Chapter 14 and 15

Section 1: Types of Waves What is a Wave? A wave is a periodic disturbance in a solid, liquid, or a gas as energy is transmitted through a medium. A wave carries energy through matter and space. Waves transfer Energy – can do work on objects. Ex: seismic waves, water waves, light, sound A medium is the physical environment (matter) in which the wave travels through.

Section 1: Types of Waves

Section 1: Types of Waves Two Types of Waves Mechanical Waves – a wave that requires a medium to travel. sound Electromagnetic Wave (EM) – a wave that does not require a medium A wave that consists of oscillating electric and magnetic fields, which radiate outward at the speed of light. Light waves

Section 1: Types of Waves Energy may spread out as a waves travels Most waves are caused by vibrating objects. EM waves are caused by vibrating particles. Mechanical waves cause particles in the medium to vibrate as the wave passes through them.

Section 1: Types of Waves Vibrations involve transformations of Energy. Pull weighted spring and store EPE then let go EPE is converted to KE and then back to EPE (GPE) and back to KE then back to EPE. Simple harmonic motion

Section 1: Types of Waves

Section 1: Types of Waves Connect many weighted springs together only pull the first one and can transfer energy to rest of springs. A wave can pass through a series of vibrating objects Damped harmonic motion

Section 1: Types of Waves

Section 1: Types of Waves Transverse and Longitudinal Waves Two wave forms (classes) Based on direction the particles in the medium move as the wave passes. 1) Transverse Wave – particle motion is perpendicular to direction of the wave. Up and down 2)Longitudenal Wave – (compressional wave) particle motion is parallel with the wave motion. Back and forth

Section 1: Types of Waves

Section 1: Types of Waves Surface Wave Combination of transverse and longitudinal waves at the boundary of two mediums. Moves particles in a circular motion.

Section 1: Types of Waves

Section 2: Characteristics of Waves Wave Properties Transverse waves – S shape called sine waves. Crest – highest point Trough – Lowest point Amplitude – maximum distance that the particles of a wave’s medium vibrate from their rest position. Larger the amplitude – more the energy the wave carries. Wavelength – measures the distance b/w two equivalent parts of a wave. Crest to crest or trough to trough

Section 2: Characteristics of Waves

Section 2: Characteristics of Waves Longitudinal waves Compression – crowded area of particles. Equivalent to crest Rarefaction – area of spaced out particles. Equivalent to trough. Wavelength – measures the distance b/w two equivalent parts of a wave. Compression to compression or rarefaction to rarefaction Amplitude of Longitudinal waves is related to how tightly the medium is pushed together at the compression

Section 2: Characteristics of Waves

Section 2: Characteristics of Waves Wavelength represented by Greek letter Lambda or λ. SI unit is meter. Period – measures how long it takes for waves to pass by. Time it takes for one full wavelength of a wave to pass a certain point. Symbol is T SI unit is seconds

Section 2: Characteristics of Waves

Section 2: Characteristics of Waves Frequency – measures the rate of vibrations # of full wavelengths that pass a point in a given time interval. Measures how rapidly vibrations occur in the medium, at the source of the wave, or both. Symbol is f SI unit is the Hertz or Hz = 1/s = Waves/s

Section 2: Characteristics of Waves Formula: Frequency = 1 / period Frequency and period are inversely proportional.

Section 2: Characteristics of Waves Wave Speed velocity = wavelength times frequency SI unit is m/s

Section 2: Characteristics of Waves

Section 2: Characteristics of Waves Factors that affect wave speed. Speed of wave depends on the medium. Kinetic Theory of Matter explains differences in wave speed. Gases – waves do not travel fast – particles too spread out. Liquid – molecules closer together – vibrations transfer more quickly. Solid – waves travel very quickly – molecules most compact and energy is transferred more easily.

Section 2: Characteristics of Waves Light has a finite speed All EM waves in empty space travel at same speed. Speed of light = 3.00 x 108 m/s or 186,000 miles/s Symbol is c Moves slower in air, water, and other medium.

Electromagnetic Spectrum Light comes in a wide range of wavelengths and frequency Increase Frequency – Decrease Wavelength Called the Electromagnetic spectrum Frequency proportional to energy. Higher the frequency Higher the energy.

Section 2: Characteristics of Waves Doppler Effect Pitch is determined by the frequency of sound wave. Pitch is how high or low the sound is. High frequency = high pitch

Section 2: Characteristics of Waves Frequency changes when the source of waves is moving. Moving toward Wave is compressed in the direction of the wave motion. Shortens wavelength Higher frequency = higher pitch

Section 2: Characteristics of Waves Moving away Wavelength increases Smaller frequency = lower pitch Doppler Effect – observed change in frequency of a wave when the source or observer is moving.

Section 2: Characteristics of Waves

Section 3: Wave Interactions Waves tend to travel in straight lines in a medium. Three ways Waves interactions with barriers: Reflection – the bouncing back of a wave when it hits a surface that it does not go through. All types of waves can be reflected. The angle of incidence of a wave is always equal to the angle of reflection. Normal – an imaginary line perpendicular to a reflective surface Angle of incidence – the angle formed by the wave striking the surface and the normal Angle of reflection – the angle formed by the reflected wave and the normal

Light and Color Seeing Color

Section 3: Wave Interactions Refraction – the bending of a wave caused by a change in its speed as it moves from one medium to another The greater the change in speed is, the more the wave bends. When a wave passes into a material that slows it down, the wave is bent toward the normal. When a wave passes into a material that speeds it up, the wave is bent away from the normal.

Section 3: Wave Interactions Diffraction – an object causes a wave to change direction and bend around it. Reason that shadows do not have perfectly sharp edges.

Section 3: Wave Interactions Interference – the ability of two or more waves to combine and form a new wave Waves pass right through each other and continue in their original direction. New wave exists only while the two original waves continue to overlap.

Section 3: Wave Interactions Two types of Interference Constructive interference – waves add together Crest of one wave overlaps the crest of another. Destructive interference – waves subtract from each other Trough of one wave overlaps with crest of another.

Section 3: Wave Interactions Standing waves – a wave pattern that stays in one place Form when waves of equal wavelength and amplitude that are traveling in opposite directions continuously interfere with each other. Nodes – the places where two waves always cancel each other Antinodes – area of maximum vibration