### What are the negative effects of using chemicals?

What are the negative effects of using chemicals? Chemicals are used for different experiments in chemistry. But they can be harmful to humans and the environment when they are not properly used. i) Chemicals are used to keep fish and meat fresh and ripen fruits which is harmful to health. ii) Preservatives are used to preserve different food products which are risky for health. iii) Excessive use of chemical fertilizer harms plants. iv) Different harmful substances enter our bodies through blood by using artificial cosmetics, colors, etc. You may like What is Electrocardiograph? What is biological currency? What is activation energy? What is rate of reaction? What is green chemistry?

## Semiconductor and Electronics Notes for Class 11 - 12

Learning Outcomes

• Explain band theory of solid materials
• Explain conductor, non-conductor, and semiconductor by band theory
• Explain intrinsic and extrinsic semiconductors
• Explain the concept of electron and hole in semiconductors
• Explain the p-type and n-type semiconductor
• Explain the construction and function of the junction diode
• Explain rectification
• Explain the construction and function of a junction transistor
• Explain the use of transistor as amplifier and switch
• Explain conversion of a different number system
• Explain Binary operation
• Analysis of the program of different logic gate

## Explain band theory of solid materials

Energy Band: There is a slight difference in the energy of electrons revolving in the same orbit in an atom of any matter. The range between the maximum and minimum energy level of these electrons situated in the same orbit is called the energy band. The energy level and energy band are not the same. The energy level is the orbit, where electrons rotating revolves with specific energy around the nucleus, of atoms in matter. The energy band is the energy range of electrons in the same orbit in different atoms of matter.

The main three energy bands of solid are -

a) Valence band; b) Conduction band; c) Forbidden energy band.

a) Valence Band: The electron in the outermost shell of an atom is called the valence electron. The range of energy of Valence electrons is called the valence band. The valence band in Insert gas is completely filled.

b) Conduction Band: Free valence electron in atom takes part in conducting current. The energy-range electron is called the valence band. All electrons in the conduction band are free electrons. In an insulator, the conduction band is empty. So, no electric current passes through the conduction band of the insulator.

c) Forbidden Energy Band or Gap: The range of energy between the valence band and conduction band is known as the forbidden energy gap. No electron can stay in the forbidden energy band because of the absence of an authorized energy level. In order to transfer an electron from the valence band to the conduction band, external energy which is equal to the forbidden energy gap is required.

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Semiconductor

The substances whose electric conductivity is less than conductor but greater than insulators and their resistances decrease with the increase of temperature and their electric conduction property changes remarkably due to dropping necessary impurity are called band theory.

Band Theory

On the basis of the forbidden energy gap between the valence band and conduction bands, solid materials can be classified as conductor, non-conductor, and semi-conductor. The theory by which the electric conductivity of a substance is described is called band theory.

Doping

The process of adding a very small amount of selected impurity to an intrinsic semiconductor is called doping.

Forward bias

When the positive and negative terminals of a battery are connected to the p-side and n-side of a diode respectively, the diode is said to be reverse biased.

Solar battery

p-n junction device made of silicon that converts solar energy to electrical energy is called a solar battery.

Amplifier

The device that amplifies the input signal in output, is called an amplifier.

Logic gate

Circuits that are used to process digital signals are called logic gates.

Universal gate

The gate by which basic can be constructed is called the universal gate.