Q.No.1:
What is the Intrinsic semiconductor? Name two such materials.
Ans:
An Intrinsic semiconductoris a pure semiconductor without any significant dopant species present. The number of charge carriers is therefore determined by the properties of the material itself instead of the amount of impurities.
In intrinsic semiconductors the number of excited electrons and the number of holes are equal:
n = p.
Because they are thermally generated.If an electron breaks its covalent bond we have one free electron and one hole.
The Pure Silicon, Pure germanium and pure gallium arsenide are Intrinsic material.
Q.No.2:
Define behavior of Minority and majority carriers in an PN junction under reverse bias.
Ans:
When reverse voltage is applied, free electrons (majority carriers) and holes (minority carriers) move away from the junction leaving behind positive (+ive) and negative (-ive) ions. Holes move towards cathode and electrons move towards anode.
As a result Depletion region gets wider. The greater the reverse voltage, the greater the depletion region becomes, and greater the potential barrier becomes. Potential Hill increases which opposes free electrons from entering across the Junction.
Q.No.3:
Explain the formation of depletion region in an un-biased condition.
Ans:
For formation of depletion region, we take two semiconductor materials, one n-type and the other p-type. An n-type semiconductor has electrons as the majority carriers, and a p-type semiconductor has holes as the majority carriers.
We know that holes are majority carriers in p-type, and electrons are majority carriers in n-type materials. The electrons and holes diffuses in to opposite type. “These two layers of positive and negative ions form the depletion region. The term “depletion” refers to the fact that the region near the junction is depleted of their respective majority chargecarriers.”
The diffusion does not occur indefinitely and it stops after a quick span of time and the depletion region is said to be completely formed.
In unbiased semiconductors,if no voltage applied is across a semiconductor diode(un-biased), than a thin depletion region is developed around the region of the P-N junction. The depletion region is almost free of charge carriers, and acts as an insulator, preventing the current flow.
Q.No.4:
Define Peak, Average and RMS value of Sine wave.
Ans:
Peak:
The Peak value of the wave is the highest value the wave reaches above a reference value. The reference value normally used is zero. In a voltage waveform the peak value may be labelled VPK or VMAX.
If the sine wave being measured is symmetrical either side of zero volts (or zero amperes), meaning that the dc level or dc component of the wave is zero volts, then the peak value must be the same as the amplitude, that is half of the peak to peak value.
Average Value:
This is normally taken to mean the average value of only half a cycle of the wave. If the average of the full cycle was taken it would of course be zero, as in a sine wave symmetrical about zero, there are equal excursions above and below the zero line.
RMS Value:
The RMS or Root Mean Squared value is the value of the equivalent direct (non varying) voltage or current which would provide the same energy to a circuit as the sine wave measured.
VRMS = VPK x 0.707 and IRMS = IPK x 0.707
Q.No.5:
Logically show how three different signals can be transmitted on a single transmission line.
Ans:
While transmitting three different signals from one transmission line, we have some different possibilities. One is that, we can transmit all the signals with isolation, one by one. Second is that, we can also transfer the signals one by one on a same transmission line using some appropriate timings but only one station can transmit at a time. The entire frequency line spectrum of a transmission line is used. When a signal is inserted at any point on a transmission medium, it propagates in all directions until it reaches at the destination (end).
Q.No.6:
Explain the specific resistance. If specific resistance of a material is 2Ohm. Consider a slabof same material having dimensions: 2m x 3m x 4m.
Ans:
The specific electrical resistance of a conductor depends on its material and temperature. The mount of resistance in the flow of current, cross sectional area is called “specific resistance” of that conductor.
It is the property of resistance.Resistivity is the reciprocal of conductivity. A substance that has a high resistivity will have a low conductivity, and vice versa.The resistance of a conductor of a uniform cross section varies directly as the product of the length and the specific resistance of the conductor, and inversely as the cross-sectional area of the conductor.
Q.No.7:
Find Vout.
Ans:
Calculations:
Q.No.8:
How di-electric material effects the capacitance of the capacitor.
Ans:
If a material contains polar molecules, they will generally be in random orientations when no electric field is applied. An applied electric field will polarize the material by orienting the dipole moments of polar molecules.
This decreases the effective electric field between the plates and will increase the capacitance of the parallel plate structure. The dielectric must be a good electric insulator so as to minimize any DC leakage current through a capacitor.
Also, greater permittivity of the dielectric gives greater capacitance; less permittivity of the dielectric gives less capacitance.
Q.No.9:
Explain Charge, Voltage and Current. Give analogies to make a clear picture of these quantities.
Ans:
Charge:
Electric charge is the physical property of matter that causes it to experience a force when placed in an electromagnetic field. There are two types of electric charges: positive and negative. Positively charged substances are repelled from other positively charged substances, but attracted to negatively charged substances; negatively charged substances are repelled from negative and attracted to positive.
Voltage:
Voltage is the electric energy charge difference of electric potential energy transported between two points. Voltage is equal to the work done per unit of charge against a static electric field to move the charge between two points.
A voltage may represent either a source of energy (electromotive force), or lost, used, or stored energy (potential drop). A voltmeter can be used to measure the voltage (or potential difference) between two points in a system.
Current:
Current is the rate of flow of electrical charge carriers, usually electrons or electron-deficient atoms. The common symbol for current is the uppercase letter I. The standard unit is the ampere, symbolized by A.
Electric current can be either direct or alternating. Direct current (DC) flows in the same direction at all points in time. In an alternating current (AC), the flow of charge carriers reverses direction periodically.
Consider the example of flowing water and circuit. Charge is like water that is flow at some rate called current and water is fall through some height which in circuit theory called voltage that provide place to current to flow.
Q.No.10:
Explain in detail.
I. C = e x A/d
II. C = Q / V
For a capacitance shown.
Ans:
The amount of charge that can be placed on a capacitor is proportional to the voltage pushing the charge onto the positive plate. The larger the potential difference (voltage) between the plates, the larger the charge on the plates:
Q = C V
The constant of proportionality is called the "capacitance" and is proportional to the area (A) of one of the plates and inversely proportional to the separation between the plates (d):
C = e A / d
For a parallel plate capacitor,
where e is the permittivity of the insulating material (or DIELECTRIC) between the plates.
That’s why the capacitance increases if the area A of the plates is increased or their separation decreased.
If we consider the formula for the parallel-plate capacitor we can see what happens as we change the plate separation. There are two different cases to consider:
(a) Where the capacitor remains connected to the source of electrical potential, and
(b) Where the capacitor is disconnected after the initial charge Q has been placed on the plates.
