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Lecture Comments (3)

2 answers

Last reply by: Yukako Atsumi
Sat Aug 13, 2016 4:10 PM

Post by Yukako Atsumi on August 11 at 12:42:25 PM

Hi! In the other `wave characteristics` page, you said that the speed of sound in air at STP is approximately 343m/s?

Wave Characteristics

Lecture Slides are screen-captured images of important points in the lecture. Students can download and print out these lecture slide images to do practice problems as well as take notes while watching the lecture.

  • Intro 0:00
  • Question 1 0:23
  • Question 2 1:04
  • Question 3 2:01
  • Question 4 2:50
  • Question 5 3:12
  • Question 6 3:57
  • Question 7 4:16
  • Question 8 4:42
  • Question 9 4:56

Transcription: Wave Characteristics

Hi everyone and welcome back to 0000

I am Dan Fullerton and in today's mini-lesson, we are going to talk about wave characteristics, specifically by going through page 1 of the APlusPhysics worksheet on wave characteristics, which you can find the link for down below. 0002

Now, again, note that these are not AP level questions, but they will test your basic understanding to see if we are at least in the ballpark of where we need to go. 0015

So let us dive into question 1. 0022

What is the wavelength of a 256 Hz sound wave in the air at standard temperature and pressure? 0024

For this set of questions, we are going to be asked to assume that the velocity of sound in air at standard temperature and pressure is 331 m/s.0030

So what is the wavelength? 0041

Well if V = F(λ), then we know that λ wavelength = V/F or 331 m/s/256Hz = 1.29 meters, Answer Number 2. 0043

Number 2 -- The graph below represents the relationship between wavelength and frequency of waves created by two students shaking the ends of a loose spring. 0064

Calculate the speed of the waves generated in the spring. 0072

Well, we have a couple of different points we could use here, but all of these should follow our wave equation, V = F(λ), so I can solve here for (V) by picking a couple of points here. 0076

It looks like an easy point would be something like, frequency of 1 Hz and a wave length of 5 m, which would be 5 m/s. 0089

If I did that at any other point here on the curve too, this would be 2 × 2.5 or 5 or 2.5 × 2 or 5 or 5 × 1, again, is 5.0103

We have the same speed everywhere, which we should expect. 0113

So our speed must be 5 m/s. 0115

Number 3 -- What is the period of a water wave if 4 complete waves pass a fixed point in 10 s? 0121

Well, period is the time it takes for one wave, so if we have 10 s for 4 waves, that would be 10/4 or 2.5 s per wave. 0127

The correct answer is Number 3. 0139

You could also do this by looking at frequency first. 0141

Frequency is the number of cycles per second and if you go through 10 cycles or 4 waves, over 10 s, you are going to get a frequency of 0.4 Hz, then period is 1 over frequency or 1/0.4 Hz, which again, is 2.5 s. 0144

However you want to get there, 2.5 s is your best answer. 0163

Number 4 -- If the frequency of a periodic wave is doubled the period of the wave will be... 0171

Well, period is 1 over frequency. 0177

If you double the frequency, you have divided the right hand side by 2 and you have to take half the periods, so the correct answer to 4 must be Number 1. 0179

Number 5 -- A 512 Hz sound wave travels 100 m to an observer through air at standard temperature and pressure. 0192

What is the wavelength of the sound wave? 0200

Well, V = F(λ)... 0203

...which implies that λ wavelength is going to be V/F or 331 m/s/512 Hz (frequency), which is just going to be about 0.65 m. 0217

Number 6 -- The diagram below represents a periodic wave. 0236

Which point on the wave is in phase with point (P)? 0240

So there is (P) -- in phase means it is the same point on a corresponding wave, so (P) and (C) would be in phase, so correct answer there is Number 3. 0243

Number 7 -- A periodic wave having a frequency of 5 Hz and a speed of 10 m/s, has what wavelength? 0256

Well, if V = F(λ), then λ = V/F, which is 10 m/s/5 Hz or just 2 m, so the correct answer there is Number 2. 0263

Two more -- Number 8 -- A ringing bell is located in a chamber. 0280

When the air is removed from the chamber, why can the bell be seen vibrating, but not heard? 0285

Well, light waves can travel through a vacuum, but sound waves cannot.0289

Our last one -- The diagram below represents a transverse wave. 0294

The wavelength of the wave is equal to the distance between points. 0299

We need to find two same points on corresponding waves, so that would be (B) and (F) would work. 0303

That is one of our choices, Number 2, the distance between (B) and (F) would be 1 wavelength. 0310

All right, that concludes page 1 of the A+ Physics worksheet on wave characteristics.0316

If this went well -- Excellent -- keep moving on to the higher level questions, the AP level questions. 0320

If it did not go so well, now would be a great time to go back and review wave characteristics. 0325

Thanks so much for your time everyone and have a great day.0330