Indian civilization and culture                               भारतीय सभ्यता और संस्कृति

Chapter-1              ---by Mahatma Gandhi

Class- XII (English Literature) 

Idioms---Set-1

 1. Second to none 

= better than all others of the same kind

= the best

Example sentences

As a dancer, he is second to none.

The hotel offers a level of service that is second to none.

The group has a reputation that is second to none in the building industry.

Mom's chocolate cake is second to none.

Our scientific research is second to none. 

The city's public transportation system is second to none.

As a sportsman, Anil is second to none in this school.

As a teacher, Sanjeev Sir's sincerity and consistency towards learning is just second to none.

The reputation he has as a teacher was just second to none.

He was second to none in mathematics.

The philosophy of the Vendant and the Upnishads is second to none in the entire literature across the globe.

The service we received there in that restaurant during our stay in Patna was second to none.

The video quality of this phone is second to none.

2.back to square one

= in same situation, with no progress made.

= start all over again

= back to the beginning

=return to the starting point

Example sentences:

If this doesn't work, we are back to square one.

All of a sudden, I realized that I had rolled back to the square one.

We've got to get this done without going back to square one.

If they don't accept our proposal, we'll be back to square one.

In September, I could run 5 miles but I didn't exercise all winter and now I'm back to square one trying to run just one mile.

 Is knowledge free or do you think it sells? This is the question that many people are confused about. It is said that, in modern time, knowledge is something you have to pay for. The one who is from a wealthy family is more likely to get access to higher education. So, in this perspective knowledge seems to sell in today's world.

       Let me make it clear to you  that knowledge can never ever be free. Neither is it free today, nor ever had it been in olden times. Actually its price is something different than what we believe it to be. The price is not in the form of money or wealth. One has to pay what its price is. As a matter of fact, the price of knowledge is fixed and it has never ever changed since time immemorial. That particular price is curiosity as well as reverence towards knowledge. This is the real price that every ideal learner has to pay. Until and unless knowledge is treated as valuable and it is held in high esteem, it does not bless anyone. There's one and only one price of getting knowledge and that is to show curiosity towards it and feel the need to achieve it, and last not the least, one must show reverence towards the goddess of knowledge and the knowledge itself.

Notes by Dushyant Kumar

ELECTRICITY

Class X  

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                                        Electricity

↓

(as a subject)

The branch of physics that studies 

electric charge and the effects caused by it.

There are two types of electricity. 

 1)  Static electricity --- the study of charges at rest.

 2)  Current electricity ---- the study of charges in motion. Or, 

                                   A form of energy produced due to the flow of charges (electrons).

Electricity is a form of energy produced by the flow of charges through a conductor. It is a kind of energy that is easy to use and control. It powers our machines, vehicles, TV, bulbs, fans, computers and all other appliances. Modern way of life is fully dependent on electricity. 

CHARGE - Like mass, the charge is the fundamental property of matter. 

• Charge is possessed by fundamental particles of matter: electrons and protons.

• Electrons are called negatively charged particles.

• Protons are called positively charged particles.

There are two types of charges:

1. Positive charge

2. Negative charge

•  Unlike charges attract each other and like charges repel each other.

• In an atom, the number of electrons is equal to the number of protons. So, an atom is electrically neutral.

• When an atom or a material gains electrons, it becomes negatively charged. (How?)

• When an atom or a material loses electrons, it becomes positively charged. (How?)

There are some combinations of materials that when rubbed against each other, get charged. Like -----

1.  Glass rod -- silk cloth. : When rubbed, glass rod loses electrons and silk gains electrons.

• When two materials are rubbed and thus get charged, there is always the force of attraction between them because opposite charges are developed in them.

2. Ebonite rod -- wool

         When rubbed, ebonite rod gains electrons and so has excess of electrons and becomes -vely charged. On the other hand, wool loses electrons and so has an excess of protons and thus becomes +vely charged.

3. In case of plastic comb/pen - dry hair

When a plastic comb or pen is rubbed with dry hair, the plastic comb or pen gains electrons and becomes -vely charged. Since dry hair loses electrons, it becomes +vely charged.

 Due to the friction between two materials, there is a transfer of electrons and the materials get charged. The charges produced get confined to the materials (in insulators). This is what we call static electricity.

