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Physics 16-17
| Question | Answer |
|---|---|
| Mechanical Waves | Require a medium to travel, like water waves need water. |
| Transverse Waves | The particles of the medium move at right angles to the direction of the wave. |
| Crest & Trough | The top part of the wave is called the crest while the part of the wave below the equilibrium is called the trough. |
| In a distance vs. vertical position graph, you can find... | The lamdba (wavelength) which is the distance in between crests. You can also find the amplitude (distance between the midline vs the crest or trough). |
| In a time vs. vertical position graph, you can find... | The period (distance between the crests, a full cycle) and the frequency (as an extension of the period). You can also find the amplitude again. |
| Things to remember about the mathematical wave equation (3rd in the waves and sound section) | When wave motion is through positive x, there's a minus sign and when wave motion is through neg x, there's a plus sign. The 2pifT portion is equivalent to wt and can be replaced by it. |
| Rope Equation | Can be put into place when the rope is very stretched and the amplitude is very small. v = square root of (FT/(m/L)). Where FT is the tension in the string and m/L is the mass per unit length of the string. |
| Speed of Sound in a gas is proportional to the temperature. This is the equation you'll use: | V = 331 + 0.6T m/s (T has to be in celsius!) |
| Sound Intensity Equation | I = P/A P = Power A = Area |
| Sound generated in all directions equation | Ptotal / 4pir^3 Power / surrounding area of the source |
| Io | Threshold Intensity |
| Ip | Pain Intensity |
| Tip about sources and power | If you double the number of sources, you double the power, which will in turn double the intensity. |
| Tip about intensity and factors | When the number of sources is increased by a factor, the decibel (beta) does increase by the same amount. It increases according to the log equation. |
| Log (a*b) = | Log(a) + Log(b) |
| Log(a/b) = | Log(a) - Log(b) |
| 10Log10(I1/I0) can also be written as... | B1 |
| Tip about the power of ten | If the number of sources increases by the power of ten, then... 100 = 10^2 -> inc is 10*2 = 20 db 10,000 = 10^4 -> inc is 10*4 = 40 db 1,000,000 = 10^6 -> inc is 10*6 = 60 db |
| Doppler Effect | Refers to the movement of a source and a listener; equations are provided in the reference sheet. When you are moving towards a source, the velocity of the sound increases & away, decreases. When you are moving towards, wavelength is shorter & away, long |
| Tip about Wavelength & Source | When you have a stationary source, the wavelength does not change. |
| When you are trying to find the amount of n, do this... | Remember that In = n * I1. Set up equation as Bn = 10Log10(n) + B1, then continue until you have Log10(n) = x. You can do n = 10^x and get your answer that way. |
| Tips for finding the max and min frequencies | When they are asking you to find the difference in max and min frequencies, you can subtract the listener moving towards (+) by listener moving away. You can find vo like this and know that vmax = aw. Like this, you can also find a & w & T. |
| Constructive Interference | happens when two or more waves overlap at the same point in space. Amplitudes add and lead to a max amp. Usually in phase. |
| Destructive Interference | occurs when waves arrive out of phase. Amplitudes cancel, no amp at total overlap. Usually out of phase. |
| In phase | two waves line up crest-to-crest and trough-to-trough so they add together. |
| Out of phase | a crest lines up with a trough so they cancel. Tends to have a difference of half a wavelength. |
| In Phase + Constructive & Destructive | If the difference in distance is a whole number of wavelengths, the waves arrive in sync and add → loud sound. If the path difference is an odd half-wavelength, one wave arrives as a crest and the other as a trough → they cancel (quiet spot). |
| Out of Phase + Constructive & Destructive | (Speakers are already 180° off). The extra half-wavelength travel undoes the initial mismatch, so the waves line up again → loud sound. A whole-wavelength path difference keeps the waves out of sync, so crest meets trough → cancellation. |
| When it asks you what are the three lowest frequencies (or something along that line)... | you just have to keep putting integers in. If it says three lowest frequencies at which you hear no sound, you should immediately understand that it's referring to destructive interference. |
| Diffraction | Diffraction is the spreading of a wave after it passes through an opening. The smaller the opening compared to the wavelength, the more the wave spreads. Equations are given on the sheet. |
| Name of 1st Harmonic | Fundamental |
| Name of 2nd Harmonic (3rd for Odd) | 1st Overtone |
| Name of 3rd Harmonic (5th for Odd) | 2nd Overtone |
| Standing Wave Formulas... | All provided on the exams sheet. |
| Node | point that never moves, Caused by complete destructive interference, Fixed ends of strings are always nodes |
| Anti-Node | point that moves the most, Caused by constructive interference, Occurs halfway between nodes |
| Distance between two adjacent nodes | 𝜆/2 |
| Distance between node and nearest antinode | 𝜆/4 |
| Harmonics | The wave must place nodes at fixed points (like string ends). These allowed wavelengths are called harmonics |
| Important Formula for Velocity in this chapter | velocity = lamdba * frequency |
| Beats | Two waves of equal amplitude but slightly different frequencies traveling in the same direction give rise to beats. Beats are the max and min sound. |
| Tip about Frequency & Oscillations | The one with the lower frequency completes less oscillations in a period. |
| How to figure out which tuning fork has what frequency when there's a mass attached? | If you sound two forks with the same frequency together, you won't hear a sound. But if you attach playdoh to one, there will be a beat freq of 2. If the og amount was 440 Hz, it will be 438 on the playdoh fork, because it's vibrating at a lower freq. |
| Important Equation that can help you figure out if you have constructive or destructive interference | Delta L / lambda = n |
Created by:
smurtab