It is observed that amplitude modulated (AM) radio wave shows appreciable diffraction when it encounters an opening of size 75 cm `xx` 75 cm. In such a case, diffraction shown by frequency modulated (FM) wave is very negligible. If `lambda_A and lambda_F` represent average wavelengths of AM and FM waves, then

Options

A. `lambda_A lt lambda_F`
B. `lambda_A gt lambda_F`
C. `lambda_A ~~ lambda_F`
D. information is not sufficient to decide any relation between wavelengths

Answer

B

Explanation

For an appreciable diffraction the size of the opening should be of the order of the wavelength. FM wave does not show appreciable diffraction, hence its wavelength must be much smaller than opening and for AM wave it should be of the order of the opening . Hence we can say that wavelength of AM wave must be greater than wavelength of frequency modulated wave.