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Homework Help: Frequency of microwaves

  1. May 30, 2006 #1
    1)Microwaves are directed normally at a plane metallic reflector. A detector moving along the normal to the reflector travels 15 cm from the first to the 11th successive of minimum intensity. What is the frequency of the microwave?(velocity of microwaves = 3 x 10^8 m/sec)
    I solved it in the following way:
    The incident and the reflected microwaves superimpose to produce standing waves. The distance between the first and the 11th minimum is given that it is 15 cm.
    0.15 = 10 x (lambda/2)
    Lambda = 0.03 meters
    Frequency = (3 x 10^8)/ 0.03
    = 10^10 Hz
    Is it right?
    2)Two waves of same frequency travel in opposite directions in a medium with amplitudes 3 units and 2 units respectively. What is the ratio of the amplitudes at an antinode and a node in the stationary wave?
    I think it is infinity because at the antinode it has maximum amplitude and at the node it is zero. Is it right?
  2. jcsd
  3. May 30, 2006 #2


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    Staff Emeritus
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    This looks good to me. Just a small point however, using standard scientific notation it is better to quote the answer as 1x1010 Hz. However, both are correct.

    Are you sure about that? The formal definition of a node is "a point of minimum displacement.", this need not to be zero. The important thing to note is the respective amplitudes, try sketching the two waves in anti-phase on the same graph.

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