Waves

Frequency is the number of complete cycles in a given time.Frequency is measured in cycles per secondor hertz (Hz).

1FUN FACT:

Hertz is named after Heinrich Hertz (1857 to 1894)-- not the car company!

Do not have the students take notes over this slide. It is just interesting information.2Turn to a partner:What determines the frequency of a wave?

3Turn to a partner -- answerWhat determines the frequency of a wave?Answer: The number of complete cycles.

4The time required for one cycle is called the time period. unit -- second

5A wave vibrating at one cycle per second has a frequency of 1.0 Hz.

A wave vibrating at two cycles per second has a frequency of 2.0 Hz.Second & Hertz how they are connected

Frequency = 1.0 hertzOne cycle per secondFrequency = 2.0 hertzTwo cycles per second6Wavelength and Frequency RelationshipIf you assume that waves are traveling at a constant speed, then wavelength is inversely proportional to frequency.Increasing the frequency of a wave decreases its wavelength.

7Wave Velocity Equationvelocity = wavelength frequency V = fv f

8The next slide will have the students going through the 3 equations with this triangle.Turn to a partner and writedown the three equations using this trianglev f

9Go through the triangle with the studentsV = ff = v = v f(This is very similar to what they learned with motion.)Turn to a partner and writedown the three equations using this triangle -- answerv f V = f

f = v

= v f

10Go through the triangle with the studentsV = ff = v = v f(This is very similar to what they learned with motion.)When the velocity is constant if the wavelength increases then the frequency will decrease. RelationshipsV = f

11Speed of Mechanical WavesOne end of a rope vibrates to produce a wave with a wavelength of 0.25 meter. The frequency of the wave is 3.0 hertz. What is the speed of the wave?Hint: Hz = 1/s

Modeled Practice

12Speed of Mechanical Waves -- answerOne end of a rope vibrates to produce a wave with a wavelength of 0.25 meter. The frequency of the wave is 3.0 hertz. What is the velocity of the wave? Hint: Hz = 1/sGivens: 0.25 m = 3.0 hertz = fUnknown: v Equation: V = fPlug in numbers: v = (0.25 m)(3.0 Hz)(Units involved) (0.25 m)(3.0 1/s)Answer: 0.75 m/s

13Remind students that a Hz is 1/s so that the second will be on the bottom.Turn to a partner: Is your answer reasonable?

14Is your answer reasonable? -- answer

Because the frequency is 3.0 hertz, the wave should travel a distance of 3 wavelengths in 1 second. This distance is 0.75 meters, which agrees with the calculated speed of 0.75 m/s.

15What is the wavelength of an earthquake wave if it has a velocity of 5,000 m/s and a frequency of 10 Hz?

Small Group:

16Partner Practice AnswerWhat is the wavelength of an earthquake wave if it has a velocity of 5,000 m/s and a frequency of 10 Hz? Hint: Hz = 1/sGivens: 5,000 m/s = v 10.0 hertz = fUnknown: Equation: = v fPlug in numbers: = (5,000 m/s) (10 1/s)Answer: = 500 m

17A wave on a rope has a wavelength of 2.0 m and a frequency of 2.0 Hz. What is the speed of the wave?

Individual Practice

18Individual Practice AnswerA wave on a rope has a wavelength of 2.0 m and a frequency of 2.0 Hz. What is the speed of the wave? Hint: Hz = 1/sGivens: 2.0 m = 2.0 hertz = fUnknown: v Equation: V = fPlug in numbers: v = (2.0 m)(2.0 Hz)(Units involved) (2.0 m)(2.0 1/s)Answer: 4 m/s

19Sound waves are longitudinal waves Sound Waves

20In general, sound waves travel fastest in solids, slower in liquids, and slowest in gases.The speed of sound depends on many factors, including the density of the medium and temperature.Properties of Sound Waves

21Remind them:Particles in a solid tend to be closer together than particles in a liquid or a gas.

FUN FACTUltrasound is used in a variety of applications, including sonar and ultrasound imaging.

Most people hear sounds between 20 hertz and 20,000 hertz. Ultrasound is sound at frequencies higher than most people hear.22The students do not need to put this slide in their notes.Small Group:Discuss when you would need an ultrasound.

23Ultrasound can be used to make images of the heart to see how your heart beats.Small group:Discuss when you would need an ultrasound. -- answer

24This is one possible answer. Stress this is used for any soft organ.Sound energy is recorded by converting sound waves into electronic signals (electrical energy) that can be processed and stored.

Sound is reproduced by converting electronic signals back into sound waves.

25Exit Questions - Day 11. Name the different parts of the given wave diagram.

2. How many waves are there in the diagram shown above?

The key is on the next slide.26EXIT QUESTION Day 11. Name the different parts of the given wave diagram.Answer:

2. How many waves are there in the diagram shown above?Answer: one and a half wave = 3/2

HOMEWORK 2. Wave worksheet #1