# Multiple choice question for engineering

## Set 1

1. A transistor with ß = 120 is biased to operate at a dc collector current of 1.2 mA. Find the value of gm.

a) 12mA/V

b) 24 mA/V

c) 36 mA/V

d) 48 mA/V

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2. A transistor with ß = 120 is biased to operate at a dc collector current of 1.2 mA. Find the value of R?p.

a) 625 ohm

b) 1250 ohm

c) 2500 ohm

d) 5000 ohm

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3. A transistor with ß = 120 is biased to operate at a dc collector current of 1.2 mA. Find the value of Re.

a) 2.5 ohm

b) 20.6 ohm

c) 25.2 ohm

d) 30.4 ohm

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4. A transistor operating with nominal gm of 60 mA/V has a ß that ranges from 50 to 200. Also, the bias circuit, being less than ideal, allows a 20% variation in Ic. What is the smallest value found of the resistance looking into the base?

a) 347 ohm

b) 694 ohm

c) 1041 ohm

d) 1388 ohm

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5. A transistor operating with nominal gm of 60 mA/V has a ß that ranges from 50 to 200. Also, the bias circuit, being less than ideal, allows a 20% variation in Ic. What is the largest value found of the resistance looking into the base?

a) 1050 ohm

b) 21000 ohm

c) 3150 ohm

d) 4200 ohm

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6. A designer wishes to create a BJT amplifier with a gm of 50 mA/V and a base input resistance of 2000 O or more. What is the minimum ß he can tolerate for the transistor used?

a) 100

b) 150

c) 200

d) 250

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7. A designer wishes to create a BJT amplifier with a gm of 50 mA/V and a base input resistance of 2000 O or more. What emitter bis current should he choose?

a) 1.06 mA

b) 1.16 mA

c) 1.26 mA

d) 1.36 mA

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8. Which of the following is true?

a) Ib = ß Ic

b) Ib = ß + 1/ Ic

c) Ib = Ic/ß

d) Ib = Ic/ ß – 1

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9. The SI units of transconductance is

a) Ampere/ volt

b) Volt/ ampere

c) Ohm

d) Siemens

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10. Which of the following represents the correct mathematical form of the term denoted by the symbol Rp?

a) ß/gm

b) Vt/Ib

c) All of the mentioned

d) None of the mentioned

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## Set 2

(Q.1-Q.3) A pseudo-noise (PN) sequence is generated using a feedback shift register of length m = 4. The chip rate is 107 chips per second.

1. The PN sequence length is

a) 10

b) 12

c) 15

d) 18

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^{m}– 1 = 16 – 1 = 15.

2. The chip duration is

a) 1µs

b) 0.1 µs

c) 0.1 ms

d) 1 ms

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^{7}) or 0.1 µs.

3. The period of PN sequence is

a) 1.5 µs

b) 15 µs

c) 6.67 ns

d) 0.67 ns

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4. A slow FH/MFSK system has the following parameters.

Number of bits per MFSK symbol = 4

Number of MFSK symbol per hop = 5

The processing gain of the system is

a) 13.4 dB

b) 37.8 dB

c) 6 dB

d) 26 dB

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5. A fast FH/MFSK system has the following parameters.

Number of bits per MFSK symbol = 4

Number of pops per MFSK symbol = 4

The processing gain of the system is

a) 0 dB

b) 7 dB

c) 9 dB

d) 12 dB

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(Q.6-Q.7) A rate 1/2 convolution code with dfrec = 10 is used to encode a data sequence occurring at a rate of 1 kbps. The modulation is binary PSK. The DS spread spectrum sequence has a chip rate of 10 MHz.

6. The coding gain is

a) 7 dB

b) 12 dB

c) 14 dB

d) 24 dB

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7. The processing gain is

a) 14 dB

b) 37 dB

c) 58 dB

d) 104 dB

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^{7})/(2 x 1000) = 5000 or 37 db.

(Q.8-Q.9) An FH binary orthogonal FSK system employs an m 15 stage liner feedback shift register that generates an ML sequence. Each state of the shift register selects one of L non over lapping frequency bands in the hopping pattern. The bit rate is 100 bits/s. The demodulator employ non coherent detection.

8. If the hop rate is one per bit, the hopping bandwidth

for this channel is

a) 6.5534 MHz

b) 9.4369 MHz

c) 2.6943 MHz

d) None of the mentioned

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^{m}– 12

^{15}= 32767 bits For binary FSK modulation, the minimum frequency separation is 2/T, where 1/T is the symbol (bit) rate. The hop rate is 100 hops/sec. Since the shift register has L 32767 states and each state utilizes a bandwidth of 2/T = 200 Hz, then the total bandwidth for the FH signal is 6.5534 MHz.

9. Suppose the hop rate is increased to 2 hops/bit and the receiver uses square law combining the signal over two hops. The hopping bandwidth for this channel is

a) 3.2767 MHz

b) 13.1068 MHz

c) 26.2136 MHz

d) 1.6384 MHz

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10. In a fast FH spread spectrum system, the information is transmitted via FSK with non coherent detection. Suppose there are N = 3 hops/bit with hard decision decoding of the signal in each hop. The channel is AWGN with power spectral density 0.5No and an SNR 20 ~13 dB (total SNR over the three hops). The probability of error for this system is

a) 0.013

b) 0.0013

c) 0.049

d) 0.0049

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## Set 3

1. The magnitude of the electric charge (e) is given by ____________

a) -1.6*10^{-19} C

b) 1.6*10-^{19} C

c) 9.11*10-^{31} C

d) 1.637*10^{-37} C

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^{-19}C, the negative sign indicates the direction of force.