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The S.I. unit of charge is coulomb or C. It means charge is measured in coulomb like distance is measured in meters. The charge on an electron or proton is equal in magnitude but both are opposite in nature that’s why we put minus (-) sign to denote the charge on an electron.  Charge on ----

1e = -1.6 x 10-19C

1p = 1.6 x 10-19C

Let’s see how big 1 coulomb is i.e. how many electrons there are in 1C.

•    1.6 x 10-19C = 1e

•    1.6 x 10-19x 1C = 1e

•    1C = 1e/(1.6 x 10-19)

•    1C = (10/16) x 1019 e

•    1C = 6.25 x 1018e

Thus,  6.25 x 1018 electrons together make up 1C charge.

1 coulomb is the charge possessed by  6.25 x 1018 electrons.

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Another definition of 1 coulomb

1C is that much charge which exerts a force of 9 x 10-9 N on an equal charge placed at a distance of 1m from it.

 In other words, two 1C charges placed 1m apart from each other exerts a force of 9 x 10-9 N.

 But the question is how 1C charge is related to 9 x10-9 N force. For this, we need to learn Coulomb’s law.

COULOMB’S LAW

Statement: The force between any two charges is directly proportional to the product of the charges and inversely proportional to the square of the distance between them.

      

         

On combining the two equations, 

        Where, F = electrostatic force

                                         K = electrostatic constant

                                         K = 9 x 109 Nm2/C2

                                              (for vacuum or free space)

Now, if we take   q1 = 1C  ,     q2=1C  and  r = 1m

then,    F = 9 x 109 N ,  you can see this is a much stronger force.

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ELECTRIC CURRENT

 The flow of electric charge is known as electric current.

Electric current is carried by free electrons present in a conductor.

It is represented by the letter ‘I’. 

The rate of flow of electric charges is called electric current.

Or,

Electric current is the quantity of charge flowing per unit time through a conductor.

Let’s say, in time t s, Q amount of charge is flowing through a conductor.

          

                    The amount of charge flowing per unit time is called electric current I.

Thus, 

                                                   

 From the above formula of electric current, the unit of current is C/s. C/s is what is called ampere.

The S.I. unit of electric current is ampere represented by the letter A.

If we take I = 1A

                 Q = 1C

                                                       t = 1s ,     and put the values     in the formula

1A = 1C/ 1s 

• 1 A is the current when 1 C of charge is flowing through a conductor every 1 second.

1C = 1A x 1s

• When 1A of current is passing every 1s through a conductor, the amount of charge is 1C i.e.  6.25 x 1018 electrons are passing every second.

• Ammeter is the instrument used to measure electric current in a circuit.

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Thank You!

 

THE POWER OF A LENS = Class-X (Physics)

 Notes by Dushyant Kumar

Class- X

Physics

POWER OF A LENS

• The power of a lens is a measure of the degree by which it can bend light rays.

• If a lens can bend light rays more, it has more power. And if a lens can bend light rays less, it has less power.

• The power of a lens depends on its focal length.

• A convex lens is also called the converging lens. Because it has the power to converge light rays towards the principal axis at the principal focus.

• A convex lens has +ve focal length. So, its power is also +ve.

• A concave lens is also called the diverging lens. The reason is it has the power to diverge light rays away from the principal axis.

• A concave lens has -ve focal length. So, its power is -ve.

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More thickness  ↑                 Less thickness ↓

Less focal length ↓               Larger focal length ↑ 

More power ↑                       Less power ↓ 

The power of a lens is the reciprocal of its focal length in metres.

P= 1/f

          Where,   P =  power of the lens

f  = focal length (in metres)

If the focal length is given in cm, then first change it into m . Or,

Use this formula---- 

P = 100/f (cm)

• A lens of short focal length has more power.

• A lens of long focal length has less power.

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Power of combination of lenses

When you have more than one lens placed side by side, just add the powers of individual lenses to find the power of the combination.

P = P1 + P2 + P3 +....... 

The combination of lenses is used to increase the sharpness of the image free from the defects.

•   Be sure to put a proper sign before the value of the power of a lens. 

•  The power of a convex lens is always taken +ve. Like +1D, +2.5D, +2.0D etc.

•  The power of a concave lens is always taken -ve. Like -1D, -1.5D, -2.5D etc.

•  1 dioptre is the power of a lens whose focal length is 1 m.

•  Dioptremeter is the  instrument used to measure the power of a lens.

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