Learn important MCQs (with solutions) for CBSE Class 12th Physics Board Exam 2020 (Chapter 15 - Communication Systems). 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 15 (Communication Systems) of Class 12th Physics NCERT textbook.
Important MCQs for CBSE Class 12 Physics Board Exam 2020(Chapter 15 - Communication Systems):
Q1. The radio waves of frequency 300 MHz to 3000 MHz belong to
(a) High frequency band
(b) Ultra high frequency band
(c) Very high frequency band
(d) Super high frequency band
Radio waves of frequency 300 MHz to 3000 MHz belongs to ultra high frequency band.
Q2. Which of the following mode of propagation is used to send radio-waves from one place to another?
(a) Space wave propagation
(b) Sky wave propagation
(c) Ground wave propagation
(d) All of them
The radio waves can be sent from one place to another through ground wave propagation, sky wave propagation and space wave propagation.
Q3. A TV tower has a height of 100 m. The maximum distance upto which the T.V. Trans- mission can be received (Radius of earth = 8 X 106 m)?
(a) 34.77 km
(b) 32.70 km
(c) 40 km
(d) 40.70 km
Q4. Which of the following is not transducer?
(d) All of these
Transducer is a device used for converting a one form of energy into another. Therefore, the term transducer is applied to gramophone pickups, microphones and loudspeakers but not for amplifier.
Q5. A carrier wave is modulated by n number of sine waves with modulation indices μ1, μ2, μ3…. The total modulation index (μ) of the wave is
Q6. Modulation is the process of superposing
(a) high frequency audio signal on low frequency audio signal
(b) high frequency message signal on low frequency audio waves
(c) low frequency message signal on high frequency waves
(d) low frequency radio signal on high frequency audio waves
Modulation is the process of superposing the low frequency audio signal on high frequency wave.
Q7. The circuit diagram of an AM demodulator is given below. The correct relation between carrier frequency (f) and RC for best quality demodulation is:
(a) RC = 1/
(b) RC < 1/
(c) RC ≤ 1/
(d) RC >> 1/
For best quality demodulation,1/f << RC or RC >> 1/f.
Q8. If both the length of an antenna and the wave length of the signal to be transmitted are doubled, the power radiated by the antenna
(a) is doubled
(b) is halved
(c) increases 16 times
(d) remains constant
Power radiated by the antenna is proportional to (l/λ)2.
When both, the length of the antenna l and wavelength of the signal λ are doubled then remains unchanged. So, the power radiated by antenna will remain unchanged.
Q9. Which mode of communication is/are not employed for the transmission of T.V. signals?
(a) Ground wave propagation
(b) Sky wave propagation
(c) Both (a) and (b)
(d) None of these
The mode of communication used for T.V. signals transmission is either space wave propagation, i.e., line of sight propagation or satellite communication.
Q10. A transmitting antenna at the top of a tower has a height 3200 cm and that of the receiving antenna is 5000 cm. The maximum distance between them for satisfactory communication in line of sight mode is:
(Radius of earth = 6.4 X 106 m)
(a) 1.5 × 103 m
(b) 5.5 × 103 m
(c) 4.5 × 103 m
(d) 4.5 × 104 m