Objectives Recognize that waves transfer energy. Chapter 14 Objectives Recognize that waves transfer energy. Distinguish between mechanical waves and electromagnetic waves. Explain the relationship between particle vibration and wave motion. Distinguish between transverse waves and longitudinal waves.

Chapter 14 Bellringer Imagine throwing a rock into a pond or lake. Describe the effect that the rock has on the surface of the water. When surfing, a person moves just ahead of a wave. Where does the energy come from to move the surfer through the water? What happens to a string on a guitar or other stringed instrument when it is plucked? When a musician strikes two cymbals together, the cymbals will begin to vibrate and make music. How does the musician stop the music?

Energy and Waves Hz or 1/s Waves: water, sound , and light all travel in waves Wavelength: (l) the distance between peaks of a wave. (usually in meters) Frequency: (n) the number of waves that pass a given point in a specific time, usually one second. (Hertz) Hz or 1/s Waves are produced by something vibrating back and forth. Two properties of waves are wavelength and frequency. Wavelength is the distance between two corresponding points of two adjacent waves Frequency is the number of vibrations per second Low frequency results in large wavelength High frequency results in a small wavelength. OCEAN WAVES (draw on board) Electromaganetic radiation includes radio waves that carries broadcasts to your radio and TV, microwave radiation used to heat food in a microwave oven, radiant heat used to toast bread, and the most familiar form, visible light. LONG SHORT

Transverse waves: waves where particles move up and down When the wave moves through the medium, the particles are bumped perpendicular to the wave….in other words….away from the wave.

Longitudinal Waves: the particles vibrate back and forth (they are not bumped up and down). Pushing a spring back and forth creates a longitudinal wave

So what is the difference?...... A) is a Longitudinal wave – back and forth- vibrations – aka… oscillations. B) is a transverse wave – up and down

http://physics-animations.com/Physics/English/top10.htm

What do waves do? 1) Waves carry energy away from its source. 2) Waves carry energy, but not matter 3) As a wave travels, it uses energy to do work on everything in its path 4) Waves are energy traveling through matter and acting on that matter (making it move or heat up) 5) The matter that it travels through can move two different ways depending on the type of wave. The object can move up and down- like a leaf floating and moving as the waves of a pond move toward the shore The object can move in circles- like ocean waves where water meets air

Chapter 14 Section 1 Types of Waves Water Wave Motion

Chapter 14 Objectives Identify the crest, trough, amplitude, and wavelength of a wave. Define the terms frequency and period. Solve problems involving wave speed, frequency, and wavelength. Describe the Doppler effect.

Chapter 14 Bellringer There are many different types of waves. You may be familiar with the electromagnetic spectrum, which includes radio waves, microwaves, infrared light, visible light, ultraviolet light, X rays, and gamma rays. Name five common applications of waves in the electromagnetic spectrum, and list the type of wave used in each case. Lasers are made from accurately focused visible light waves that are produced in phase with each other. Lasers made from visible light waves are often used in surgery to perform delicate procedures and to seal the area being treated.

Part of a wave Crest: High point of a transverse wave Trough: lowest point of a transverse wave

Compression: crowded area of longitudinal waves Rarefaction: the expanded part of the longitudinal wave

Amplitude: the height of the peak – measured from the rest position It takes more energy to move far from rest position Wavelength : distance between ….. Two adjacent Peaks of transverse waves Two adjacent compressions of longitudinal wave Rest position

Amplitude Greater Amplitude Smaller Amplitude Higher Energy Louder Sound Smaller Amplitude Lower Energy Softer Sound

Waves Wave: a wave is produced by a vibrating object. Mechanical Waves: a wave that passes through matter, and causes the matter to vibrate, but the energy of the wave passes through. (resonance) Requires a medium (substance like solid, liquid, gas) Like sound waves or ocean waves If there are no particles to vibrate, then nothing happens, no motion, no sound…..nothing! Electromagnetic wave: waves that transfer energy without travelling through a matter) Does not require a medium Like x-rays, and ultraviolet, infrared, and radio waves