2. What is the forbidden gap voltage for silicon material?

a) 1.46 V

b) 1.56 V

c) 10 V

d) 1.21 V

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3. Which of the following parameters of P-N junction diode increases with temperature.

a) Cut in voltage

b) Reverse saturation current.

c) Ideality factor

d) Resistance

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_{2}is 2

^{[(T2 –T1)/10]}times greater than reverse saturation current at temperature T

_{1}where T

_{2}is greater than T

_{1}.

4. Which of the following diodes do not exhibits a constant reverse saturation current with the change in reverse saturation voltage.

a) 1N909

b) 1N405

c) 1N207

d) 1N676

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5. Which of these P-N junction characteristics are not dependent on temperature.

a) Junction resistance

b) Reverse saturation current

c) Bias current

d) Barrier voltage

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6. As the temperature to the P-N junction increases the current increases due to?

a) Leakage in bias region

b) Electron-hole pair

c) Leakage in P region

d) Leakage in N region

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7. By what percentage the reverse saturation current increases with 10 C rise in the temperature.

a) 25%

b) 12.5%

c) 50%

d) 7%

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8. What will be the decrease of barrier voltage with the rise in 10C in temperature?

a) 10V

b) 1mV

c) 10mV

d) 2mV

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9. What will be the reverse saturation current in the junction when the voltage across the junction is 0?

a) 0.3A

b) 0.7A

c) 0A

d) 1.24A

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10. The breakdown voltage of the P-N junction diode decreases due to the increase in.

a) Reverse saturation current

b) Reverse leakage current

c) Bias voltage

d) Barrier voltage

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## Set 4

1. If ‘X’ corresponds to a tunnel diode and ‘Y’ to an avalanche diode, then__________

a) X operates in reverse bias and Y operates in forward bias

b) X operates in reverse bias and Y operates in reverse bias

c) X operates in forward bias and Y operates in forward bias

d) X operates in forward bias and Y operates in reverse bias

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2. The range of tunnel diode voltage V_{D}, for which slope of its V-I characteristics is negative would be? (The V_{P} is the peak voltage and V_{V} is the valley voltage).

a) V_{D} > 0

b) 0_{P}

c) V_{V} > V_{D} > V_{P}

d) V_{D} > V_{V}

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_{V}and V

_{P}. Here, it offers negative resistance. The characteristics are depicted below:

3. Tunnel diode has a very fast operation in__________

a) gamma frequency region

b) ultraviolet frequency region

c) microwave frequency region

d) radio frequency region

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4. Which of the following are true about a tunnel diode?

1) it uses negative conductance property

2) it operates at high frequency

3) fermilevel of p side becomes higher than the n side in forward bias

a) 1 only

b) 1 and 2

c) 3 only

d) 2 and 3

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5. The depletion layer of tunnel diode is very small beacause______

a) its abrupt and has high dopants

b) uses positive conductance property

c) its used for high frequency ranges

d) tunneling effect

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6. With interments of reverse bias, the tunnel current also increases because________

a) electrons move from balance band of pside to conduction band of nside

b) fermi level of pside becomes higher than that of nside

c) junction currrent decreases

d) unequality of n and p bandedge

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7. The tunnneling involves_______

a) acceleration of electrons in p side

b) movement of electrons from n side conduction band to p side valance band

c) charge distribution managementin both the bands

d) positive slope characteristics of diode

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8. Tunnel diodes are made up of________

a) Germanium and silicon materials

b) AlGaAs

c) AlGaInP

d) ZnTe

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9. For a tunnel diode, when ‘p’ is probability that carrier crosses the barrier, ’e’ is energy,’w’ is width.

a) p ∝ e^{(-A*e*w)}

b) p ∝ 1/ e^{(-A*e*w)}

c) p ∝ e^{(A*e*w)}

d) p ∝ 1/e^{(A*e*w)}

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10. In the construction of tunnnel diode,why is the pellet soldered to anode contact and a tindot to cathode contact via a mesh screen?

a) for better conduction and reduce inductance respectively

b) for heat dissipation and increase conduction respectively

c) for heat dissipation and reduce induction respectively

d) for better conduction and reduce inductance respectively

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11. What happens to a tunnel diode when the reverse bias effect goes beyond the valley point?

a) it behaves as a normal diode

b) it attains increased negative slope effects

c) reverse saturation current increases

d) beacomes independent of temperature

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## Set 5

1. [T] = ?

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2. [h] = ?

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3. [y] = ?

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4.The [y] parameter of a two port network is given by

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5. The [y] parameter for a 2-port network and the network itself are given below.

The value of Vo/vs is _______

a) 3/32

b) 1/16

c) 2/33

d) 1/17

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6. [y] = ?

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7. A 2-port resistive network satisfy the condition A = D = 3/2B = 4/3C. The z11 of the network is

a) 4/3

b) 3/4

c) 2/3

d) 3/2

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8. A 2-port network is driven by a source Vs = 100 V in series with 5 ohm, and terminated in a 25 ohm resistor. The impedance parameters are

The Thevenin equivalent circuit presented to the 25 ohm resistor is

a) 80 V, 2.8 ohm

b) 160 V, 6.8 ohm

c) 100 V, 2.4 ohm

d) 120 V, 6.4 ohm

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9. Find V1 and V2.

a) -68.6 V, 114.3 V

b) 68.6 V, -114.3 V

c) 114.3 V, -68.6 V

d) -114.3 V, 68.6 V