Physics 11 An Introduction to Waves and Sound

Definition of a Wave Waves: a disturbance or vibration that transfers energy progressively from point to point in a medium.

Types of Waves Mechanical Waves: require a material medium. (Ex. Water waves, sound waves, waves in springs or ropes) Electromagnetic Waves: require no material medium. (Ex. Light waves, radio waves and x-rays) Matter Waves: Particles of matter “wave” when moving. (Quantum mechanics is needed to describe these waves. Electrons and other particles show wave-like behavior under certain circumstances)

Mechanical Waves two main types of mechanical waves. Transverse Waves Wave (Energy) Movement Crest/Peak Particle Movement Valley/Trough

Types of Mechanical Waves Transverse Waves Click here to view a propagating transverse wave. Key Features: Particles move UP and DOWN Wave energy propagates (moves) forward at a very specific speed. The wave speed is dependent on the type of material (or medium) that the wave is traveling through not on the amount of energy or amplitude (size) of the wave.

Types of Mechanical Waves Transverse Waves (The Wave)

Mechanical Waves Longitudinal Waves (Compression Waves) Wave (Energy) Movement Compression Particle Movement Rarefaction

Types of Mechanical Waves Longitudinal Waves Click here to view a propagating longitudinal wave. Key Features: Particles move SIDE to SIDE Wave energy propagates (moves) forward at a very specific speed. The wave speed is dependent on the type of material (or medium) that the wave is traveling through not on the amount of energy or amplitude (size) of the wave.

Speed of Waves Heavy medium  slower speed Speed of wave is dependent on the properties of the medium through which it is travelling. Heavy medium  slower speed Lighter medium  faster speed Increased tension  faster speed Amplitude  does not affect speed No real difference in speeds between Transverse and Longitudinal wave

Waves At Boundaries Between Media Waves can move (transfer) from one Medium into another medium. What happens to the energy as the wave passes from one medium into another medium? What happens to the speed and size of the wave?

Transmission and Reflection Two things happen when a wave reaches a boundary 1. Part of the energy is transmitted into the medium (Transmitted Wave) 2. Part of the energy moves backward from the boundary (Reflected Wave)

Waves at Boundaries…continued When the medium changes, wave energy is both reflected and transmitted. Two Cases: 1. Difference in media is small: most of the energy will transmit. 2. If the two media are very different: most of the energy will be reflected.

Important Question Is the reflected wave INVERTED or ERECT? Whenever a wave passes from a less dense to a more dense medium, the reflected wave is inverted. When a wave passes from a more dense to a less dense medium, the reflected pulse is erect, not inverted.

Superposition of Waves Principle of Superposition: “The displacement of a medium caused by two or more waves is the algebraic sum of the displacements caused by the individual waves.” Physics: Principles and Problems, Merrill, 1992

Interference When two or more waves interact with one another it is called interference. There are two types of interference: CONSTRUCTIVE INTERFERENCE: When wave displacements are in the same direction the result is a wave that has a larger amplitude than either of the original waves. Click Here! DESTRUCTIVE INTERFERENCE: If the wave displacements are in opposite directions the result is a wave with a smaller amplitude Than the individual waves. Click Here!

References Animated waves are compliments of: Dr. Dan Russel of Kettering University – Applied Physics http://www.gmi.edu/~drussell/Demos/reflect/reflect.html