2. Explain what is the Tri State of a Signal?

In digital ciruit, the gate output can be only high or low. In highstate the output source current at a minimum voltage, greater than ~2.8V if load(fan out ) is proper. In low state it will sink current at max output voltage less than ~0.8V. Some times it is derirable to have a state output both not high or low. with neither sinking or sourcing (with high output impedance). This is called tristate. Tristate output cannot change output condition of succeding logic gates, unless tristate is disabled.

4. Why the input resistance of an ideal OP-AMP is infinite and output resistance is zero?
secondly, how can we measure these resistances(input and output) in case of an ideal OP-AMP and Real OP-AMP in the following conditions when

Ideal OP-AMP is a power ful concept.

If one goes through the history of amplifying devices, it becomes clear that less it loads the previous stage, better the output signal. ie. it is a trend toward higher and higher input impedances.

Also it is better to maintain the signal level irrespective of the LOAD connected at the ouput. Lesser the output impedance, less the signal amplitude reduction when load is connected. ie. it is a trend toward lower and lower output impedances.

As ideal opamp is a concept , by virtue it has zero output impedance and infinite input impedance, and they are not physically measurable but has to be taken for granted for the use in theoritical analysis.

To measure input resistance, of non ideal opamp, connect a known source at the input and give a signal (within Specifications) through a current meter of sufficient precision. Input voltage by current gives the input impedance.

To measure input resistance, of non ideal opamp, connect a known source at the input and give a signal (within Specifications) through a current meter of sufficient precision. Input voltage by current gives the input impedance.

To measure output resistance, of non ideal opamp, connect a known source at the input such that the output does not saturate and connect a load (within Specifications ) through a current meter of sufficient precision and meaure the output voltage. Output voltage by current gives the output impedance.

Please refer application notes by device manufacturers freely availble in internet for more precise and practical solutions.

5. What are the differences between voltage and current controlled devices?

In any (electronic) device controlling parameter is current it is called current controlled device. eg bilpolar transistor- output current is a function of base current.

In any (electronic) device controlling parameter is voltage it is called voltage controlled device. eg Field effect transistor- output current is a function of gate voltage.

It depends on the inherent physical mechanism which defines the primary (independent) controlling parameter.

6. What is the difference between Silicon Controlled Switch (SCS) and Gate Turn-off Switch (GTO)?

SCS is nothing but the switch (sillicon controlled switch SCR),but GTO is one of the turn off method in SCR.if any other answer for this question please forward me too the answer.

8. Explain how many type of resistor are there in diode?

They are two types one is forward resistance

1.Forward resistance
2.Reverse
resistance

1.Forward resistance
This is the resistance offered in forward bias condition of the diode.
It is calculated by with the help of graph for voltage and current characteristic.

2.Reverse resistance
This resistance is offered in the reverse bias condition of the diode. It is also calculated by the same method.

9. What is Edison Effect?

In a conducting material, the electrons are governed by Fermi-Dirac statistics. The baseline electron energy is the Fermi Energy*, and at low temperatures the electrons all exist at or below this level. As temperature is increased, so the distribution function for the electrons develops a high energy 'tail'. Some of these electrons have sufficient energy to pass over the surface potential barrier between the material and the vacuum. This process of increasing the temperature of a bulk material to increase the number of electrons which can leave the material is called thermionic emission or Edison effect.