In optics, the corpuscular theory of light, arguably set forward by Descartes in 1637, states that light is made up of small discrete particles called "corpuscles" which travel in a straight line with a finite velocity and possess impetus. This was based on an alternate description of atomism of the time period. The model of light and the particle model of light, which together describe the wave-particle duality in which light is understood to possess both wave and particle functions. The wave theory and the particle theory of light were long considered to be at odds with one another.

Huygens’ wave theory of light: In 1678, Dutch physicist Christian Huygens proposed a theory to explain the wave nature of light. This theory is called Huygens’ wave theory of light. According to wave theory of light, a source of light sends out disturbance in all directions. When these waves carrying energy reach the eye, they excite the optic nerves and the sensation of vision is produced. Main postulates of Huygens’ wave theory:
i. Light energy from a source is propagated in the form of waves: The particles of the medium vibrate about their mean positions in the form of simple harmonic motion. Thus, the particles transfer energy from one particle to its neighbouring particle and reach the observer.
ii. In homogeneous isotropic medium, the velocity of wave remains constant: Speed of the wave is not affected because density and temperature of isotropic medium are same throughout.
iii. Different colours of light waves are due to different wavelengths of light waves: Each wave has its own wavelength. As the wavelength changes, its colour and frequency also changes. This is indicated by change in the colour.
iv. The material medium is necessary for the propagation of wave: Periodic disturbance is created in the medium at one place which is propagated from that place to another place. The medium only carries disturbance and hand it over to the next particle. To explain the propagation of light waves through vacuum, Huygens suggested the existence of a hypothetical medium called ‘luminiferous ether’.

Sodium and Potassium are the two metals which can be cut with a knife.

given,
a₂=14 
a₃=18 
d=a₃−a₂=4 
a₁=a₂−d 
a1 =14-4
a=10
Sn=n/2(2a+(n-1)d)
 Sn=51/2(2*10+(51-1)4)
 Sn=5610

The interests of people can slow down and economy if people do things like boycotting, teachers in walk outs different situations can cause the economy to drop not having the right amount of people to do the job they need them to. 

The average size of holdings for 'all sizes' at all India level had shown a steady decline over all the censuses, while in 1970-71 it was 2.28 hectares, it came down to 2.00 hectares in 1976-77, 1.84 hectares in 1980-81, 1.69 hectares in 1985-86, 1.55 hectares in 1990-91, which further reduced to 1.41 hectares

A force is a push or pull upon an object resulting from the object's interaction with another object. Whenever there is an interaction between two objects, there is a force upon each of the objects. There are many examples of forces in our everyday lives: weight force (i.e. the weight of something) the force of a bat on the ball. the force of the hair brush on hair when it is being brushed. A force is a push or pull acting upon an object as a result of its interaction with another object. ... Previously in this lesson, a variety of force types were placed into two broad category headings on the basis of whether the force resulted from the contact or non-contact of the two interacting objects.

Huynh Phu so was the founder of the movement named Hoa-Hao in Indo China. He performed miracles and helped the poor. His criticism against useless expenditure had wide appeal. He opposed the sale of child brides, gambling and the use of alcohol and opium. The French tried to suppress the movement inspired by him. They declared him mad and put him in a mental asylum. He was exiled to Laos. His followers were also arrested and placed in concentration camps.

Note : the nationalist movement in indo-china is deleted by cbse. it is not in syllabus

संदेश लेखन का प्रारूप (Format for Message Writing)

 (1) औपचारिक संदेश लेखन का प्रारूप (Format For Formal Message Writing)

                            संदेश

दिनांक : …….                          समय : ……

संबोधन ………

विषय (जिस विषय हेतु सन्देश दे रहे हैं )………………………………………..

………………………………………………………………………………………………

…………………………………..

अपना नाम 

(2)   अनौपचारिक संदेश लेखन का प्रारूप (Format For Informal Message Writing)

                           संदेश

दिनांक : …….                          समय : ……

विषय (जिस विषय हेतु सन्देश दे रहे हैं , वो लिखें )

…………………………………………………………….

…………………………………………………………….

और अपना  नाम 

संदेश लेखन के कुछ उदाहरण 

अनौपचारिक संदेश व औपचारिक संदेश लेखन के कुछ उदाहरण (Example of Formal and Informal Message Writing)

उदाहरण – 1 

गणतंत्र दिवस के शुभ अवसर पर देशवासियों के लिए एक संदेश लिखें। 

Ohm’s Law

George Simon ohm(in 1826)studied relationship between I and V across the ends of conductor.

