11/7/2023 0 Comments Night beach sounds![]() With this temperature gradient, you can calculate that a ray which starts off horizontally will bend over 4 meters downwards as it travels forwards 1 kilometer. That's a rapid change if you go skydiving, you will be a great deal colder in the air, and you can feel the temperature change in real time as you fall. In real life, the temperature in the atmosphere typically falls about 5 degrees for each kilometer you go upwards. In reality, every ray of sound in this situation bends downwards in a curved path, and rays closest to the horizontal bend the most. ![]() Now, I couldn't find any actual scientific papers on this topic, and most of the websites online were completely wrong (for example, the explanation here: is NOT what happens). Since the observer is on the earth, towards which the sound rays are bending, the argument is that you will hear more of the sound than you would without the temperature gradient. Similarly, in the atmosphere it causes the sound waves to bend downwards, towards the earth. This "gradient index" is well-known in optics, where it can be used to make a lens to bend light rays. For example, if the air near the ground is cool, and the air above it is warmer, then the index of refraction decreases with height. ![]() The argument usually involves a temperature gradient. However, I have heard qualitative arguments for why sounds could actually be louder at night or in the morning. But when we are lying in bed trying to sleep, and everything is quiet, the train seems especially disturbing. During the day, there are more other sounds that we focus on, and our minds are often distracted with whatever we happen to be doing at the moment, so we don't tend to notice the sound of, say, a train. Now, how do we explain why sounds often sound louder at night than during the day? I am pretty sure the reason for this effect is psychological. The overall effect is that the index of refraction in the glass now varies sinusoidally (like the sound wave), and light is caused to scatter (sort of like a diffraction grating). At points where the pressure from the sound wave is large, the index of refraction is increased slightly (since the medium is more dense), and where the pressure is small, the index decreases slightly. For example, acousto-optic modulators (aka Bragg cells) use standing sound waves inside glass to induce index of refraction shifts. That gives a literal meaning to the phrase "noisy signal"! In other cases, we can use this effect for engineering. For example, sound waves can cause mirrors to vibrate in sensitive optics experiments, thus messing up the data. I should point out, though, that sound can affect light, even if it doesn't happen the other way around. The electric and magnetic fields associated with typical light beams are much smaller than those from a capacitor or a magnet, so if you wanted them to somehow interact with the vibration of particles in a sound wave, you'd probably need a huge laser pointed at the material through which sound was passing. Įven if light weren't so fast, it's hard to see exactly how light could affect sound. Now, the timescale (for example, the oscillation speed or the wave speed) for light is much faster than that for sound, so sound doesn't even notice when light is around.Ī similar example of a "timescale argument" can be found here. Light is made of vibrations in the electric and magnetic fields. Sound is made of vibrations (aka rapid pressure fluctuations) in air, water, or solid material. "Disclosure: Some of the links in this post are "affiliate links." This means if you click on the link and purchase the item, we will receive a small affiliate commission.Light does not really affect sound. ► YouTube Membership - /FTUSYouTubeMembership ![]() ► All In One Bundle - ► Our Bandcamp Full Discography - /FTUSBandcamp ► License Agreement - /FTUSlicenseagreement ► Our website - ► How to download all libraries on BC - /howtodownload
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