Learn important MCQs (with solutions) for CBSE Class 12th Physics Board Exam 2020 (Chapter 14- Semiconductor Electronics: Material, Devices & Simple Circuits). Here you will also get important links to access some important articles for the preparation of CBSE 12th board exams 2020. Students preparing for CBSE Class 12th Physics Board Exam 2020 usually ask about important MCQs (Multiple Choice Questions) & here we have provided important questions (with solution), based on Chapter 14 (Semiconductor Electronics: Material, Devices & Simple Circuits) of Class 12th Physics NCERT textbook.
Important MCQs for CBSE Class 12 Physics Board Exam 2020 (Chapter 14 - Semiconductor Electronics: Material, Devices and Simple Circuits):
Q1. In a half wave rectifier circuit operating from 50 Hz mains frequency, the fundamental frequency in the ripple would be
(a) 25 Hz
(b) 50 Hz
(c) 70.7 Hz
(d) 100 Hz
As, the output voltage obtained in a half wave rectifier circuit has single variation in one cycle of AC voltage, therefore the fundamental frequency in the ripple of output voltage would be 50 Hz.
Q2. The probability of finding electrons in the conduction band of an intrinsic semiconductor at a finite temperature
(a) increases exponentially with increasing band gap
(b) decreases exponentially with increasing band gap
(c) decreases with increasing temperature
(d) is independent off the temperature and band gap
If band gap is increased, the probability of finding electrons in the conduction band decreases exponentially. It is so because it will be more difficult for the electron to cross over the band gap while going from valence band to conduction band.
Q3. In p-n junction, the barrier potential offers resistance to
(a) only free electrons in n- region
(b) only holes in p-region
(c) free electrons in n-region and holes in p-region
(d) free electrons in p-region and holes in n-region
In p-n junction free electrons of n-region and holes of p-region are stopped to migrate due to potential barrier across barrier junction.
Q4. Symbolic representation of four logic gates are shown below
Pick out which ones are for AND, NAND and NOT gates, respectively
(a) (ii), (iii) and (iv)
(b) (iii), (ii) and (i)
(c) (iii), (ii) and (iv)
(d) (ii), (iv) and (iii)
Here, (i) represents OR gate, (ii) represents AND gate, (iii) represents NOT gate and (iv) represents NAND gate.
Q6. Carbon, silicon and germanium have four valence electrons each. These are characterized by valence and conduction bands separated by energy band gap respectively equal to (Eg)c,(Eg)Si and (Eg)Ge, Which of the following statements is true?
(a) (Eg)Si < (Eg)Ge < (Eg)c
(b) (Eg)c< (Eg)Ge< (Eg)Si
(c) (Eg)c> (Eg)Si> (Eg)Ge
(d) (Eg)c = (Eg)Si = (Eg)Ge
The energy band gap is greatest for carbon, less for silicon and least for germanium out of the given three elements. Hence answer (c) is correct.
Q7. A p-n junction is fabricated from a semiconductor with band gap of 3.0 eV. The wavelength of the radiation which it can detect is
(a) 600 nm
(b) 400 nm
(c) Both of these
(d) None of these
Similarly if we calculate the energy for the light having wavelength λ = 400 nm then, the energy, E = 3.1 eV > 3.0 eV. In this case E>Eg, then p-n junction can detect the radiation of wavelength 400 nm.
Q9. The forbidden energy band gap in conductors, semiconductors and insulators are EG1, EG2 and EG3 respectively. The correct relation is:
(a) EG3 > EG2> EG1
(b) EG3 < EG2> EG1
(c) EG3 > EG2> EG1
(d) EG3 < EG2< EG1
The correct relation is: EG3 > EG2> EG1.
Q10. In a common base circuit, the current gain is 0.96. If the base current is 60μ A, the emitter current and collector current
(a) 2 mA
(b) 4 mA
(c) 2.2 mA
(d) 1.4 mA