Carbon Transmitter

Carbon Transmitters are used in telephone handset. It is constructed by placing carbon granules between metal plates known as electrodes. One of the metal plates is a thin diaphgram. It takes vibrations in pressure caused by sound waves and transmits these vibrations to the carbon granules.

The vibrations produced give pressure to carbon grains. As a result of it, the electric current flows through the grains and copies the voice. The electric copy of the person’s voice, who has called up flows through a wire , producing vibrations in the magnetic field of an electromagnet.

Due to the vibrations, permanent magnet vibrates a diaphgram which generates sounds similar to the caller’s voice. Through Alexander Grahem Bell, a Scottish inventor invented telephone, it was Thomas Edison who introduced carbon transmitter and thus improved upon Grahams Bells Telephone.

Zener diode as voltage regulator

When the ac input voltage of a rectifier fluctuates, its rectified output also fluctuates.To get a constant dc voltage from the dc unregulated output of a rectifier, we use a zener diode. The circuit diagram of a voltage regulator using a zener diode is shown in Fig.1

The unregulated dc voltage (filtered output of a rectifier) is connected to the zener diode through a series resistance Rs such that the zener diode is reverse biased.If the input voltage increases, the current through Rs and zener diode also increases.This increases the voltage drop across Rs without any change in the voltage across the zener diode.This is because in the breakdown region, zener voltage remains constant eventhough the current through the zener diode changes.Similarly, if the input voltage decreases, the current through Rs and zener diode also decreases.The voltage drop across Rs decreases without any change in the voltage across the zener diode.Thus any incease/decrease in the input voltage results in, increase/decrease of the voltage drop across Rs without any change in voltage across the zener diode.Thus the zener diode acts as a voltage regulator.We have to select the zener diode according to the required output voltage and accordingly the series resistance Rs.

p-n junction diode under forward bias

When an external voltage V is applied across a semiconductor diode such that p-side is connected to the positive terminal of the battery and n-side to the negative terminal[Fig. 1.1(a)],it is said to be forward biased.

Fig.1.1(a)

The applied voltage mostly drops across the depletion region and the voltage drop across the p-side and n-side of the junction is negligible.(This is because the resisitance of the depletion region-a region where there are no charges-is very high compared to the resistance of n-side and p-side). The direction of the applied voltage[V] is opposite to the built-in potential V0.As a result,the depletion layer width decreases and the barrier height is reduced [Fig. 1.1(b)].The effective barrier height under forward bias is [V0-V].

Fig.1.1(b)

If the applied voltage is small, the barrier potential will be reduced only slightly below the equilibrium value, and only a small number of carriers in the material-those that happen to be in the uppermost energy levels-will possess enough energy to cross the junction.So the current will be small.If we increase the applied voltage significantly, the barrier height will be reduced and more number of carriers will have the required energy.Thus the current increases.


Due to the applied voltage, electrons from n-side cross the depletion region and reach p-side(Where they are minority carries).Similarly, holes from p-side cross the junction and reach the n-side(Where they are minority carries).This process under forward bias is known as minority carrier injection.At the junction boundary, on each side, the minority carrier concentration increases signifcantly compared to the locations far from the junction.
Due to this concentration gradient, the injected electrons on p-side diffuse from the junction edge of p-side to the other end of p-side.Likewise, the injected holes on n-side diffuse from the junction edge of n-side to the other end of n-side[Fig. 4].This motion of charged carriers on either side gives rise to current.The total diode forward current is sum of hole diffusion current and conventional current due to electron diffusion.The magnitude of this current is usually in mA.

Fig. 4

MAKING OF OUR CONSTITUTION

The constitution of india came into force on 26th january 1950,when india became a sovereign democratic republic.

The 42nd Amendment passed in 1976 declared india as a sovereign socialist secular democratic republic.The constitution is the framework within which a system of government operates. In simple language,it is a set of rules and laws which defines the position and powers of the three organs of the government- the legislature,the executive, and the judiciary.It defines the powers of the government at all levels- the powers of the central government and the state government as well the powers of the local agencies of the government.

It regulates the relationship between individual citizen and the state by incorparating rights and duties of citizens.India is a democratic country in which citizens have their rights and duties.

citizenship rights are given to every person who is born in india or either of whose parents was born in india or who has been a resident of india for five years,immediately preceding the commencement of the constitution.Every citizen is given some rights to ensure his all-round development.Rights imply duties.Through the 42nd Amendment of the constitution, Part 4A is added to the constitution which enumerates ten duties of the citizens.

FRAMING OF OUR CONSTITUTION:

The constitution of our country was framed by the constituent assembly which was consituted in 1946 under the provisions of the cabinet mission plan during the last phase of the british rule in india.This assembly has 389 members.Most of the members were elected by the provincial assemblies and some were nominated by the then rulers of the erstwhile native states of india.

The first meeting of the constituent assembly took place on 9th december 1946.It was presided over by Sachadanand Sinha, the oldest sitting member of the erstwhile central assembly.On 11th december 1946, the assembly elected Dr.Rajendra Prasad as its permanent chairman who was also known as the president of the consitutent assembly.

COMPOSITION OF THE CONSTITUENT ASSEMBLY:

As a result of the partition of the country into india 7 pakistan, the members of the constituent assembly of india were reduced from 389 to 308 in 1947. The constituent assembly was comprised of such eminent persons as Dr.Rajendra Prasad, Pandit jawaharlal nehru,Dr B.R.Ambedkar,Maulana Azad,K.M.Munshi,H.N.Kunzru,Sir Tej Bahadur Sapru and C.Rajagopala Chari.The assembly represented all communities and classes of the indian people.It was like the mirror of the nation reflecting the aspirations of one and all.The indian christians were represented by Dr.H.C.Mookerjee, the parsees by Dr.H.P.Modi and the Anglo-indians by Mr Frank Anthony.

It is to be noted that the cabinet mission plan had, in its original plan,guranteed seats in the constituent assembly only for minorities like the muslims and the sikhs.

DRAFTING COMMITTEE:

The constituent Assembly set uo many committes to consider matters concerning the drafting of a constitution for india.The most important of all such committees was the drafting committee which was consituted on 29th August,1947.It had seven members.Dr.B.R.Ambedkar was its chairman.The drafting committee prepared the draft constitution which was introduced in the assembly.After making several amendments to the draft constitution, the constitution of india was adopted by the constituent Assembly on 26th November,1949.
The constituent Assembly took two years,eleven months and eighteen days to complete its task of making a constitution for india.
The Constitution as a whole came into force on 26th january,1950, the day on which india became a republic.

SIGNIFICANCE OF 26TH JANUARY:

26th january was specially chosen for the promulgation of our constitution because of its apecial significance in our struggle for freedom.At the lahore session of 1929,the congress passed the poorna swaraj resolution.
The congress working committee subsequently met on 2nd january,1930 and decided to observe 26th january,1930 in calcutta(now kolkata) as the poorna swaraj day.

A COMPREHENSIVE DOCUMENT:

Our constitution is a comprehensive legal document.It contains provisions to govern the centre and the state governments.It has special clauses to safeguard the interest of the minorities,scheduled castes and scheduled tribes.It caters to the needs of people with diverse religion,caste,language,race and culture.The constitution also contains rules for elections,lists of approved languages, and other details about the conduct of the government.Our constitution in its original form had 395 articles and 8 schedules.Now it consists of the following:
1.The Preamble
2.An Appendix which contains the order extending the application of the constitution to jammu and Kashmir.