Qeqstion 4:

4.1) Step 1 :

The following are the points that can be effected by negative feedback to improve the performance of a circuit :

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• Connecting the output of an op-amp to its inverting input is called " negative feedback ".
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• This term can be broadly applied to any dynamic system where the output signal is “ fed back ” to the input somehow so as to reach a point of equilibrium (balance).
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• When the output of an op-amp is directly connected to its inverting input, a voltage follower will be created. Whatever signal voltage is impressed upon the noninverting input will be seen on the output.
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• An op-amp with negative feedback will try to drive its output voltage to whatever level necessary so that the differential voltage between the two inputs is practically zero. The higher the op-amp differential gain, the closer that differential voltage will be to zero.
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• Some op-amps cannot produce an output voltage equal to their supply voltage when saturated. The model 741 is one of these. The upper and lower limits of an op-amps output voltage swing are known as positive saturation voltage and negative saturation voltage, respectively.
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4.2).

Step 2 :

 The circuit diagram of a push-pull amplifier with two NPN transistors :

4.3).

Step 3 :

Applications of uni-junction transistor :

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• Unijunction transistor circuits allowed simple oscilators to be built using just one active device. For example, they were used for relaxation oscilators in variable-rate strobe lights.
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• Later, as integrated circuits became more popular, oscillators such as the 555 timer IC became more commonly used.
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• In addition to its use as the active device in relaxation oscilators, one of the most important applications of UJTs or PUTs is to trigger thyristors (SCR, TRIAC, etc) .
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• A DC voltage can be used to control a UJT or PUT circuit such that the "on-period" increases with an increase in the DC control voltage. This application is important for large AC current control.
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• UJTs can also be used to measure magnetic flux. The hall effect modulates the voltage at the PN junction.This affects the frequency of UJT relaxation oscillators.This only works with UJTs. PUTs do not exhibit this phenomenon.
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4.4).

Voltage gain also called voltage amplification.

Voltage gain is the ratio of amplifier output voltage to input voltage usually expressed in decibels.

Thus, .

Output voltage of the amplifier, .

Input voltage of the amplifier, .

Substitute and in .

.

From the given data, .

Thus, it is FALSE.

4.5) 

A transistor can be operated in three different regions as

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• active region
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• saturation region
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• cut-off region
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Active region:

The transistor is said to be operated in active region when the emitter-base junction is forward biased and collector –base junction is reverse biased.

Saturation region:

Transistor is said to be operated in saturation region when both EB junction and CB junction are forward biased.

Cut-off region: When both EB junction and CB junction are reverse biased, the transistor is said to be operated in cut-off region. In this region, the current in the transistor is very small and thus when a transistor in this region it is assumed to be in off state.

 4.6).

The Field Effect Transistor controls the flow of electrons or electron holes from the source to drain by affecting the size and shape of a "conductive channel" created and influenced by voltage (or lack of voltage) applied across the gate and source terminals.

Field Effect Transistor is a “ VOLTAGE ” operated device.

Therefore, the correct answer is Voltage. 

Question 5 : 5.1).

5.1.1)

The output wave forms of the integrator operational amplifier :

5.1.3)

The output wave forms of the differentiator operational amplifier :

5.1.2)

The output wave forms of the non-inverting operational amplifier :

 5.2).

High input impedance at the input terminals and low output impedance at the output terminal(s) are particularly useful features of an operational amplifier.

In the non-inverting amplifier on the right, the presence of negative feedback via the voltage divider , determines the closed-loop gain .

 In a non-inverting amplifier, the output voltage changes in the same direction as the input voltage.

Therefore, a non-inverting operational amplifier is used with out feedback.