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JEE Main & Advanced JEE Main Paper (Held On 10-Jan-2019 Evening)

  • question_answer
    The modulation frequency of an AM radio station is 250 kHz, which is 10% of the carrier wave. If another AM station approaches you for license what broadcast frequency will you allot? [JEE Main Online Paper (Held On 10-Jan-2019 Evening]

    A) 2900 kHz                                  

    B) 2750 kHz

    C) 2250 kHz          

    D)                  2000 kz

    Correct Answer: D

    Solution :

    Amplitude modulated wave consist of three Waves \[{{f}_{c}},\text{ }{{f}_{c}}-\text{ }{{f}_{m}}-{{f}_{c}}+{{f}_{m}}\] \[{{f}_{c}}-{{f}_{m}}\text{ }and\text{ }{{f}_{c}}+{{f}_{m}}\] are side band frequency \[{{f}_{c}}=250\times 10\] = 250 kHz Left Side Band \[=LSB={{f}_{c}}-{{f}_{m}}=2500250=~2250\text{ }kHz\] Right Side Band \[=RSB={{f}_{c}}+{{f}_{m}}\] \[=\text{ }2500+250\] \[=2750\text{ }kHz\] One new signal is of 250 Hz For this carrier wave should be taken in such a way that. LSB, RSB, fc do not overlap with previous frequencies. \[\therefore \,\,\text{ }{{f}_{c}}=2000\] as         \[LSB=1750\text{ }kHz\]             \[RSB=2250\text{ }kHz\] NTA has given answer but answer should be .


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