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When an n type semiconductor is joined to a p type semiconductor such that the crystal structure remains continuous at the boundary, the junction is called the p-n junction and the resulting combination is called a p-n junction diode or semiconductor diode.

At high temperature one half p-type semiconductor is mixed with the half n-type semiconductor such way p-n junction made. We know that electrons are majority carriers in n type semiconductors and holes or positive charges are majority carrier in p type semiconductors. So, p type portion contains positive charges majority carrier and n type portion has electrons as majority carrier at p-n junction.

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A pentavalent impurity like arsenic, phosphorous is added with pure semiconductor like silicon or germanium for making n type semiconductor. The most important requirement is that the size of the impurity atom should be nearly equal to the size of the atoms in the pure semiconductor silicon or germanium in this case. At a high temperature arsenic or antimony pentavalent atoms are added by special technology. The main structure of silicon or germanium should not be changed so the amount of impurity is controlled at the time of mixing rather these atoms are incorporated in the crystal lattice.

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Trivalent element like gallium or aluminum is mixed with pure semiconductor like silicon or germanium to make p type semiconductor. Three valence electrons of aluminum make bond with neighboring electrons of silicon. Here three covalent bonds are made. But the fourth bond is not completed. It is needed one electron to complete the bond. One electron of neibouring bond jumps into the vacancy and make a covalent bond with the vacancy. Now the bond is completed. A positively charge produces with covalent bond. In this way for each impurity atom accepts an election and a positive charge or hole produces in the semiconductor.

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The substances by which electricity or charges flow is called medium. It is classified into three types are

(i) Conductor,

(ii) Semiconductor

(iii) Non conductor

(i) Conductor: conductor is this substance in which electricity or charges can flow easily. Examples of conductors are copper, gold, iron etc metal, human body, acids, bases etc. through these substances charges can flow easily so they are conductors. Electrical conductivity of electricity conductors are also depends upon temperature. Conductivity of conductor in electricity decreases when temperature increases and conductivity increases when temperature decreases.

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Three types substances are mainly we have viz solid, liquid and gases. Solids are classified in three types according to electrical conductivities. This substances through electricity or charges can pass easily facing no prevention is called conductors. Conductors of electricity are silver, gold, iron, copper etc from metal. From these substances electricity cannot pass easily called insulators. The examples of insulators are rubber, mica, quartz, ceramics, glass ebonite etc.

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There are two types of electricity viz

  1. Current electricity
  2. Static electricity

Current electricity:  Electricity means charge. When the charge does not remain confined in one place, it moves one place to another place is called current electricity. We use current electricity in our house.

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 We use radio, television, refrigerators tube light etc in our home appliance. To operate these appliances we need electric energy. There are many kinds of sources of electrical energy like generator, electric cell or battery.

Let us consider a torch light. There are two or there dry cell in series combination is called battery. Copper plate and a small bulb connection with the battery. The source of energy in the torch light is battery because it supplies current here. Electric energy transfers from the battery to the bulb and the filament of the bulb heated and radiates light.

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Fiscal policy has powerful effects upon economic activity led to the Keynesian approach to macroeconomic policy which is the active use of government action to moderate business cycles.

Keynesian macroeconomics policies are

  1. First, the explicit dedication of macroeconomic policy instruments to real economic goals in particular full employment and real growth of National income.
  2. Second, Keynesian demand management is activist.
  3. Third, Keynesian has wished to put both fiscal and monetary policies in consistent and coordinated harness in the pursuit of macroeconomic objectives.