1. Aim: Practice Wave Problems
HW: Problem Set

2. A person with his ear to the ground, sees a huge stone strike the concrete pavement. A moment later the two sounds are heard from impact.
Explain which is heard first and why?
The two sounds are heard 1.1 s apart and the speed of sound in concrete is 2950 m/s.
How far away was the impact?

3. Solution
V = f x λ …. This is the same as V = d/t In air: 331 m/s = d/t In concrete: 2950 m/s = d/(t-1.1s) 331t = 2950t t = 1.24 s (accounts for quicker time in concrete) D ≈ 410 m

4. Strings and Pipes
String fixed at both ends or a pipe open at both ends.
String fixed at one end or a closed pipe.

5. What else affects the velocity of a wave caused by a STRING???
String Tension
String Mass
String Length
How do you think each one affects velocity from an intuitive standpoint?
This should NOT be memorized but recognized!

6. Station Activity
Attempt the following 2 stations.

7. The following is a position vs. time graph for a oscillating pendulum.
What are the points of Max KE and Max PE?
How does the mechanical energy of the system change from start to finish?

8. Open Pipes
If you were to build a pipe organ with open-tube pipes spanning the range of human hearing (20Hz – 20kHz) what would be the range of the lengths of pipes required?
Lowest Frequency: 8.3 m
Highest Frequency: 8 mm

9. Wave Properties
Which of the following waves can be transmitted through space? Justify your answer.
Visible Light
Radio Waves
Gamma Rays
Sound Waves
(i), (ii), and (iii) are all electromagnetic and transverse waves traveling with speed “c”.

10. Group Activity
A pipe is closed at one end and a tuning fork with frequency 245 Hz will cause the pipe to resonate for a minimum length of 34 cm.
What are 3 additional lengths to cause resonance?
The end of the pipe is now opened. Describe the changes in length that would occur for resonance with the fork.
The air is replaced with helium. Describe an experiment that would use the pipe to determine the speed of sound in helium.
66 cm, 110 cm and 154 cm
The minimum length would be 44 cm, with other possible lengths as multiples of 44 cm
Using the same fork with frequency 245 Hz, we can assume f is constant, so according to V = f x wavelengths all we need to do is test out different lengths until we find the shortest possible pipe for resonance.