Mechanical (sound) waves are unable to travel through a vacuum, such as through space, but radio waves are transmitted to earth from satellites. how is this possible?

What is the frequency of a light wave with a wavelength of 620nm

The intensity, or loudness, of a sound can be measured in decibels (db), according to the equation , where i is the intensity of a given sound and is the threshold of hearing intensity. what is the intensity, in decibels, [i(db)], when ? use a calculator. round to the nearest whole number. 8 9 19 80

What are similarities and differences of reflection, refraction, diffraction and absorption?