C = ln E = hn Speed of a wave (C): The speed of a wave depends on the medium it is traveling through Speed of light: 3 x 108 m/s (traveling through air) Speed of sound: 340 m/s (traveling through air) C = ln Wavelength and Frequency are opposites. (they are indirectly related) One goes up to other goes down. E = hn Energy and Frequency are the same. (they are directly related) One goes up the other also goes up. The properties of wavelength and frequency are similar to that of ocean waves. Frequency and wavelength are mathematically related to one another. The wave theory of light has been very important in science but in the 1900s, scientists conducted two experiments involving light and matter that could not be explained by waver theory of light. The first experiment was the photoelectric effect. For a given metal, no electrons were emitted if the light’s frequency was below a certain minimum-regardless of how long the light was shone. The wave theory of light predicts that light at any frequency could supply enough energy to eject an electron. But it didn’t work at low frequencies. The photoelectric effect is like a soft-drink machine that works only when a single coin of sufficient value is inserted. If a combination of smaller coins is inserted, nothing happens, even though the combination adds up to the value of the single coin. An electron remains bound to a metal unless a single photon with the required minimum energy hits the electron. Max Plank proposed that a hot object does not emit electromagnetic energy continuously (as would be expected is the energy emitted were in the forms of waves) Instead Plank suggested that object emit energy in small, specific amount called Quanta.

Chapter 14 Frequency

How Light Works Photon: a particle of electromagnetic radiation that has energy and no mass. (tiny packets of energy) Different wavelengths of light carry different amounts of energy The energy in a photon depends on the amount of energy released when an atom goes from an excited state to a ground state In 1905 Albert Einstein expanded on plank’s theory by introducing that electromagnetic radiation had a dual wave -particle nature. Light can be thought of as a stream of particles. Each particle carries a quantum of energy. Einstein called these particles photons. Einstein proposed that electromagnetic radiation is absorbed by matter only in whole number of photons. Since a metal must be struck by a single photon possessing at least the minimum energy required to knock an electron loose. Electrons in different metals are bound more or less tightly , so different metals require different minimum frequencies to exhibit the photoelectric effect.

Emission Spectrum The emission spectrum of each element is unique Ground State: the lowest energy state of an atom Excited State: the high energy state of an atom when excited atoms return to their ground state, they emit energy/photon of radiation. ( example: Neon signs) Line-emission spectrum: bands of light resulting from a narrow beam of light shined through a prism. The emission spectrum of each element is unique

Line and absorption spectra

Electromagnetic Radiation: energy that exhibits wave like behavior as it travels through space. moves at the speed of light Electromagnetic radiation is usually called light. It is divided into various classes Gamma rays, X-rays, ultraviolet and infrared light, microwaves, and radio waves form the electromagnetic spectrum

The Electromagnetic Spectrum Chapter 14 The Electromagnetic Spectrum

Gamma-rays: radioactive materials X-rays: pass through soft body tissue but are stopped by harder tissue, like bone Ultraviolet: part of sunlight that causes sunburn and cancer. The ozone absorbs most of the sun’s UV rays Stars and other "hot" objects in space emit UV radiation Visible light: part of the spectrum to which our eyes are sensitive our eyes and brain interpret different frequencies as different colors ROYGBIV What are the colors of visible light? ROYGBIV If I asked what colors went into something that was white in color, what would you say? (white is the presence of all color) White light is a mixture of all color of visible light IF UV visible light is all colors why can’t we see it all the time? Why can we only see a rainbow when the white light passes through a rain drop? How come we can’t see a rainbow when we see light? How can we? Through a prism! The prism separate the individual waves Now we can take the radiation from gases and put it through a prism to reveal that gases spectrum.

Microwaves: used for communications and cooking Infrared: radiation given off by the human body and most other warm objects. (fire, heaters) Microwaves: used for communications and cooking Radio: lowest frequencies of the spectrum When current is passed through a gas at low pressures, the potential energy os some of the gas atoms increase. At the ground state, an atom has it’s lowest possible energy. An excited neon atom emits light when falling back to the ground state or to a lower energy state. When an excited atom returns to its ground state, it gives off energy, in the form of electromagnetic radiation. When you pass an electric current through hydrogen gas, a pinkish glow is given off. When a narrow beam of light is shined through a prism, it is separated into a series of specific frequencies of visible light. The bands of light are part of what is known as hydrogen’s line-emission spectrum. (excited hydrogen emits a pink glow, when the visible portion of the emitted light is passed through a prism, it is separated into specific wavelengths) Classical theory predicted that the hydrogen atom would be excited by whatever amount of energy was added to them. They expected to observe the emission of continuous range of frequencies of electromagnetic radiation. So, why did the hydrogen atoms give off only specific frequencies of lights When an excited atom falls back from an excited state to it ground state or to a lower energy state, it gives off energy. Because hydrogen only emits a specific set of frequencies of light, hydrogen’s energy states must be fixed. This suggests that the electron of a hydrogen atom exists only in very specific energy states.

