Wave problems to try.

Wave problems.

Some review questions (and a couple new ideas).

1. Differentiate between mechanical and electromagnetic waves. Give examples.

2. Draw a wave and identify (or just define) the following parts: crest, trough, amplitude, frequency, period.

3. Consider a wave that travels with a speed of 25 m/s and a wavelength of 5-m. What is the frequency of this wave?

4. Differentiate between longitudinal and transverse waves. Give examples. You may have to look this up, as we did not yet discuss it.

5. Draw the first 3 harmonics for a string that is 3-m in length. Also, find the first 3 wavelengths (using 2L/n) and frequencies (using f = v/l), if the wave speed is 100 m/s.

6. The speed of sound (in air) is approximately 345 m/s. If you stand far from a mountainside and yell at it, the echo returns to your ear in 1.8 seconds. How far is the mountain from you?

7. Approximately how much greater is the speed of light than the speed of sound in air?

8. Discuss the physics of the Chladni plate.

9. Find the wavelength of a 89.7 MHz radio wave.


More practice, to try after the next class:

1. Consider a 2-m long string fixed at both ends. The speed of wave travel is 200 m/s in this string. Find the following:

a. wavelengths of the first 3 harmonics
b. frequencies of the first 3 harmonics

(4, 2, 4/3 meters; 50, 100, 150 Hz)

2. Now imagine an organ pipe, 1-m long. The speed of sound (which is the same as the speed of wave travel in an organ pipe) is 340 m/s. Find the same things as above.

(2, 1, 2/3 meters; 170, 340, 510 Hz)

3. What is the effect of capping one end of a tube?

4. Consider a C note, vibrating at 262 Hz. Find the following frequencies:

a. the next C, one octave above this one
b. a C, two octaves above 262 Hz
c. the note C#, one piano key ("semi-tone") above C