12th Class Physics Sample Paper Physics Sample Paper-4

  • question_answer
    (i) Write the function of
    (a) Transducer and
    (b) Repeater in the context of communication system.
    (ii) Write two factors justifying the need of modulation for transmission of a signal.


    (a) Transducer Transducer is a device that converts one form of energy into another. For example, an electrical transducer can convert any physical quantity like pressure or displacement into corresponding electrical signal, e.g. Microphone.
    (b) Repeater It is a combination of a transmitter and a receiver. A repeater is used to extend the range of a communication system. e.g. Communication satellite.
    (ii) Need for modulation Usually the transmitting signals are of low frequency.
    It is modulated using a carrier wave of very high frequency.
    The resultant modulated signal has very high frequency. This is done for the following reasons:
    (a) The antenna length should have a size comparable to the wavelength of signal. If the frequency is high, wavelength will be less. So, the antenna length is also reasonable.
    (b) The power radiated is proportional to \[1/{{\lambda }^{2}}.\] So by decreasing \[\lambda ,\] power radiated can be increased for the same antenna length.
    (c) Suppose there are many transmitting signals to be transmitted, then there are chances that the signals get mixed up. To avoid this, a band of frequencies are alloted to each message signal and then transmitted. This is possible only in high frequency communication.

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