Physics X

Electricity

What is the history of Electricity?

The history of electricity is a complex and fascinating subject that spans several centuries. Here is a brief overview of some key milestones and developments in the history of electricity:

• Ancient Discoveries:

Ancient Greeks, such as Thales of Miletus, observed static electricity around 600 BCE. They noted that rubbing certain materials, like amber, could attract lightweight objects. Ancient Egyptians had knowledge of electric fish, such as the electric catfish, which could produce electric shocks.

• 18th Century:

Benjamin Franklin, an American polymath, conducted extensive experiments on electricity in the mid-18th century. He proposed the theory of positive and negative charges and famously flew a kite in a thunderstorm to demonstrate the connection between lightning and electricity. Luigi Galvani, an Italian physician, discovered in 1780 that the muscles of dissected frogs twitched when struck by a spark from an electrostatic machine. This observation led to the concept of "animal electricity" and laid the groundwork for the study of bioelectricity.

• 19th Century:

Alessandro Volta, an Italian physicist, invented the electric battery, known as the Voltaic pile, in 1800. This was the first reliable and continuous source of electric current. Michael Faraday, an English scientist, made significant contributions to the understanding of electricity and magnetism in the early to mid-19th century. He formulated the laws of electromagnetic induction and discovered electromagnetic rotations, paving the way for the development of electric motors and generators. Thomas Edison, an American inventor, and his team made numerous inventions and innovations in the late 19th century. Notably, Edison developed practical incandescent light bulbs and established the first electric power distribution systems, including the construction of the Pearl Street Station in New York City in 1882.

• 20th Century and Beyond:

What is the etymology of "Electricity"?

The word "electricity" is derived from the Latin word "electricus," which means "like amber" or "pertaining to amber." The Latin term itself is derived from the Greek word "ēlektron," which also refers to amber.

The association between amber and electricity dates back to ancient times. The ancient Greeks and Romans observed that when amber was rubbed with certain materials, it had the ability to attract lightweight objects like feathers. This phenomenon, known as static electricity, was later explained by the concept of electron transfer or the movement of charged particles.

The word "electricity" was first coined in English in the 17th century to describe the property or phenomenon of electrical attraction and repulsion. It gained popularity following the works of scientists like William Gilbert, who conducted extensive experiments and investigations into electrical phenomena during that time.

So, the term "electricity" ultimately derives from the Latin word "electricus," which was used to describe the properties of amber and its ability to exhibit electrical effects when rubbed.

The 20th century saw significant advancements in the understanding and application of electricity. Key developments included the invention of the vacuum tube, the discovery of electrons, the development of alternating current (AC) power systems, and the creation of integrated circuits, leading to the birth of modern electronics. The harnessing of electricity for various applications, such as transportation, communication, and industry, greatly transformed society. Electric power became more accessible and widespread, leading to the electrification of cities and the emergence of electrical appliances and devices. The 20th and 21st centuries also witnessed advancements in renewable energy technologies, such as solar power and wind power, as society sought more sustainable and environmentally friendly sources of electricity. The history of electricity is a rich and ongoing field of research and innovation, with countless contributions from scientists, inventors, and engineers across the centuries. It has had a profound impact on various aspects of human life and continues to shape the modern world.

What are some ancient Indian work on electricity?

In ancient India, there are a few references and works that touch upon the concepts related to electricity, although the understanding and application of electricity as we know it today were not present during that time. Here are a few examples:

Vedic Texts: The Vedas, which are ancient Hindu scriptures dating back to around 1500 BCE, contain mentions of phenomena that could be interpreted as electricity. For instance, the Rigveda mentions the presence of thunderstorms and lightning, which could be seen as an indirect reference to electrical phenomena.

Samudragupta Inscription: The Samudragupta inscription, dating back to the 4th century CE, mentions a machine known as the "yantra sarvasva" that produced light and sound. While the exact workings of this machine are unclear, it has been suggested by some researchers that it could have been a primitive form of an electric device or an early example of acoustic resonance.

