Assignment No. 1 Ch 1 Rational Numbers Assignment No. 3 CH 2 - EXPONENTS Assignment No. 3 Ch 3 Square and Square Roots Assignment No. 4 Ch – ALGEBRAIC EXPRESSION Assignment No. 5 Ch – PERCENTAGE AND ITS APPLICATIONS and many more all chapters by BAL BHARATI PUBLIC SCHOOL ,GANGA RAM HOSPITAL MARG, N.D-60
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Q1. Why does a plastic comb rubbed with dry hair attract tiny pieces of paper?
a) Charging by rubbing: Charging of an object by rubbing it with another object is calledcharging by rubbing. c) Charging by induction: Charging a neutral body by bringing it near a charged body is called charging by induction. If the divergence of the leaves increases, the body has similar charge that is the given body is also negatively charged. If the divergence of the leaves decreases, the body has unlike charge that is the given body is positively charged. Q11. What will you observe when the metal cap of an electroscope is touched with a plastic comb rubbed in dry hair? Give reason for your answer.
Ans:Tremors or vibrations caused by the earthquakes which travel in the form of waves within the earth or along the earth's surface, are called seismic waves. Seismograph is an instrument which records these waves.
Ans: Two places in India which are most threatened by earthquake are 1. Kashmir 2. Rann of kutch. Ans: The earth's lithosphere is fragmented into many pieces. Each fragment is called a plate, also called tectonic plate. These plates are in continuous motion i.e. they float over hot magma.
Ans: Lightning conductor is a device used to protect buildings from the damaging effects of lightning. It runs from the top to the bottom, along the outer wall of the buildings or any other object, which is to be protected. If lightning strikes the buildings or any other objects, then the lightning conductor provides an easy and direct path for the lighning bolt to pass to the ground without effecting them. Ans: The process of transferring of charge from a charged object to the earth is called earthing. For our safety, most of the electrical appliances and the mains of the house are connected to earth, so that we can be prevented from getting an electric shock.
23. We can easily charge non-metals like rubber, woollen clothes, plastics, etc. whereas we cannot charge a copper rod by rubbing easily. Why?
Ans: When the metallic rods like copper rod are rubbed, charges does not build on their surface because charges can escape through metals as they are conductors whereas when non-metals like rubber, woollen clothes, plastics, etc. are rubbed, charges will build up on their surface because charges are not conducted through them as they are insulators. Ans: During the development of thunderstorm, air currents move in the upward direction and the water droplets move in the downward direction. These movements causes the seperation of charges. Usually, the negative charges accumulate at the lower part of the clouds and the positive charges are accumulated at its upper part. The positive charges are also accumulated at the ground also. When the accumulation of charges becomes large, a high potential difference is set up between lower part of clouds and earth, which is sufficient to break the insulation of air. As a result, negative and positive charges meet, producing streaks of bright light and sound. This process is called an electric discharge. Ans: An electroscope is used to detect the charge on a body. A plastic comp is taken and it is rubbed on hair. Now, the plastic comb gets charged. The comb is touched with the electroscope plate. The static charges which are developed on the comb travels down the conducting wire and reach the two leaves of aluminium foil. Similar charges are acquired by both the leaves and as a result, they repel each other. Thus, the method of charging an uncharged body by bringing another charged body directly in contact is called charging by conduction. Hence, by this way, an electroscope can be charged through conduction.
Q. During the age between 13-18 year, boys start developing beard and moustaches .Give reason? Answer: This is because of the secretion of sex hormones which bring about change in the body. Q. Why physical exercise and balanced diet are essential during adolescence. Answer: Adolescence is a stage of rapid growth and development. Hence to keep body healthy and fit, physical exercise and balanced diet are essential during adolescence. Q. Why adrenaline hormone is called emergency hormones? Answer: This is because it prepares body to fight and to run fast. It also helps the body to adjust to stress when one is very angry, embarrassed or worried. Q. What is the term used for secretions of endocrine glands responsible for changes taking place in the body? Answer: Hormones is the term used for secretions of endocrine glands responsible for changes taking place in the body. Q. Sweat gland secretes more during adolescence. Why? Answer: During adolescence, sebaceous glands