list two other uses of the compound.

(ii) Write the balanced chemical equation of chlor-alkali process.

Ans. (i) A is sodium and B is chlorine.

(ii) C is sodium chloride and D is sodium hydroxide.

(iii) It will turn litmus solution blue because D is a base (NaOH).

(iv) B is a gas at room temperature.

(v) EB ₃ because ₅E = 2, 3

E⁺³ B^-1

E1 B₃ or EB₃ [1 × 5]

Or

(i) The compound is bleaching powder (CaOCl₂). Its chemical name is calcium oxychloride. It is manufactured by reaction of dry slaked lime with chlorine gas.

Ca(OH)₂ + Cl₂ → CaOCl₂ + H₂O [2]

Uses:

(a) It is used for bleaching cotton and linen in the textile industry.

(b) It is used for the preparation of chloroform. [2]

(ii) Chlor-alkali Process:

2NaCl(aq) + 2H₂O(l) → 2NaOH(aq) + H₂(g)+ Cl₂(g) [1]

35. (i) Mention the role of the following organs of human male reproductive system:

(a) Testes

(b) Scrotum

(c) Vas deferens

(d) Prostrate glands

(ii) Write the functions of testosterone.

Ans. (i) (a) Testes: To produce male sex cells called sperms and male sex hormone called testosterone.

(b) Scrotum: To provide optimal temperature to testes for the formation of sperms.

(c) Vas Deferens: To deliver the sperms to the urethra coming from the urinary bladder.

(d) Prostrate Glands: To secrete the fluid which provides nutrition and medium for transport of sperms. [1× 4]

(ii) Functions of testosterone are:

(a) It regulates the formation of sperms.

(b) It brings about changes in appearance in boys during

adolescence. [1]

36. (i) Calculate the heat produced when 96,000 Coulomb of charge is transferred in 1 hr through a p.d. of 50 volts.

(ii) Derive the formula for resultant resistance of three resistances connected in series.

Or

(i) Draw a diagram showing electric motor and label its parts.

(ii) What is the role of split ring in an electric

motor?

(iii) In what way is the right-hand thumb rule different from Fleming’s left-hand rule?

Ans. (i) Given, Q = 96,000 C t = 1 hr = 60 × 60 second I Q

= t =

× 96000

60 60 =80=

3 26 67. A According to Ohm’s Law,

V = IR ^R

V

= =I 50 = 26 67. 1.87 W Heat produced, H = I ²Rt

=( . )26 67²×1 87 60 60. × × = 4788396.87J = 4788396 87=

1000. 4788 4. KJ [2½]

(ii) The given figure shows a combination of three resistors in series.

9

Sample Question Paper 4 for 2021 Board Examination

K V1

+ – V

I+ I –

R1 R2 R3

V2 V3

A

A B C D E F

Resistors in Series

Let the resistors having resistances R₁, R₂ and R₃ be connected in series, I be the current passing through each resistor and V₁,V₂ and V₃ be the potential differences across AB (R₁), CD (R₂) and EF (R₃).

From Ohm’s law,

Potential difference across AB, i.e., V₁ = IR₁ Potential difference across CD, i.e., V₂ = IR₂ Potential difference across EF, i.e., V₃ = IR₃ Total potential difference (V) = V₁ + V₂ + V₃ V = IR₁ + IR₂ + IR₃

V = I (R₁ + R₂ + R₃)

If R_s is the equivalent resistance and V = IR, then IR_s = I (R₁ + R₂ + R₃)

Hence, R_s = R₁ + R₂ + R₃ [2½]

Or

K B

A D

Split rings (P and Q)

X P Q Y

Brushes (X and Y)

+ –

Axle S N

C

A Simple Electric Motor

[2]

(ii) The split rings in electric motor acts as commutator. Its function is to reverse the direction of current flowing through the coil after every half rotation of the coil. [1]

(iii) Right-hand thumb rule is used to find the direction of magnetic field due to a straight carrying conductor whereas Fleming’s left-hand rule is used to find the direction of motion or force acting on the conductor when placed in a magnetic field. [2]