WAVES PROPERTIES Chapter 11, Section 3

What is a wave? A wave is a disturbance that carries energy through matter or space.

Most waves travel through a medium A medium is matter which means it is composed of particles. Examples of mediums are water and air. It can also be solids such as a slinky or rope. Waves that require a medium to travel are called mechanical waves.

Electromagnetic waves do not require a medium. can travel through space without the presence of matter. can travel through space without the presence of matter. consist of changing electric and magnetic fields. consist of changing electric and magnetic fields.

Types of waves A wave that consists of a single traveling pulse is called a pulse wave. A wave that consists of a single traveling pulse is called a pulse wave. A group of pulse waves form a periodic wave. A group of pulse waves form a periodic wave. A wave whose source vibrates with a simple harmonic motion is called a sine wave. A wave whose source vibrates with a simple harmonic motion is called a sine wave.

Longitudinal Waves Waves that cause particles in a medium to vibrate parallel to the direction of wave motion. Waves that cause particles in a medium to vibrate parallel to the direction of wave motion. Examples: Sound waves Examples: Sound waves s/waves/wavemotion.html s/waves/wavemotion.html s/waves/wavemotion.html s/waves/wavemotion.html

Transverse Waves Waves in which the motion of the particles is perpendicular to the motion of the wave as a whole. Waves in which the motion of the particles is perpendicular to the motion of the wave as a whole. Examples: Light waves Examples: Light waves emos/waves/wavemotion.html emos/waves/wavemotion.html emos/waves/wavemotion.html emos/waves/wavemotion.html

Wave Properties Crest – the highest point of a transverse wave. Crest – the highest point of a transverse wave. Trough – the lowest point of a transverse wave. Trough – the lowest point of a transverse wave. Amplitude – the greatest distance that particles in a medium move from their normal position when a wave passes. Amplitude – the greatest distance that particles in a medium move from their normal position when a wave passes. Wavelength – the distance between any two successive identical parts of a wave. Wavelength – the distance between any two successive identical parts of a wave.

Wave Properties Diagram Wavelength crest amplitude trough

Period & Frequency Period – time required for one full wavelength to pass a certain point. Period is measured in seconds (s). Period – time required for one full wavelength to pass a certain point. Period is measured in seconds (s). Frequency – the number of vibrations that occur in one second. Frequency is measured in Hertz (Hz). Frequency – the number of vibrations that occur in one second. Frequency is measured in Hertz (Hz).

Equation for Period & Frequency f = frequency (Hz) T = period (s) f = 1 / T T = 1 / f

Practice Problem 1) 20 waves passed in 10 seconds. What is the frequency and period of the wave? f = 2 Hz T = 0.5 s

2) What is the frequency of a wave if it takes 0.25 s for one wave to pass a certain point? f = 4 Hz Practice Problem

3) A wave has a frequency of 260 Hz. How long does it take for one of these waves to pass a specific point in a medium? T =.0038 s Practice Problem

4) A boy is floating in the ocean near the beach. In 25 s, 5 big waves have passed over the boy. What is the frequency and period of these waves? f = 0.2 Hz T = 5 s Practice Problem

Relating frequency to wavelength The longer the wavelength, the lower the frequency. The longer the wavelength, the lower the frequency. The shorter the wavelength, the higher the frequency. The shorter the wavelength, the higher the frequency.

Relating Frequency & Period The higher the frequency, the shorter the period. The higher the frequency, the shorter the period. The lower the frequency, the longer the period. The lower the frequency, the longer the period.

Amplitude does not affect the wavelength or frequency High amplitude Low amplitude

Pitch & Frequency The higher the frequency, the higher the pitch. The higher the frequency, the higher the pitch. The lower the frequency, the lower the pitch. The lower the frequency, the lower the pitch.

Wave Speed How fast a wave travels. How fast a wave travels.

Speed depends on the medium. Sound travels through the air at an average speed of 340 m/s. In gases, the molecules are far apart and move around randomly. A molecule must travel through a lot of empty space before it bumps into another molecule Sound travels through the air at an average speed of 340 m/s. In gases, the molecules are far apart and move around randomly. A molecule must travel through a lot of empty space before it bumps into another molecule

Speed depends on the medium. In water, sound travels 3-4 times faster than it would in air. In liquids, molecules are much closer together and free to slide past one another. In water, sound travels 3-4 times faster than it would in air. In liquids, molecules are much closer together and free to slide past one another.

Speed depends on the medium. In a rock or metal, sounds travels 15 – 20 times faster that it would in air. In a solid, molecules are tightly bound to each other. When one molecules starts to vibrate, all the others start to vibrate almost immediately. In a rock or metal, sounds travels 15 – 20 times faster that it would in air. In a solid, molecules are tightly bound to each other. When one molecules starts to vibrate, all the others start to vibrate almost immediately.

Light has a finite speed. Light travels much faster than sound which is 3 x 10 8 m/s (186,000 miles per second). Light travels much faster than sound which is 3 x 10 8 m/s (186,000 miles per second). Light travels slower when it has to go through a medium such as air or water. Light travels slower when it has to go through a medium such as air or water.

Doppler Effect An observed change in the frequency of a wave when the source or observer is moving. An observed change in the frequency of a wave when the source or observer is moving.

Doppler Effect Explanation When a moving sound source moves away from you, the wavelength near you gets longer. The longer the wavelength, the lower the frequency which causes you to hear a lower pitch. When a moving sound source moves away from you, the wavelength near you gets longer. The longer the wavelength, the lower the frequency which causes you to hear a lower pitch.

Doppler Effect Explanation When a moving sound source moves towards you, the wavelength near you gets shorter. The shorter the wavelength, the higher the frequency which causes you to hear a higher pitch. When a moving sound source moves towards you, the wavelength near you gets shorter. The shorter the wavelength, the higher the frequency which causes you to hear a higher pitch.

Calculating the Velocity of a Wave v = speed / velocity (m/s) v = speed / velocity (m/s) λ = wavelength (m) λ = wavelength (m) Equations: Equations: v = f λv = λ/T

Practice Problems 1) 1.50 m/s 2) 3 x 10 8 m/s 3) 5.77 x Hz 4) 1.5 m