Chapter 14 Bellringer The back of a mirror is flat and highly reflective. Describe how you think a mirror works. Why do you think one piece of safety equipment that backpackers carry into the wilderness is a mirror? Describe what an echo is. Blinds in the windows of homes, schools, and offices can be tilted up or down, or they can be closed completely. Explain how varying positions of the blinds controls light.

What can we do to waves? Reflect them: when a wave bounces back after hitting something Refract them: when a wave is bent or broken down because it starts travelling in a new medium light through a prism Because the speed of a wave depends on the medium it is in, when the wave enters a new medium, it starts to travel at a different speed, thus is bends) Diffract them: waves that travel around a barrier or through an opening Like sound that travels around a corner so that you can hear it.

Reflection, Diffraction, and Refraction Chapter 14 Reflection, Diffraction, and Refraction Reflection is the bouncing back of a ray of light, sound, or heat when the ray hits a surface that it does not go through. Waves reflect at a free boundary. The reflected wave is exactly like the original wave except that the reflected wave is traveling in the opposite direction to the direction of the original wave. At a fixed boundary, waves reflect and turn upside down.

Reflection

and reflection in mirrors Refraction in lenses and reflection in mirrors

Chapter 14 Reflection

Reflection, Diffraction, and Refraction Mirrors Flat form virtual images…brain interprets light so images appear as far behind the mirror as the object s in front of it Curved distort images Concave form real images…light rays actually focused Convex…side view mirror, traffic mirrors

Reflection, Diffraction, and Refraction Refraction: light waves bend or refract when they pass from one medium to another Makes objects appear to be in different positions Creates mirages Fiber optics Lenses…microscopes, telescopes, glasses, eyes! Prisms Rainbows (reflection and refraction)

Lawnmower analogy for refraction

Refraction

Refraction and reflection

and reflection in mirrors Refraction in lenses and reflection in mirrors

Diffraction Diffraction…wave encounters an obstacle or a slit. Involves interference.

Constructive and Destructive Interference

Constructive interference increases amplitude. Constructive interference is any interference in which waves combine so that the resulting wave is bigger than the original waves. The amplitude of the resulting wave is the sum of the amplitudes of the two individual waves. Destructive interference decreases amplitude. Destructive interference is any interference in which waves combine so that the resulting wave is smaller than the largest of the original waves. When destructive interference occurs between two waves that have the same amplitude, the waves may completely cancel each other out.

Interference, continued Chapter 14 Interference, continued Interference of light waves creates colorful displays. Interference of sound waves produces beats. When two waves of slightly different frequencies interfere with each other, they produce beats.

Standing Waves Interference can cause standing waves. A standing wave is a pattern of vibration that simulates a wave that is standing still. Standing waves can form when a wave is reflected at the boundary of a medium. Although it appears as if the wave is standing still, in reality waves are traveling in both directions.

Standing waves have nodes and antinodes. Each loop of a standing wave is separated from the next loop by points that have no vibration, called nodes. Nodes lie at the points where the crests of the original waves meet the troughs of the reflected waves, causing complete destructive interference. Midway between the nodes lie points of maximum vibration, called antinodes. Antinodes form where the crests of the original waves line up with the crests of the reflected waves, causing complete constructive interference.

Standing waves can have only certain wavelengths. Chapter 14 Standing waves can have only certain wavelengths. In general, standing waves can exist whenever a multiple of half-wavelengths will fit exactly in the length of the string. It is possible for standing waves of more than one wavelength to exist on a string at the same time.

Doppler Effect Pitch is determined by the frequency of sound waves. The pitch of a sound, how high or low it is, is determined by the frequency at which sound waves strike the eardrum in your ear. A higher-pitched sound is caused by sound waves of higher frequency. Frequency changes when the source of waves is moving. The Doppler effect is an observed change in the frequency of a wave when the source or observer is moving.