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9th Class Science Sound Question Bank Sound Formative Objective Problems

  • question_answer
    Calculate the wavelength of radio waves of frequency\[\text{1}{{0}^{9}}\text{Hz}\]. The speed of radio waves is \[\text{3}\times \text{1}{{\text{0}}^{8}}\text{m}/\text{s}.\]

    A)  20 cm                                  

    B)  35 cm

    C)  30 cm                  

    D)  25 cm

    Correct Answer: C

    Solution :

                      \[\lambda =?,\] \[f={{10}^{9}}Hz,\text{ }v=3\times {{10}^{8}}m/s\] We know, \[V=f\lambda \] \[\Rightarrow \] \[\lambda =\frac{V}{f}=\frac{3\times {{10}^{8}}}{{{10}^{9}}}m=\] \[3\times {{10}^{-1}}m=0.3m=30\,cm\]


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