Semiconductors & Communication · JEE Main previous year questions

2017 4 questions

1. Q592017 · 9 Apr 2017 · Shift 1

   The current gain of a common emitter amplifier is 69. If the emitter current is 7.0 mA, collector current is :

   1. A.9.6 mA
   2. B.6.9 mA
   3. C.0.69 mA
   4. D.69 mA
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   Answer: B

2. Q602017 · 9 Apr 2017 · Shift 1

   A signal is to be transmitted through a wave of wavelength $\lambda$, using a linear antenna. The length l of the antenna and effective power radiated ${\mathrm{P}}_{\mathrm{eff}}$ will be given respectively as : (K is a constant of proportionality)

   1. A.$\lambda$, ${\mathrm{P}}_{\mathrm{eff}}=\mathrm{K}{\left(\frac{l}{\lambda }\right)}^2$
   2. B.$\frac{\lambda }{8}$, ${\mathrm{P}}_{\mathrm{eff}}=\mathrm{K}\left(\frac{l}{\lambda }\right)$
   3. C.$\frac{\lambda }{16}$, ${\mathrm{P}}_{\mathrm{eff}}=\mathrm{K}{\left(\frac{l}{\lambda }\right)}^3$
   4. D.$\frac{\lambda }{5}$, ${\mathrm{P}}_{\mathrm{eff}}=\mathrm{K}\left(\frac{l}{\lambda }\right){\left(\frac{l}{\lambda }\right)}^{\frac{1}{2}}$
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   Answer: A

3. Q472017 · 8 Apr 2017 · Shift 1

   What is the conductivity of a semiconductor sample having electron concentration of $5\times 10^{18}{m}^{-3}$, hole concentration of $5\times 10^{19}{m}^{-3}$, electron mobility of $2.0{\mathrm{m}}^2{\mathrm{V}}^{-1}{\mathrm{s}}^{-1}$ and hole mobility of $0.01{\mathrm{m}}^2{\mathrm{V}}^{-1}{\mathrm{s}}^{-1}$ ? (Take charge of electron as $1.6\times 10^{-19}\mathrm{C}$)

   1. A.$1.68(\Omega \text{-}\mathrm{m}{)}^{-1}$
   2. B.$1.83(\Omega \text{-}\mathrm{m}{)}^{-1}$
   3. C.$0.59(\Omega \text{-}\mathrm{m}{)}^{-1}$
   4. D.$1.20(\Omega \text{-}\mathrm{m}{)}^{-1}$
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   Answer: A

4. Q602017 · 8 Apr 2017 · Shift 1

   A signal of frequency 20 kHz and peak voltage of 5 Volt is used to modulate a carrier wave of frequency 1.2 MHz and peak voltage 25 Volts. Choose the correct statement.

   1. A.Modulation index = 5, side frequency bands are at 1400 kHz and 1000 kHz
   2. B.Modulation index = 5, side frequency bands are at 21.2 kHz and 18.8 kHz
   3. C.Modulation index = 0.8, side frequency bands are at 1180 kHz and 1220 kHz
   4. D.Modulation index = 0.2, side frequency bands are at 1220 kHz and 1180 kHz
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   Answer: D