Ancient Indian Scientists: Several ancient Indian scientists and scholars made significant contributions to the understanding of various scientific principles, although their work did not specifically focus on electricity. For example, Aryabhata, an astronomer and mathematician from the 5th century CE, developed mathematical models and techniques that laid the foundation for later developments in science and technology.

It's important to note that while these references exist, the ancient Indian understanding of electricity and electrical phenomena was limited compared to modern knowledge. The systematic study and application of electricity as a scientific discipline emerged much later in history.

Light

1. How do we see objects?

An object reflects light that falls on it. This reflected light, when received by our eyes, enables us to see things.

2. What are transparent media?

Those objects which allow light to pass through them. Some examples are air, glass, water, polythene sheet.

3. Why are we unable to see anything in a dark room?

We are unable to see anything in a dark room because there is an absence or lack of light. Light is essential for vision as it allows objects to reflect or emit light, which is then detected by our eyes. In a dark room, there is no or very little light to illuminate the objects around us. As a result, our eyes do not receive any light rays to form an image, and therefore, we perceive the space as dark and cannot see any objects present.

4. How are we able to see through a transparent medium?

We are able to see through a transparent medium because light can pass through it without significant absorption or reflection. A transparent medium refers to a substance that allows light to transmit through it with minimal obstruction or distortion.

5. What are some common phenomena associated with light?

Some common phenomena associated with light include:

Reflection: When light waves encounter a surface and bounce back, we observe the phenomenon of reflection. This is how we see our own reflection in a mirror or the reflection of light from other objects.

Refraction: Refraction occurs when light waves pass from one medium to another with a different optical density, causing them to change direction. This phenomenon is responsible for the bending of light when it passes through a prism or a lens.

Diffraction: Diffraction refers to the bending or spreading out of light waves as they encounter an obstacle or pass through a narrow opening. It is the reason why we observe patterns of light and dark bands when light passes through a narrow slit or around an object.

Interference: Interference occurs when two or more light waves overlap and either reinforce or cancel each other out. This phenomenon gives rise to patterns of light and dark regions, such as the colorful patterns observed in soap bubbles or thin films.

Dispersion: Dispersion refers to the separation of white light into its component colors when it passes through a prism or a medium with varying refractive indices. This is how we observe the beautiful colors of a rainbow.

Polarization: Polarization is the phenomenon in which light waves vibrate in a particular plane. Polarized light has its electric field oscillating in a specific direction, which can be filtered or selectively blocked using polarizing filters.

Scattering: Scattering occurs when light interacts with particles or molecules in the atmosphere, causing it to change direction and spread out in different directions. This is responsible for the blue color of the sky and the reddening of sunlight during sunrise and sunset.

Total Internal Reflection: Total internal reflection occurs when light waves traveling in a medium with a higher refractive index encounter a boundary with a medium of lower refractive index at an angle greater than the critical angle. The light is completely reflected back into the original medium, resulting in phenomena like fiber optics and mirages.

These are just a few examples of the fascinating phenomena associated with light. The study of these phenomena is part of the field of optics, which explores the behavior and properties of light.

NCERT Questions and Solutions

1. Which one of the following materials cannot be used to make a lens? (a) Water (b) Glass (c) Plastic (d) Clay

Ans: (d) Clay

Explanation : Clay is an opaque material and doesn't let light pass through it.

2. The image formed by a concave mirror is observed to be virtual, erect and larger than the object. Where should be the position of the object? (a) Between the principal focus and the centre of curvature (b) At the centre of curvature (c) Beyond the centre of curvature (d) Between the pole of the mirror and its principal focus.

Ans: (d) Between the pole of the mirror and its principal focus

Explanation : When the object is placed between the Focus and the Pole of a concave mirror the image formed is virtual, erect and enlarged.