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

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

Turn to a partner: What determines the frequency of a wave?

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

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

A. A wave vibrating at one cycle per second has a frequency of 1.0 Hz. B. A wave vibrating at two cycles per second has a frequency of 2.0 Hz. Second & Hertz – how they are connected Frequency = 1.0 hertz One cycle per second Frequency = 2.0 hertz Two cycles per second

Wavelength and Frequency Relationship If 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.

Wave Velocity Equation velocity = wavelength × frequency V = λ × f v f λ

Turn to a partner and write down the three equations using this triangle v f λ

Turn to a partner and write down the three equations using this triangle -- answer v f λ V = λ × f f = v ÷ λ λ = v ÷ f

When the velocity is constant – if the wavelength increases then the frequency will decrease. Relationships V = λ × f

Speed of Mechanical Waves One 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

Speed of Mechanical Waves -- answer One 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/s Givens: 0.25 m = λ 3.0 hertz = f Unknown: v Equation: V = λ × f Plug in numbers: v = (0.25 m)(3.0 Hz) (Units involved) (0.25 m)(3.0 1/s) Answer: 0.75 m/s

Turn to a partner: Is your answer reasonable?

Is 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.

What 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:

Partner Practice – Answer What 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/s Givens: 5,000 m/s = v 10.0 hertz = f Unknown: λ Equation: λ = v ÷ f Plug in numbers: λ = (5,000 m/s) ÷ (10 1/s) Answer: λ = 500 m

A 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

Individual Practice – Answer A 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/s Givens: 2.0 m = λ 2.0 hertz = f Unknown: v Equation: V = λ × f Plug in numbers: v = (2.0 m)(2.0 Hz) (Units involved) (2.0 m)(2.0 1/s) Answer: 4 m/s

Sound waves are longitudinal waves Sound Waves

In 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

FUN FACT Ultrasound 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.

Small Group: Discuss when you would need an ultrasound.

Ultrasound 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

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.

1. Name the different parts of the given wave diagram. 2. How many waves are there in the diagram shown above?

1. 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 λ

HOMEWORK – 2. W AVE WORKSHEET #1