UKPCS Science: Conductors, semiconductors and insulators(3) #33

Oracle IAS, the best coaching institute for UPSC/IAS/PCS preparation in Dehradun brings to you UKPCS Science (paper #6).

Semiconductor p-n junction diode

If a crystal of p-type material is joined to a crystal of n-type material a p-n junction forms.

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UKPCS Science: Conductors, semiconductors and insulators(2) #32

Oracle IAS, the best coaching institute for UPSC/IAS/PCS preparation in Dehradun brings to you UKPCS Science (paper #6).

Semiconductor materials

Elements that are used as semiconductors, such as silicon and germanium, have four outer shell electrons. This means that they can form four bonds with other identical atoms.

In a crystal of pure silicon each silicon atom is surrounded by four other silicon atoms. In this state the silicon will not conduct.

Pure silicon can be doped by tiny quantities of impurities by diffusing the impurities as a gas into the liquid semiconductor before it crystallizes. If an impurity element with five outer shell electrons, such as arsenic, is added to silicon in small quantities, (approximately one impurity atom to every one million silicon atoms), the impurity atoms will fit into the crystal structure but there will be one electron not bonded into the valence band of the crystal. This free electron is a charge carrier able to move within the conduction band.

This impurity causes the material to conduct and is called n-typesilicon.

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UKPCS Science: Conductors, semiconductors and insulators(1) #31

Oracle IAS, the best coaching institute for UPSC/IAS/PCS preparation in Dehradun brings to you UKPCS Science (paper #6).

Classifying materials

Materials can be placed into three groups according to their electrical resistance:

  • conductors
  • semiconductors
  • insulators

Insulators and pure semiconductors have a very high resistance, while conductors have a very low resistance. This difference in conduction is explained by electron bands.

Band theory of conduction Continue reading “UKPCS Science: Conductors, semiconductors and insulators(1) #31”

UKPCS Science: Telescope #30

Oracle IAS, the best coaching institute for UPSC/IAS/PCS preparation in Dehradun brings to you UKPCS Science (paper #6).

A telescope is an important tool for astronomy that gathers light and directs it to a single point. Some do this with curved mirrors, some with curved lenses, and some with both. Telescopes make faraway things look bigger, brighter and closer. Galileo was the first person to use a telescope for astronomy, but he did not invent them. The first telescope was invented in the Netherlands in 1608. Some telescopes, not mainly used for astronomy, are binoculars, camera lenses, or spyglasses.

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UKPCS Science: Microscope #29

Oracle IAS, the best coaching institute for UPSC/IAS/PCS preparation in Dehradun brings to you UKPCS Science (paper #6).

A microscope is a scientific instrument. It makes things normally too small to be seen look larger. This way they can be seen better and examined correctly. People who use microscopes commonly in their jobs include doctors and scientists. Microscopes are commonly used in schools to help students in science classes such as biology or chemistry.

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UKPCS Science: Human Eye(3) #28

Oracle IAS, the best coaching institute for UPSC/IAS/PCS preparation in Dehradun brings to you UKPCS Science (paper #6).

Defects of vision and their corrections:

There are three common defects of vision. They are:

1) Myopia (Short-sightedness or Near-sightedness)

2) Hypermetropia (Long-sightedness or Far-sightedness)

3) Presbyopia

Myopia Continue reading “UKPCS Science: Human Eye(3) #28”

UKPCS Science: Human Eye(2) #27

Oracle IAS, the best coaching institute for UPSC/IAS/PCS preparation in Dehradun brings to you UKPCS Science (paper #6).

Working of the Eye

The light rays coming from the object enter the eyes through pupil and falls on eye lens. The eye lens then converge the light rays and produce an image of the object on retina which is real and inverted. Retina has large number of light sensitive cells which can generate electrical signals. After the image is formed on the retina it sends electrical signals to the brain and we have a sensation of image. Also, even though the image formed on retina is inverted out mind interprets it as erect.

So, eye lens is the convex lens and retina is the screen of the eye. Continue reading “UKPCS Science: Human Eye(2) #27”

UKPCS Science: Human Eye(1) #26

Oracle IAS, the best coaching institute for UPSC/IAS/PCS preparation in Dehradun brings to you UKPCS Science (paper #6).

Parts of eye:

Sclera: The knowledge of eye parts and functions is both useful and interesting. The white part of our eyes is known as sclera. It consists of fibrous tissues. The job of this part it to protect the internal parts of the eye.

Cornea: The transparent tissue through which light enters the eyes is called cornea. It exists in front of the eye. That is why, it looks prominent among different parts of the human eye.

Iris: Iris is made up of muscles which contract or relax in order to adjust the amount of light which enters the eye.

Pupil: There are many interesting facts about the pupil. It is, actually, an aperture controlled by the iris muscles. For instance, when it is dark, the iris muscles relax, causing the pupil to open up wider. Therefore, more light enters the eyes to enable us to see better. On the other hand, the pupil becomes narrow due to the contraction of the iris muscles. It occurs in the presence of excessive light in order to protect the cells of the eyes.

Lens: The lens is present behind the pupil. Light enters the pupil, passes through the lens and is focused on the retina of the eye. The lens is capable of changing its shape in order to help us see near or far off objects. This is about how the human eye works.

Retina: Digging further deeper into the human eye anatomy, you will come across the retina. The retina converts light into electrical signals which are transferred to the brain for processing. The retina contains two types of cells: rods and cones. These cells are sensitive to light. Rods are important for night-time vision when there is little light. On the other hand, cones play an important role in helping us see colors.

Optic Nerve: The optic nerve takes electrical signals from the retina of the eye to the brain.

The Human eye works on the refraction of light through a natural convex lens made up of transparent living material and enables us to see things around us. And the ability to see is called vision, eyesight or drishti. Human eye consists of cornea, iris, pupil, ciliary muscles, eye lens, retina and optical nerve.

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UKPCS Science: Electrical safety #25

Oracle IAS, the best coaching institute for UPSC/IAS/PCS preparation in Dehradun brings to you UKPCS Science (paper #6).

Electricity can be hazardous. Insulation, earthing, fuses and circuit breakers help to protect us from electrical injury. Electrical energy is current multiplied by voltage and time.

  • Insulators are used in electrical equipment to support and separate electrical conductors without allowing current through themselves. Glass, plastic, rubber, air, and wood are used as insulator. They form part of covering of copper wire and restrict the appliance from becoming live.
  • Earthing: It is a part of electrical circuit which is done on initial level in order to connect the electrical system with mass of earth so as to have discharge the electrical energy.

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UKPCS Science: Electrical/power grid #24

Oracle IAS, the best coaching institute for UPSC/IAS/PCS preparation in Dehradun brings to you UKPCS Science (paper #6).

An electrical/power grid is an interconnected network for delivering electricity from suppliers to consumers. It consists of generating stations that produce electrical power, high voltage transmission lines that carry power from distant sources to demand centers, and distribution lines that connect individual customers.

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