## ELECTRONICS-QUIZ 12

As per analysis for previous years, it has been observed that students preparing for NEET find Physics out of all the sections to be complex to handle and the majority of them are not able to comprehend the reason behind it. This problem arises especially because these aspirants appearing for the examination are more inclined to have a keen interest in Biology due to their medical background. Furthermore, sections such as Physics are dominantly based on theories, laws, numerical in comparison to a section of Biology which is more of fact-based, life sciences, and includes substantial explanations. By using the table given below, you easily and directly access to the topics and respective links of MCQs. Moreover, to make learning smooth and efficient, all the questions come with their supportive solutions to make utilization of time even more productive. Students will be covered for all their studies as the topics are available from basics to even the most advanced. .

Q1. The plate current in a vacuum diode depends on
•  Cathode temperature only
•  Plate voltage only
•  Both plate voltage and cathode temperature
•  None of these
Solution
(c)Both plate voltage and cathode temperature

Q2.The depletion layer of a p-n junction
•  Is of constant width irrespective of the bias
•  Acts like an insulating zone under reverse bias
•  Has a width that increases with an increase in forward bias
•  Is depleted of ions
Solution
(b)Acts like an insulating zone under reverse bias

Q3. In a transistor the collector current is always less than the emitter current because
•  Collector side is reverse biased and the emitter side is forward biased
•  A few electrons are lost in the base and only remaining ones reach the collector
•  Collector being reverse biased, attracts less electrons
•  Collector side is forward biased and emitter side is reverse biased
Solution
(b) Due to forward bias at the emitter-base junction, the majority charge carrier electrons of emitter get repelled from the negative terminal and move towards base. Some of these electrons combine with the majority charge carrier holes present in the base and most of the electrons reach the collector, crossing the collector-base junction. This implies that collector current is always less than the emitter current due to the reason (b).

Q4. Figure shows a diode connected to an external resistance and an emf. Assuming that the barrier potential developed in diode is 0.5 V, obtain the value of current in the circuit in milli ampere.

•  40 mA
•  60 mA
•  80 mA
•  100 mA
Solution
(c)80 mA

Q5.Which of the following is a dichroic crystal
•  Mica
•  Selenite
•  Quartz
•  Tourmaline
Solution
(d) Tourmaline is the dichroic crystal

Q6. Zener breakdown in a semi-conductor diode occurs when
•  Forward current exceeds certain value
•  Reverse bias exceeds certain value
• Forward bias exceeds certain value
•  Potential barrier is reduced to zero
Solution
(b) When reverse bias is increased, the electric field at the junction also increases. At some stage the electric field breaks the covalent bond, thus the large number of charge carriers are generated. This is called Zener breakdown

Q7.The band gap in germanium and silicon in eV respectively is
•  0.7, 1.1
•  1.1, 0.7
•  1.1, 0
•  0, 1.1
Solution
(a)0.7, 1.1

Q8.The difference in the variation of resistance with temperature in a metal and a semiconductor arises essentially due to the difference in the
•  Crystal structure
•  Variation of the number of charge carries with temperature
•  Type of bonding
•  Variation of scattering mechanism with temperature
Solution
(b) The difference in the variation of resistance with temperature in metal and semiconductor is caused due to difference in the variation of the number of charge carriers with temperature.

Q9.A photodetector used to detect the wavelength of 1700 nm, has energy gap of about
•  0.073 eV
•  1.2 eV
•  7.3 eV
•  0.73 eV
Solution
(d)Energy = hc/Î»=(6.6×10-34×3×108)/(1700×10-9×1.6×10-19 ) eV = 0.73 eV

Q10. A piece of copper and another of germanium are cooled from room temperature to 77 K, the resistance of
•  Each of them increases
•  Each of them decreases
•  Copper decreases and germanium increases
•  Copper increases and germanium decreases
Solution
(c) We know that resistance of conductor is directly proportional to temperature (ie, R∝∆t), while resistance of semiconductor is inversely proportional to temperature (ie,R∝1/∆t). Therefore, it is clear that resistance of conductor decreases with decrease in temperature of vice-versa, while in case of semiconductor, resistance increase with decrease in temperature of vice-versa. Since, copper is pure conductor and germanium is a semiconductor hence, due to decrease in temperature, resistance of conductor decreases while that of semiconductor increases

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