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Read the following paragraph and answer the questions that follow.
| A semiconductor diode is basically a pn junction with metallic contacts provided at the ends for the application of an external voltage. It is a two-terminal device. When an external voltage is applied across a semiconductor diode such that the p-side is connected to the positive terminal of the battery and the n-side to the negative terminal, it is said to be forward-biased. When an external voltage is applied across the diode such that the n-side is positive and the p-side is negative, it is said to be reverse-biased. An ideal diode is one whose resistance in forward biasing is zero and the resistance is infinite in reverse biasing. When the diode is forward biased, it is found that beyond forward voltage called knee voltage, the conductivity is very high. When the biasing voltage is more than the knee voltage the potential barrier is overcome and the current increases rapidly with an increase in forward voltage. When the diode is reverse biased, the reverse bias voltage produces a very small current of about a few microamperes which almost remains constant with bias. This small current is a reverse saturation current. |
- In the given figure, a diode D is connected to an external resistance R = 100 Ω and an emf of 3.5 V. If the barrier potential developed across the diode is 0.5 V, the current in the circuit will be:
(a) 40 mA
(b) 20 mA
(c) 35 mA
(d) 30 mA - In which of the following figures, the pn diode is reverse biased?
(a)
(b)
(c)
(d)
- Based on the V-I characteristics of the diode, we can classify the diode as:
(a) bilateral device
(b) ohmic device
(c) non-ohmic device
(d) passive element
OR
Two identical PN junctions can be connected in series by three different methods as shown in the figure. If the potential difference in the junctions is the same, then the correct connections will be:
(a) in the circuits (1) and (2)
(b) in the circuits (2) and (3)
(c) in the circuits (1) and (3)
(d) only in the circuit (1) 
The V-I characteristic of a diode is shown in the figure. The ratio of the resistance of the diode at I = 15 mA to the resistance at V = -10 V is
(a) 100
(b) 106
(c) 10
(d) 10-6
Concept: Semiconductor Diode
A signal of 5 kHz frequency is amplitude modulated on a carrier wave of frequency 2 MHz. What are the frequencies of the side bands produced?
Concept: Amplitude Modulation (AM)
Why is base band signal not transmitted directly? Give any two reasons
Concept: Need for Modulation and Demodulation
State three important factors showing the need for translating a low frequency signal into a high frequency wave before transmission
Concept: Modulation and Its Necessity
Draw a sketch of a sinusoidal carrier wave along with a modulating signal and show how these are superimposed to obtain the resultant amplitude modulated wave
Concept: Modulation and Its Necessity
The carrier wave is given by
C(t) = 2sin(8πt) volt.
The modulating signal is a square wave as shown. Find modulation index.
Concept: Modulation and Its Necessity
Write the functions of the following in communication systems:
Modulator
Concept: Basic Terminology Used in Electronic Communication Systems
Write the functions of the following in communication systems:
Transducer
Concept: Basic Terminology Used in Electronic Communication Systems
Write the functions of the following in communication systems:
Demodulator
Concept: Basic Terminology Used in Electronic Communication Systems
Why is Modulation index kept low?
Concept: Modulation and Its Necessity
What is the role of a bandpass filter?
Concept: Modulation and Its Necessity
Distinguish between broadcast mode and point-to-point mode of communication and give one example for each.
Concept: Basic Terminology Used in Electronic Communication Systems
A device X used in communication system can convert one form of energy into another. Name the device X. Explain the function of a repeater in a communication system.
Concept: Basic Terminology Used in Electronic Communication Systems
Distinguish between point to point and broadcast modes of communication. Give an example of each.
Concept: Basic Terminology Used in Electronic Communication Systems
Answer the following question :
Define 'bandwidth' and describe briefly its importance in communicating signals ?
Concept: Bandwidth of Signals
The carrier wave is represented by
Concept: Modulation and Its Necessity
The carrier wave of a signal is given by C(t) = 3 sin (8πt) volt. The modulating signal is a square wave as shown. Find its modulation index.
Concept: Modulation and Its Necessity
Write any two factors which justify the need for modulating a signal ?
Concept: Bandwidth of Signals
Draw a diagram showing an amplitude modulated wave by superposing a modulating signal over a sinusoidal carrier wave.
Concept: Bandwidth of Signals
Write briefly any two factors which demonstrate the need for modulating a signal. Draw a suitable diagram to show amplitude modulation using a sinusoidal signal as the modulating signal.
Concept: Bandwidth of Signals