Ohm’s Law states that electric current flowing in a conductor is directly proportional to potential difference across the ends of the conductor,provided temperature and other physical conditions remains constant.

V=IR

R=Resistance of conductor

Resistance of a conductor is the property of conductor to oppose the flow of charge through it.

R = V/I

Unit of resistance is ohm

1 ohm =  1 Volt / 1 Ampere

Resistance of a conductor is said to be 1 ohm if a potential difference of 1 volts across the ends of conductor makes a current of 1 ampere to flow through it.

Slope = I / V

Slope of graph V and I=Resistance of a conductor

V=IR

I= V/R

If R is halved then I is doubled.

If R is doubled then I is halved.

Electric potential at a point in an Electric field (for instance, let's take it as uniform) is the amount of work done in moving a unit positive charge from infinity to that point against electric forces. (attraction or repulsion)

whereas Electric potential difference between two points in an Electric field is defined as the amount of work done in moving unit positive charge from one point to another point against the electric force.

In other words, Potential difference is simply the difference of scalar potentials between two points or anything you consider...

Now let's take an example.

Say, you're placing a charge (+q) at the point O. Also, There are two points A & B in the electric field E(It acts outward since the line charge is positive). Now, you want to move a charge (say +q) from B to A. Then, you've to do some work against the force of repulsion. This work done is the potential difference between two points or Voltage (i.e.) WB?A=dV which further equals ?E.dx. Electric field is simply the force experienced by unit positive charge.

If you bring the same charge from ? instead of B, it's electric potential. Using the above figure & integrating for total work done (with limits ? to some scalar distance r), one could derive Electric potential at a point. It's given by V=q4??r. But, you could ask, "Why this work is not stored as some potential energy?"

Yes, It is. But, Potential energy requires the magnitude of another charge also... If r is the distance of separation of two charges, P.E. is given by Ep=qQ4??r. In other words, Ep=VQ

1. Regeneration means the regrowth of a damaged or missing organ part from the remaining tissue. As adults, humans can regenerate some organs, such as the liver. If part of the liver is lost by disease or injury, the liver grows back to its original size, though not its original shape.

2. Budding is a type of asexual reproduction in which there is a continuous regeneration of cells at one specific site on the body of an organism. A bud grows as an outgrowth on that site.

3. 

• The cutting, layering and grafting are all the methods of vegetative propagation.
• The vegetative propagation is the process through which the progeny plants develop from the parent plant.
• The cutting process involves the cutting of the stem part of the plant and grown in the soil, the stem develops roots and leaves and new plants are grown through this way.
• The layering process occurs when from the same parent stem many branches develop each stem develop a root system and live as an individual plant.
• The grafting is the process through which a stem is cut and tied over other plant stem this way the quality of both plants will retain in a single plant.

Tissue culture is a technique of developing an organ or tissue in a laboratory using fragments of tissues and organs, on a nutrient media for proper development.

Factors responsible for the location in the Hugli basin are:
(i) Nearness of the jute producing areas.
(ii) Low-cost water transport, supported by a good network of railways, roadways and waterways to help the movement of raw material to the mills.
(iii) Abundant water for processing raw jute.
(iv) Cheap labour from West Bengal and adjoining states of Bihar, Orissa and Uttar Pradesh.
(v) Kolkata as an urban centre provides banking, insurance and port facilities for export of jute goods.

The reaction between calcium oxide (CaO) and water (H2O) to form calcium hydroxide Ca(OH)2 is an exothermic combination reaction.

This is because: Calcium oxide reacts with water to form slaked lime Ca(OH)2 which means the oxides of calcium combine with molecules of free molecules of O- and H+

This reaction generates a lot of heat accompanied with hissing sound and thus is stated to be exothermic.

Human development index (HDI) is a better indicator than per captia income for many reasons :

1.Any increase in the per captia income can be due to the use modern capital

intensive technology which is labour displacing in nature and thus adversely affecting the poor.

2.Per captia income ignores non material things like happiness index security health  literarcy rate etc. though they may be more important for a human it is not a reliable source of economic index.more over the distribution of the per captia income makes the rich richer and poor poorer

On the other hand human development index (HDI) computes all the things essential for a development of a country rather than focusing only on economic aspect  

Globalisation is defined as the integration between countries through foreign trade and foreign investments by multinational corporations (MNCs). Increase in foreign trade, migration of people from one country to another, the flow of capital finance from one country to another and private and public investments from foreign countries all together contribute to globalisation.