Every Book Back multiple-choice question from Electronics and Communication (12th Standard Physics, Samacheer Kalvi) — each with the correct option highlighted and a clear, worked explanation. Free to read in English and Tamil.
Q1
The barrier potential of a silicon diode is approximately,
- A. 0.7 VCorrect
- B. 0.3V
- C. 2.0 V
- D. 2.2V
Explanation. Silicon diodes require a specific forward bias voltage of approximately zero point seven volts to overcome the internal electric field at the junction and allow current to flow.
Q2
If a small amount of antimony (Sb) is added to germanium crystal,
- A. it becomes a p-type semiconductor
- B. the antimony becomes an acceptor atom
- C. there will be more free electrons than hole in the semiconductorCorrect
- D. its resistance is increased
Explanation. Antimony is a pentavalent impurity. Adding it to a tetravalent germanium crystal provides extra free electrons, making it an n-type semiconductor where electrons are the majority charge carriers.
Q3
In an unbiased p-n junction, the majority charge carriers (that is, holes) in the p-region diffuse into n-region because of
- A. the potential difference across the p-n junction
- B. the higher hole concentration in p-region than that in n-regionCorrect
- C. the attraction of free electrons of n-region
- D. All of the above
Explanation. Diffusion in semiconductors occurs when there is a concentration gradient. Holes move from the p-region, where they are numerous, to the n-region, where their concentration is much lower.
Q4
If a positive half-wave rectified voltage is fed to a load resistor, for which part of a cycle there will be current flow through the load?
- A. \(0^{\circ}–90^{\circ}\)
- B. \(90^{\circ}–180^{\circ}\)
- C. \(0^{\circ}–180^{\circ}\)Correct
- D. \(0^{\circ}–360^{\circ}\)
Explanation. A half-wave rectifier uses a diode that conducts only when forward biased. This occurs during the entire positive half-cycle of the input AC signal, corresponding to zero to one hundred eighty degrees.
Q5
The zener diode is primarily used as
- A. Rectifier
- B. Amplifier
- C. Oscillator
- D. Voltage regulatorCorrect
Explanation. Zener diodes are specifically designed to operate in the reverse breakdown region. In this mode, they maintain a nearly constant voltage across their terminals despite changes in current, making them ideal for regulation.
Q6
The principle based on which a solar cell operates is
- A. Diffusion
- B. Recombination
- C. Photovoltaic actionCorrect
- D. Carrier flow
Explanation. Solar cells utilize the photovoltaic effect, where incident light energy is absorbed by a semiconductor junction to create electron-hole pairs, generating an electromotive force.
Q7
The light emitted in an LED is due to
- A. Recombination of charge carriersCorrect
- B. Reflection of light due to lens action
- C. Amplification of light falling at the junction
- D. Large current capacity.
Explanation. When an LED is forward biased, electrons and holes move toward the junction and recombine. This process releases energy in the form of photons, producing light.
Q8
The barrier potential of a p-n junction depends on i) type of semiconductor material ii) amount of doping iii) temperature. Which one of the following is correct?
- A. (i) and (ii) only
- B. (ii) only
- C. (ii) and (iii) only
- D. (i) (ii) and (iii)Correct
Explanation. Barrier potential is a function of the intrinsic energy gap of the material, the density of impurities introduced during doping, and the thermal energy available to charge carriers.
Q9
To obtain sustained oscillation in an oscillator,
- A. Feedback should be positive
- B. Feedback factor must be unity
- C. Phase shift must be 0 or \(2\pi\)
- D. All the aboveCorrect
Explanation. Barkhausen conditions state that for sustained oscillations, the feedback must be positive, the loop gain must equal one, and the total phase shift around the loop must be zero or a multiple of two pi.
Q10
If the input to the NOT gate is A = 1011, its output is
- A. 0100Correct
- B. 1000
- C. 1100
- D. 0011
Explanation. A NOT gate is an inverter. It changes a logic state of one to zero and vice versa. Thus, for an input of one-zero-one-one, the inverted output is zero-one-zero-zero.
Q11
The given electrical network is equivalent to
- A. AND gate
- B. OR gate
- C. NOR gateCorrect
- D. NOT gate
Explanation. The overall logic function is determined by combining the individual truth tables of the interconnected gates in the network.
Q12
The output of the following circuit is 1 when the input ABC is
- A. 101Correct
- B. 100
- C. 110
- D. 010
Explanation. The inputs must be set to values that satisfy the sequential logic operations of the connected gates to result in a final output of one.
Q13
The variation of frequency of carrier wave with respect to the amplitude of the modulating signal is called
- A. Amplitude modulation
- B. Frequency modulationCorrect
- C. Phase modulation
- D. Pulse width modulation
Explanation. In frequency modulation, the carrier's frequency is modified in proportion to the instantaneous amplitude of the baseband information signal while the carrier's amplitude remains constant.
Q14
The frequency range of 3 MHz to 30 MHz is used for
- A. Ground wave propagation
- B. Space wave propagation
- C. Sky wave propagationCorrect
- D. Satellite communication
Explanation. This specific high-frequency band is used for sky wave propagation, where signals are reflected back to Earth by the ionosphere, enabling long-distance communication beyond the horizon.
About these Electronics and Communication questions
These are the Book Back multiple-choice questions for Electronics and Communication from the Tamil Nadu State Board (Samacheer Kalvi) 12th Standard Physics syllabus. Each question shows the correct option and an original, step-by-step explanation so you understand the method, not just the answer. Use the answer key above to jump to any question, then take the practice test to check yourself under exam-like conditions.
Frequently asked questions
How many MCQs are there in Electronics and Communication?
This chapter has 14 book-back multiple-choice questions, each with the correct answer and a step-by-step explanation.
Are these 12th Standard Physics MCQs free to practise online?
Yes. Every question, answer and explanation here is free, and you can also take them as a timed practice test.
Where can I find the Electronics and Communication book-back answers?
The correct option for each question is highlighted on this page with a worked explanation, plus a quick answer-key summary at the top.
