• # question_answer If the quartz plate is vibrating is 3rd harmonic while measuring the frequency of 1.2 x 106 Hz, then the thickness of the plate is A)  71.75 cm                    B)  7.175 cm         C)  6.02 cm          D)  0.07 cm

For 3rd harmonic, $f=3{{f}_{0}}=1.2\times {{10}^{6}}$ ${{f}_{0}}=\frac{2.87\times {{10}^{4}}}{s}=1.2\times {{10}^{6}}$ or       $s=0.07175\,\,cm$