Monday, October 20, 2014

CBSE Class 9 - Science - Gist on Work, Energy and Power

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Study Points

1. Work is said to be done if a force is applied on the object and it is displaced from its original position.

2. Three things are necessary for the performance of work:
  • There must be an applied force F.
  • There must be a displacement x.
  • The force must have a component along the displacement
3. The work done W by a force F on an object is
    W = Fd cos θ
    where d is the displacement of an object.
   
θ is the angle between the force and the displacement.

4
. If displacement is along the direction of work i.e. θ = 0°
    W = Fd


5. If displacement is opposite to the force i.e. θ = 180°
    W = -Fd

6. if the displacement is perpendicular to the force (i.e. θ = 90°), then work done is zero.

7. Work done on an object by a force would be zero if the displacement of the object is zero.

8. Work is a scalar quantity.

9. Unit of work is Joule (J).

10.  1 Joule = 1 newton × 1 metre = 1 Nm
11. One Joule of work is to be done on an object when a force of one newton displaces it by one metre along the time of action of the force.

Friday, October 17, 2014

CBSE Class 9: Science - CH3 - Gist on Atoms, Molecules and Ions

Atoms, Molecules and Ions

CBSE Class 9: Science - CH3 - Gist on Atoms, Molecules and Ions

Study Points


1. The law of conservation of mass states that there is no detectable loss or gain in total mass of the substances in a chemical reaction.

2. Law of Conservation of mass was proposed by the French chemist Antoine Lavoisier (1774)

3. The Law of constant proportion or definite proportions states that all pure specimens of the same compound contain the same elements combined together in the same proportion by weight.

4. Law of definite proportion was proposed by Louis Proust (1799).

5. An atom is the smallest particle of the element which can take part in chemical change and it can exist independently and retain all its chemical properties.

6. The smallest particle of matter made up of two or more atoms, which can exist in free state, is called a molecule.

7. Law of definite proportion does not hold good when the compound is obtained by using different isotopes of the combining elements .

8. Each atom of an element shows all the properties of the element.

Monday, October 13, 2014

CBSE Class 9/10 - PSA Quiz (English)

 PSA Quiz



Q1: In the following there are six sentences marked as A, B, P, Q, R, S. Positions of A and B are fixed. You are requested to choose one of the four alternatives which would be the most logical sequence of sentences in the passage.

A) The similarity between the human body and a machine is rather superficial.
B) The points of difference far outweigh the points of resemblance.
P) Beyond that comparison fails.
Q) No machine grows in size; no machine sees , hears  or feels.
R) It can be summed up in the statement  that both require  fuel and oxygen  and obtain energy.
S) No machine thinks.

(a) SQPR
(b) RPQS
(c) RPSQ
(d) QSPR

Directions: (Q2 - Q6): Identify the word whose spelling is correct.

Q2:
(a) Profesional
(b) Proffessional
(c) Proffesional
(d) Professional


Q3:
(a) Schdule
(b) Shidule
(c) Schdulle
(d) Schdule

Q4:
(a) Intelligence
(b) Intilligence
(c) Intalligence
(d) Intelligance

Q5:
(a) asshaimed
(b) ashamid
(c) ashimed
(d) ashamed

Thursday, October 9, 2014

CBSE Class 9 - Maths - Quadrilaterals (NCERT Ex 8.2)

Quadrilaterals
NCERT Ex 8.2


Q1: ABCD is a quadrilateral in which P, Q, R and S are mid-points of the sides AB, BC, CD and DA (see the given figure). AC is a diagonal. Show that:



(i) SR || AC and SR = AC

(ii)PQ = SR

(iii)PQRS is a parallelogram.


Answer:

(i) In ▲ADC, S and R are the mid-points of sides AD and CD respectively.

In a triangle, the line segment joining the mid-points of any two sides of the triangle is parallel to the third side and is half of it.

∴ SR || AC and SR = AC ... (1)

(ii) In ▲ABC, P and Q are mid-points of sides AB and BC respectively. Therefore, by using mid-point theorem,

PQ || AC and PQ = AC ... (2)

Using equations (1) and (2), we obtain

PQ || SR and PQ = SR ... (3)

⇒ PQ = SR

(iii) From equation (3), we obtained

PQ || SR and PQ = SR

Clearly, one pair of opposite sides of quadrilateral PQRS is parallel and equal.

Hence, PQRS is a parallelogram.


Q2: ABCD is a rhombus and P, Q, R and S are the mid-points of the sides AB, BC, CD and DA respectively. Show that the quadrilateral PQRS is a rectangle.

Answer:



In ▲ABC, P and Q are the mid-points of sides AB and BC respectively.

∴ PQ || AC and PQ = AC (Using mid-point theorem) ... (1)

Saturday, October 4, 2014

CBSE Class 9 - Science - CH4 - Gist on Structure of The Atom

Structure of The Atom


Study Points

  1. Democritus, Greek Philosopher in 400 BC named the smallest piece of matter “ATOMOS ,” meaning “not to be cut.”
  2. Dalton's theory (1803) was based on the premise that the atoms of different elements could be distinguished by differences in their weights.
  3. WIth the invention of Scanning Tunneling Microscope we can see atoms.
  4. Electrons, protons and neutrons are the fundamental particles of an atom.
  5. Electrons were discovered by JJ Thomson in discharge tube experiments as cathode rays.
  6. Cathode rays are streams of negatively charged particles.
  7. They are deflected by electric and magnetic fields.
  8. The specific charge of electron was determined by J. J. Thomson
  9. The charge of the electron is 1.602 x 10-19 coulombs.
  10. The absolute mass of electron is 9.108 x 10-28 g or 9.108 x 10-31kg
  11. Protons are positive rays that were discovered by Goldstein in the discharge tube experiments when perforated metal cathode was used.

Tuesday, September 30, 2014

CBSE Class 11 - 12 English Grammar - Official Sentences

Official Sentences

Following sentences or phrases are commonly used for official or administrative work.


  1. Arrangements are being made to ensure timely submission of reports.
  2. Administrative approval may be obtained.
  3. Competent authority's sanction is necessary.
  4. Concurrence of the finance branch is necessary.
  5. Exigencies of administrative work.
  6. Explanation from the defaulter may be obtained.
  7. His request be acceded to.
  8. In anticipation of your approval.
  9. Such action may be deemed necessary.
  10. Repugnant to the context.
  11. Show cause as to why such action should not be taken.
  12. The file in question is not traceable.
  13. Timely compliance may be ensured.

Saturday, September 27, 2014

CBSE Class 7 - Science - CH3 - Fibre to Fabric (MCQs)

 Fibre to Fabric 
(MCQs)

Q1: Which of the following is NOT a Vegetable fibre?

(a) flax
(b) silk
(c) hemp
(d) jute

Q2: Vegetable fibres are made up of

(a) cellulose
(b) protein
(c) nylon
(d) rayon

Q3: Animal Fibres are made up of

(a) cellulose
(b) protein
(c) nylon
(d) rayon


Q4:  Which of the following process is NOT part of wool extraction?