HTML.

HTML (Hyper Text Markup Language) is text markup language used to create HTML documents (Web Pages) for The Internet. HTML is a set of logical codes or tags (markup) that are used to define the Web browser how to present the information in the Web page. It can be applied and embedded in the text to add formatting, linking that constitute the appearance of the Web documents and the information. It is interpreted by the Web browser. The Web browser is software that runs on the Web client (user computer ) and it interprets HTML tags to display the contents of the Web page. Source: HTML is platform independent language. It is not a programming language like C, C++, java and BASIC. Basically, it is a set of markup tags that tells the browser how to display the Web page content. Some popular markup languages are DHTML, SGML (Standard Generalized Markup Language), XHTML (Extended HTML),XML (Extensible Markup Language), etc. Tim Berners Lee developed HTML in 1990, at CERN (Conseil Europeenne pour la Recherche Nucleaire ), the European Particle Physics Laboratory in Geneva, Switzerland. There are different versions of HTML; these are HTML, HTML+, HTML 1.0, HTML 2.0, HTML 3.2, HTML 4.01 (It has accessibility of Cascading Style sheet, and Multimedia) and now HTML 5.0 ( It has accessibility of local storage and offline database). Uses of HTML It is used for basic layout creating or designing the Web page. Without HTML, the World Wide Web will not exist. It allows embedding text, image, multimedia (audio / video) and links to other documents and the Web pages. It provides a means to create structured document by using paragraph, character formatting, links and lists. It can embed scripts such as CSS, JavaScript, which affect the behavior and design of the Web page. Advantages of using HTML It is highly flexible and user-friendly. It is an open technology that supports almost all the Web browser and platforms like MS-Windows, Macintosh, UNIS, etc. It is efficient and reliable. You can create the Web page in order to advertise and promote products and services. It is easily understandable and does not require long time training. It provides search engine compatible to the Web sites. Disadvantages of using HTML It is complex to design attractive Web page only using HTML. So, other languages are used for additional programming. It is difficult to develop a complete Web Site by using only HTML. Web development tools like Dreamweaver, Foundation are used. It cannot be used to develop a dynamic Web page. There is no any complete acceptable standard of HTML. There are many incompatibilities of HTML. HTML Tags HTML is made up of different tags and attributes. The tag is an HTML command that shows the layout or displays the desired output of a whole or part of the Web page. HTML tag is bound by angular brackets ( < > ) that always opens with a < (less than ) sign and closes with a > (greater than) sign. It controls the appearance, layout and flow of the Web page. A tag contains three parts: element (identification of tag), attribute and value. The basic structure of tag is: text e.g. Computer Here, is the beginning tag and is the ending tag. HTML tags can be of two types: Paired Tags Singular Tags 1. Paired Tags It is also called container tag. A tag is said to a paired tag if it along with a companion tag or closing tag appears at the end. For example, the tag is paired tag. The tag with its closing tag is used to rendered in Bold Text. In paired tag, first tag is called the opening tag and the second tag is called the closing tag. 2. Singular Tags The second type of tag is the singular tag, which is also known as a stand-alone tag or empty tag. The stand-alone tag does not have companion tag or closing tag. For example : Other singular tags are: Tags Description
Insert a link break

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Defines a horizontal rule <!--> Defines a comment Meta Tag The Meta tag is one of the head elements. Meta tag is used to make the Website or its content searchable on the WWW or internet. This tag offers information about page or description about page or author of page or keyword that is relevant to that page. Actually, it is used for search engine information. The search engine interacts with the Meta tag of the HTML page at first. Basic Structure of HTML Document The HTML document is mainly divided into two sections. They are: Head section and Body section. Head section is used as the first tag of any web page which signifies that it is beginning of web page.It has some elements that define header materials. It gives a descriptive title to a document. The HTML 4.0 for many good reasons requires a use of the tag. Titles show up in browser windows title bars and in bookmark and history listings. In each of these cases, one provides an important reader service when one specifies a title because the browser will display just the document’s URL. The remaining HTML elements are contained within. Here’s the example of basic structure of HTML This is the Body of the Webpage.