enlarge and produce more sebum under the influence of hormones called androgens. Q. What will happen if a person does not take iodized salts? Answer: Deficiency of iodine in diet causes hypothyroidism due to which thyroid gland increase in size forming exopthalmic goiter. Q. Why do acne and pimple appear during adolescence? Answer: This is because of the increased activity of sebaceous glands (oil glands) in the skin. Sebaceous glands produce a substance called sebum, which is responsible for keeping the skin and hair moisturized. If sebum gets trapped in the pore, acne can develop. Q. Some gland does not have duct. How are their secretion transported in the body? Answer: Gland that does not have duct is called ductless gland like Endocrine glands. These gland release hormones directly into the blood stream. The blood transports their secretion in the body to target organ. Q. Give reasons for the following (a) Tadpoles growing in iodine deficient water have retarded growth. Answer. The process of growth and development is regulated by thyroxine hormone which is produced by thyroid gland. Iodine is required for thyroxine production. That is why retarded growth is seen in tadpoles living in iodine deficient water. (b) Voice becomes hoarse in adolescent boys. Answer. Sometimes the muscles of the growing voice box go out of control and the voice becomes hoarse. (c) Females have no role in determining gender of a child. Answer. Male has both X and Y chromosomes but a female has only two X chromosomes . When sperm containing Y chromosomes fertilize the egg leads to a boy off spring (XY) . Hence, Females have no role in determining gender of a child. Download full E-Study solution
For more related material - 8th BIOLOGY
Q. What is reproduction? Why it is an essential life process? Or, explain the importance of reproduction in organism. Answer: Reproduction is process of producing new individual. Living organism produce young ones of their own kind by the process of reproduction. Reproduction is essential for the continuation of life from one generation to next generation. It ensures the continuation of similar kinds of individuals, generation after generation. Q. What are the different modes by which animals reproduce? Answer: there are two modes by which animals reproduce. These are: (i) Asexual reproduction and (ii) Sexual reproduction Q. Describe asexual reproduction Answer: Asexual reproduction is kind of reproduction in which single individual new individual of its own kinds. The off spring produced by asexual reproduction are similar to parents and are called clones very small animals like hydra and microscopic organisms like amoeba . Q. How new individuals developed in hydra? Answer: Hydra reproduces by budding. In each hydra, there may be one or more bulges. These bulges are called buds. These buds detached from parent body and develop into new individuals. Q. How new individuals developed in amoeba? Answer: Amoeba reproduces by binary fusion. Amoeba splits its body into two, each part receiving a nucleus and two new amoebae are produced. Q. Write some basic feature of a sexual Reproduction? Answer: Asexual Reproduction Basic features (i) Only one parent organism is involved. (ii) New organisms are genetically identical to the parent(clones) (iii)No gamete formation iv) Cell division involved – mitotic Q. Differentiate between (a) Binary fission and Multiple fission (b) fission and budding (c) fission and fragmentation Answer: Differences between binary fission and multiple fission (a) A single parent organism divides into two new organisms. e.g. Amoeba, Pramecium, Euglena (b) Only single parent organism divides into many new organisms. eg. Plasmodium. Differences between fission and budding Fission (a) A single parent organism divides into two or many new organisms. (b) Parental identity is lost (c) Amoeba, Paramecium, Plasmodium Budding (a) Parent organism forms a bud (outgrowth), it gets separated &form a new organism. (b)Parental identity is maintained (c) Hydra, Yeast ( Unicellular Fungus) Differences between fission & fragmentation Fission (i) It occurs in unicellular organisms (ii)The nucleus & cytoplasm of the parent cell divides & produce two daughter cells. (iii)The daughter cells formed are equal in size. (iv)For example : Amoeba, Euglena Fragmentation (i) It occurs in multicellular organisms. (ii)The organism breaks into two or more parts &each part grows into a new organism. (iii) The new organisms formed are usually unequal in size. (iv) for example : Spirogyra Q. Describe about cloning? Answer: Cloning is the production of an exact copy of a cell, any other living part, or a complete organism. Cloning of an animal was successfully performed for the first time by Ian Wilmut and his colleagues at the Roslin Institute in Edinburgh, Scotland. They cloned successfully a sheep named Dolly . Dolly was born on 5th July 1996 and was the first mammal to be cloned. During the process of cloning Dolly, a cell was collected from the mammary gland of a female Finn Dorsett sheep Q. Describe the process of fertilization in human body? Download full E-notes
