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Awhistle of frequency 540 Hz rotates in a circle of radius 2 m at a linear speed of 30 m/s. What is the lowest and highest frequency heard by an observer a long distance away at rest with respect to the centre of circle. Take speed of sound in air as 330 m/s. Can the apparent frequency be ever equal to actual? |
Answer» Solution :Apparentfrequency will be MINIMUM whenthe source is at N and moving AWAY from the observer. `f_("min") + (v/(v +v_s)) f =(330/(330 +30)) xx 540 = 495 Hz` FREQUENCY will be maximum when source is at L and approachign the observer. `f_(max) =(v/(v-v_s)) f = (330/(330 -30)) (540) = 594 Hz` Further when source is at M and K, angle between velocity of source and line joining source and observer is `90^@" or " v_s cos theta =v_s cos 90^@ =0`. So, there will be no change in the apparent frequency. i.e., no Doppler effect. |
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