Snell's law

Derivation from Fermat's principle[edit]

Snell's law can be derived from Fermat's principle, which states that the light travels the path which takes the least time. By taking the derivative of the optical path length, the stationary point is found giving the path taken by the light (though the result does not show light taking the least time path, but rather one that is stationary with respect to small variations as there are cases where light actually takes the greatest time path, as in a spherical mirror). In a classic analogy, the area of lower refractive index is replaced by a beach, the area of higher refractive index by the sea, and the fastest way for a rescuer on the beach to get to a drowning person in the sea is to run along a path that follows Snell's law.

Light from medium 1, point Q, enters medium 2, refraction occurs, and reaches point P finally.

As shown in the figure to the right, assume the refractive index of medium 1 and medium 2 are ${\displaystyle n_{1}}$ and ${\displaystyle n_{2}}$ respectively. Light enters medium 2 from medium 1 via point O.

${\displaystyle \theta _{1}}$ is the angle of incidence, ${\displaystyle \theta _{2}}$ is the angle of refraction.

The traveling velocities of light in medium 1 and medium 2 are

${\displaystyle v_{1}=c/n_{1}}$ and

${\displaystyle v_{2}=c/n_{2}}$ respectively.

${\displaystyle c}$ is the speed of light in vacuum.

Let T be the time required for the light to travel from point Q to point P.

${\displaystyle T={\frac {\sqrt {x^{2}+a^{2}}}{v_{1}}}+{\frac {\sqrt {b^{2}+(l-x)^{2}}}{v_{2}}}={\frac {\sqrt {x^{2}+a^{2}}}{v_{1}}}+{\frac {\sqrt {b^{2}+l^{2}-2lx+x^{2}}}{v_{2}}}}$

To minimize it, one can differentiate :

${\displaystyle {\frac {dT}{dx}}={\frac {x}{v_{1}{\sqrt {x^{2}+a^{2}}}}}+{\frac {-(l-x)}{v_{2}{\sqrt {(l-x)^{2}+b^{2}}}}}=0}$ (stationary point)

Note that ${\displaystyle {\frac {x}{\sqrt {x^{2}+a^{2}}}}=\sin \theta _{1}}$

and ${\displaystyle {\frac {l-x}{\sqrt {(l-x)^{2}+b^{2}}}}=\sin \theta _{2}}$

Therefore,

${\displaystyle {\frac {dT}{dx}}={\frac {\sin \theta _{1}}{v_{1}}}-{\frac {\sin \theta _{2}}{v_{2}}}=0}$

${\displaystyle {\frac {\sin \theta _{1}}{v_{1}}}={\frac {\sin \theta _{2}}{v_{2}}}}$

${\displaystyle {\frac {n_{1}\sin \theta _{1}}{c}}={\frac {n_{2}\sin \theta _{2}}{c}}}$

${\displaystyle n_{1}\sin \theta _{1}=n_{2}\sin \theta _{2}}$

15.Impact and Non-Impact printer

Printers
Impact and Non-Impact Printers are two categories of the printer. Impact printers
involve mechanical components for conducting printing. While in Non-Impact printers,
no mechanical moving component is used.

Impact Printers:
It is a type of printer that works by direct contact of an ink ribbon with paper. These
printers are typically loud but remain in use today because of their unique ability to
function with multi part forms. An impact printer has mechanisms resembling those of
a typewriter.
Example of Impact Printers, Dot-matrix printers, Daisy-wheel printers, and line printers.

Non-Impact Printers:
It is a type of printer that does not hit or impact a ribbon to print. They used laser,
xerographic, electrostatic, chemical and ink jet technologies. Non-impact printers are
generally much quieter. They are less likely to need maintenance or repairs than earlier
impact printers.
Example of Non-Impact Printers is Ink jet printers and Laser printers.

14.Why are lithium compounds soluble in organic solvents?

Ans.Due to high polarizing power, there is increased covalent character of lithium
compounds which is responsible for their solubility in organic solvents

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13.Name the anomalous properties of lithium.

Ans. The anomalous behaviours of lithium is due to the following-

(i) Exceptionally small size of its atom and ion., Li+

(ii) High polarizing power (I, e; charge / radius radio)

12..Why is sodium hydrogen carbonate known as baking powder?

Ans.Sodium hydrogen carbonate is known as baking soda because it decomposes on heating

to generate bubbles of CO2 (leaving holes in cakes and bread)

11.Explain how a plane mirror can form a real image.

The image formed by a plane mirror is always virtual (meaning that the light rays do not actually come from the image), upright, and of the same shape and size as the object it is reflecting. A virtual image is a copy of an object formed at the location from which the light rays appear to come.