Definition :- An Arithmetic Progression is a sequence in which the difference between a term and it’s preceding term is a constant. The constant is the common difference (c.d) and is denoted by ‘d’. (The Arithmetic Progression is abbreviated as A.P). The general form and term of an A.P : T1, T2, T3 ………….. Tn .......... be an A.P T2 –T1 = T3 –T2 = T4 –T3 = ………….. = Tn – Tn-1 = d Let T1 = a = a + (1 – 1) d ∴ T2 = T1 + d = a + d = a + (2 – 1)d T3 = T2 + d = a + 2d = a + (3 – 1)d T4 = T3 + d = a + 3d = a + (4 – 1)d …………………………………. Tn = Tn-1 + d = a + (n – 1)d ∴a, a + d, a + 2d, a + 3d, ...................., a + (n – 1)d is the general form of an arithmetic progression with ‘a’ as the first term and having common difference ‘d’. This is the Standard form of an A.P. The last term a + (n – 1) d is denoted by Tn or l Note : 1. In an A.P succeeding term of a given term is obtained by adding ‘d’to it. [Tn+1 = Tn+ d]. 2. In an A.P preceding term of a given term is obtained by subtracting ‘d’ from it [Tn-1 = Tn – d]. 3. Tn = a + (n – 1)d is the general term of an A.P Find the nth and the 20th terms of the A.P. 3, 7, 11, 15, ............... Solution : a = 3, d = T2 – T1 = 7 – 3 = 4, Tn = ?, T20 = ? Tn = a + (n – 1)d. Tn = 3 + (n – 1)4 = 3+4n–4 Tn = 4n – 1 T20 = 4(20) – 1 T20 = 79 (OR) T20 = 30 + (20 – 1)4 = 80 – 1 = 3 + 19 x 4 T20 = 3+76=79 How many terms are there in the A.P. 4, –1, –6, ............., (–106) Solution : Given : a = 4, d = –5, Tn = –106, n = ? Tn = a + (n – 1)d. ∴ a + (n – 1)d = Tn 4 + (n – 1) (–5) = –106 4 – 5n + 5 = –106 –5n + 9 = –106 ∴ –5n = –106 – 9 ∴ –5n = –115 n = 23 There are 23 terms in the given A.P. Q . The fourth and eighth terms of an A.P. are in the ratio 1 : 2 and tenth term is 30, Find the Common difference and the first term.[ d = 3; a = 3] Q. The angles of a triangle are in A.P. The smallest angle is 300. Show that the triangle is a right angled triangle.[ In triangle ABC, let us say ∠A = 30 0 then <∠B = 300+d and <∠C = 300 +2d ] Q. Find the three numbers of an A.P. whose sum is 12 and their product is 48. [2, 4 and 6 (or) 6, 4 and 2] Q. Find the sum of all positive multiples of 3 less than 50 [408] Sum of First n Terms of an AP Let us denote the first term of an AP by a1, second term by a2 , . . ., nth term by an and the common difference by d. Then the AP becomes a1, a2, a3. . . a + [n-1]d Let S denote the sum of the first n terms of the AP. We have S = a + (a + d ) + (a + 2d ) + . . . + [a + (n – 1) d ] ---------------------(i) Rewriting the terms in reverse order, we have S = [a + (n – 1) d ] + [a + (n – 2) d ] + . . . + (a + d ) + a ----------------(ii) On adding (i) and (ii), term-wise. we get 2S = [2a + (n – 1) d ] + [2a + (n – 1) d ] + . . . + [2a + (n – 1) d ] ----- n times S = [2a + (n – 1) d ] OR, S = [a + a + (n – 1) d ] = [a + an ] OR, if there are only n terms in an AP, then an = l, the last term. S = (a + l ) This form of the result is useful when the first and the last terms of an AP are given and the common difference is not given. Find the sum of all natural numbers between 91 and 170 which are divisible by 5. Solution : The numbers between 91 and 170 which are divisible by 5 are 95, 100, 105, ...... 165 a = 95 ; d = 5 First find the number of terms in the A.P. Tn = 165 ∴ a + (n – 1)d = 165 95 + (n – 1)5 = 165 ∴ 95 + 5n – 5 = 165 ∴ 5n + 90 = 165 5n = 165 – 90 n = 15 Sn = n/2 (a + l) =15/2 (95 + 165) =1950 The sum of n terms of an arithmetic series is Sn = 2n2 + 6n. Find the first term and the common difference. Solution : Given : Sn = 2n2 + 6n and S1 = T1 S1 = 2(1)2 + 6(1) = 2+6 = 8 T1 = 8 ∴ a = 8 To find 'd' S2 = 2(2)2 + 6(2) = 2(4) + 12 = 8 + 12 ∴ S2 = 20 S2 = T1 + T2 = 20 20 = 8 + T2 T2 = 12 d = T2 – T1 = 12 – 8 Q. How many terms of the series 10 + 8 + 6 + ............ should be added to get the sum –126. [n = 18 ] Q. Sanganbasava rides a bicycle from his home to the ashram. He covers 125 meters at the end of first minute, 135 meters at the end of second minute and so on. If he reaches the Ashram at the end of 10 minutes. Find the distance between hishome and ashram. [1.7 Kms] Q. Find the A.P in which a)Tn = 2n + 1 b) Tn = 4 – 5n c) Sn = 5n2 + 3n [I. a) 3, 5, 7, ............. b) –1, –6, –11, .............. c) 8, 18, 28 ............] Q. Find the sum of the Arithmetic series which contains 25 terms and whose middle term is 20. [500] Q. The angles of a quadrilateral are in A.P. If the smallest angle is 150, find the angles of the quadrilateral.[ 650, 115 0 and 1650] Q. Veershree climbed 23 steps of Golgumbaz in the first minute. After that she climbed two steps less than what she had climbed in the previous minute. If she reached the whispering gallery of Golgumbaz after 7 minutes how many steps did she climb to reach the whispering gallery? [119] For more Test paper/Solved paper/E-Book Visit Arithmetic progressions
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