CBSE ADDA

A chemical process in which a substance reacts with oxygen to give off heat is called combustion. The substance that undergoes combustion is said to be combustible . The substances that do not burn on being exposed to flame are called  non-combustible  substances. like stone, glass, iron nails, etc. Ignition temperature :   The lowest temperature  at which a fuel catches fi re is called  its  ignition temperature. Types of combustion : Combustion can be of different types.  It can be spontaneous, rapid, slow or incomplete. Spontaneous combustion : combustion reaction that occurs without the help of any external heat is called

Motion and Rest A body is said to be in the state of rest when it remains in the same position with respect to time. e.g.: The position of trees around the building is not changing with respect to the building. Then the trees are at rest. A body is said to be in the state of motion, when it continuously changes its position with respect to time e.g.:  When we are cycling or running, we are changing position with respect to trees and buildings. we are said to be moving DISTANCE AND DISPLACEMENT Distance is the length of the path covered by a body. It has no sense of direction so it is a scalar quantity. Its SI unit of measurement is  meter or m The distance between the two places is not the same; it depends upon the path chosen. Displacement: The shortest distance, or distance travelled along a straight line, is known as displacement. If we draw a semicircle of radius 10cm. Then, Displacement  =  r + r = 20cm Distance          =  2 p r/2 = 10 x 22/7

TET/CTET Maths sample  Questions Paper 1. A student gets an aggregate of 60% marks in five subjects in the ratio 10: 9: 8: 7: 6. If the passing marks are 50% of the maximum marks and each subjects has the same maximum marks, in how many subjects did he pass the exam? (a) 2         (b) 3         (c) 4         (d) 5                               2 P, Q and R are three consecutive odd numbers in ascending order. If the value of three times P is three less than two times R, find the value of R. (a) 5 (b) 7 (c) 9 (d) 11 3. If log2[log7(x2 - x + 37) ] = 1, then what could be the value of x? (a) 3 (b) 5 (c) 4 (d) None of these 4. After a discount of 11.11%, a trader still makes a gain of 14.28%. At how many percent above the cost price does he mark his goods? (a) 28.56% (b) 35% (c) 22.22% (d) None of these 5. An old man has Rs. (1! + 2! + 3! + ...+ 50!), all of which he wants to divide equally (Without frac

CBSE TEST PAPER 8th Algebric Expression 1 .      Numerical coefficient of 8x 3 yz 2 is ________    2.      Monomial is a ________________ 3.          Write like terms from 2x 2 , 2x, 2x 3 , - 5x, 11x 4                                           4.      Write numerical coefficient of . 3x 3 yza 2   5.      Find area of rectangle with sides 3x and 5y       6.      Factorise 3xy + 9x 2 y 3 7.      Divide 7x 2 y 2 z 2 ÷ 21xyz 8.      Subtract 5x 2 – 4y 2 + 6y – 3 from  7x 2 – 4xy + 8y 2 + 5x – 3y. 9.      Add 4y (3y 2 + 5y – 7) and 2 (y 3 – 4y 2 + 5)          10.   Simplify (a + b) (2a – 3b + c) – (2a – 3b) c.      11.   . Simplify (a + b + c)(a + b – c) 12.   find the products. (i) (2a2 + 9) (2a2 + 5)  (ii) (0.4p – 0.5q) 2   13.   Simplify.  (m 2 – n 2 m) 2 + 2m 3 n 2                14.   Evaluate (i) 998 2   (ii) 297 × 303 (iii) (1.02) 2 – (0.98) 2 15.   Find the value of x 2 +y 2  if x+y =12 and xy= 14 16.   Find the value using algebric formula i] 93x94     ii]  704 2 17.

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Prove that the sum of the squares of the diagonals of parallelogram is equal to the sum of the squares of its sides. Given that ABCD be a parallelogram. Construction : We have to Draw AF and DE perpendicular on side DC and on extended side AB to use Pythagoras theorem In ΔDEA, DE2 + EA2 = DA2 … (i) Similarly, In ΔDEB, DE2 + EB2 = DB2 DE2 + (EA + AB)2 = DB2 ( EB =EA + AB) DE2 + EA2 + AB2 + 2EA × AB == DB2 (DE2 + EA2) + AB2 + 2EA × AB = DB2 DA2 + AB2 + 2EA × AB = DB2 … (ii)( Using -----1) In ΔAFC, AC2 = AF2 + FC2 = AF2 + (DC − FD)2 = AF2 + DC2 + FD2 − 2DC × FD = (AF2 + FD2) + DC2 − 2DC × FD =AC2 = AD2 + DC2 − 2DC × FD ( using AD2 = AF2 + FD2)… (iii) Now,given that  ABCD is a parallelogram, AB = CD … (iv) And, BC = AD … (v) Look In ΔDEA and ΔADF, ∠DEA = ∠AFD (Both 90°) ∠EAD = ∠ADF (EA || DF -Alternate angles ) AD = AD (Common) ∴ ΔEAD cong. ΔFDA (AAS congruence criterion) ⇒ EA = DF … (vi) Adding equations (i) and (iii), we obtain DA2 +

OCCURRENCE OF METALS The earth’s crust is the major source of metals. Seawater also contains some soluble salts such as sodium chloride, magnesium chloride, etc. The elements or compounds, which occur naturally in the earth’s crust, are known as minerals. At some places, minerals contain a very high percentage of a particular metal and the metal can be profitably extracted from it. These minerals are called ores. Minerals:- The compounds of an element that occurs naturally in the earth’s crust. Ores: - The minerals from which an element can be profitably and conveniently extracted. Enrichment of ores: - It is done to remove earthy impurities like clay, sand etc. from an ore is called enrichment or concentration of the ore.  Gangue: - The earthy impurities that is found with ores. Extraction of Metals Extracting metal low in activity series:- The metals low in the reactive series are very less reactive. The oxides of such metals can be reduced to metals by heating alone e.g.  mercur