What are the characteristics of mechanical and electromagnetic waves? Introduction to Waves What are the characteristics of mechanical and electromagnetic waves?

A. Rhythmic disturbances that carry energy without carrying matter I. What are Waves? A. Rhythmic disturbances that carry energy without carrying matter

B.Types of Waves 1. Mechanical Waves – need matter (or medium) to transfer energy a. A medium is the substance through which a wave can travel. (Air, water, particles, strings, solids, liquids, gases) 2. Electromagnetic Waves – DO NOT NEED matter (or medium) to transfer energy a. They do not need a medium, but they can go through matter (medium), such as air, water, and glass

C. Mechanical Waves Waves that need matter (medium) to transfer energy: a. Examples: Sound waves, ocean waves, ripples in water, earthquakes, wave of people at a sporting event

2. Transverse (Mechanical) Waves a. Energy causes the matter in the medium to move up and down or back and forth at right angles to the direction the wave travels. b. Examples: waves in water

a. Parts of a Transverse Wave The crest is the highest point on a wave.

Parts of a Transverse Wave The trough is the valley between two waves, is the lowest point.

Parts of a Transverse Wave The wavelength is the horizontal distance, either between the crests or troughs of two consecutive waves.

Parts of a Transverse Wave The amplitude is the peak (greatest) value (either positive or negative) of a wave. The distance from the undisturbed level to the trough or crest.

b. An ocean wave is an example of a mechanical transverse wave

3. Compressional Wave (longitudinal) A. A mechanical wave in which matter in the medium moves forward and backward along the same direction that the wave travels. Ex. Sound waves A slinky is a good illustration of how a compressional wave moves

b. Parts of a Compressional Wave (Longitudinal) The compression is the part of the compressional wave where the particles are crowded together.

Parts of a Compressional Wave (Longitudinal) The rarefaction is the part of the compressional wave where the particles are spread apart.

Parts of a Compressional Wave (Longitudinal) The wavelength is the distance from compression to compression or rarefaction to rarefaction in a compressional wave.

D. Period, Frequency, and Speed Wave frequency is the number of waves that pass a point in a unit of time The period of a wave is the time required for one complete cycle of vibration of the medium’s particles a. also describes the time it takes for a complete wavelength to pass a given point

3. Wave speed equals frequency x wavelength a 3. Wave speed equals frequency x wavelength a. the speed of a mechanical wave is constant for any given medium b. ex: at a concert, sound waves from different instruments reach your ears at the same time, so the speed is the same (frequencies and wavelengths may be different, but the product is the same at the same temp.)

c. when frequency is increased, wavelength must decrease for speed to remain constant d. The speed of a wave changes only when the wave moves from one medium to another or when the temperature or other certain properties of the medium are changed

E. Waves transfer Energy Waves transfer energy from one place to another without transferring the medium itself a. pebble in pond- waves move, but water remains in same place b. waves transfer energy by the vibration of matter, and can transport energy efficiently 2. Rate of energy transfer depends on amplitude: greater amplitude, more energy a wave carries a. for mechanical wave, energy transferred is proportional to square of amplitude b. double amplitude, energy increases 4x

II. Wave Interactions When objects in matter come together, they produce a collision 1. objects cannot occupy the same space at the same time, so they change their direction B. When 2 waves comes together, they don’t bounce back like objects 1. sound waves from different instruments are not affected by each other 2. mechanical waves are not matter, but are displacements of matter, so 2 waves can occupy the same space at the same time

C. Superposition- the combination of 2 overlapping waves 1 C. Superposition- the combination of 2 overlapping waves 1. interference pattern: 2 sets of waves in ripple tank pass through one another, interacting to form a pattern of light and dark bands a. this interference happens with visible light and other forms of E-M waves

2. Superposition principal: a 2. Superposition principal: a. when waves meet, they form a resultant wave b. the amplitude of the resultant wave is equal to the sum of the amplitudes of the two waves c. each wave maintains the same shape and direction it had before the waves met 3. Constructive interference: Displacements in the same direction produce this, are added together

4. Destructive interference: formed when the wave pulses are traveling toward each other in opposite directions a. displacements have different signs (+ and -) b. the resultant wave is the difference between them c. after the pulses separate, their shapes are unchanged d. complete destructive interference: 2 pulses of equal amplitude and opposite signs coincide, resultant wave has a displacement of zero (cancel each other

D. Reflection and Diffraction When a wave reaches a boundary, it bounces off the boundary and is sent back (reflection) 2. When a wave changes its direction as it encounters an obstacle, opening or edge (p 532)

E. Standing Waves A wave pattern that results when 2 waves of the same frequency, wavelength, and amplitude travel in opposite directions and interfere a. consists of alternating regions of constructive & destructive interference b. pattern appears to be a stationary wave 2. Have nodes-points at which complete destructive interference occur, no motion 3. Have antinodes- point where largest displacement occurs, half way point between nodes (Chapter ends here)

Electromagnetic Waves Waves that DO NOT NEED matter (medium) to transfer energy Examples: radiation, TV & radio waves, X-rays, microwaves, lasers, energy from the sun, visible light Electromagnetic waves are considered transverse waves because they have similar characteristics; therefore, they have the same parts. More to come on Electromagnetic waves…

Electromagnetic Spectrum The electromagnetic spectrum illustrates the range of wavelengths and frequencies of electromagnetic waves.

Electromagnetic Spectrum Sheet

Types of Waves Quad Clusters Summarizing Strategy Types of Waves Quad Clusters