Chapter 20 - Waves. A wave - Eg: A musician s instrument; a cell phone call & a stone thrown into a pond A wave carries from one place to another.

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1 Section Waves Chapter 20 - Waves A wave - Eg: A musician s instrument; a cell phone call & a stone thrown into a pond A wave carries from one place to another. Waves can change motion, we know that waves are a traveling form of. Waves carry information: conversations, pictures, or music. your car stereo, television. All the information you receive in your eyes and ears comes from waves The light from the traffic light is a wave. The ripples in the puddle of water are waves. The electricity flowing in the wires attached to the street lights is a wave. Waves carry radio, TV, and cell phone transmissions through the air all around you. Recognizing waves AGAIN: All waves are traveling oscillations that move energy from one place to another. Waves are present: when you see a vibration that moves. Example: A after it is plucked when something makes or responds to sound. Example: A or your ears when something makes or responds to light. Example: A or your eyes when technology allows us to see through objects. Examples: ultrasound, CAT scans, MRI scans, and X rays when information travels through the air (or space) without wires. Example: A for receiving television signals Your remote control to your TV uses light that is invisible to the eye which is a wave. Properties of Waves The properties of waves are the same as they were for oscillations/vibrations which were:,, and amplitude. Waves also have two new properties, which are: and. Wave Travel For a wave to travel, need to be or in contact with each other. Because air molecules collide, can travel in the air. A wave can travel along a string because molecules are connected. However, if you cut the string, a wave would not spread across the break.

2 Wave Types (2) 1. Transverse waves A transverse wave has its oscillations/vibrations to the direction the wave moves. DEMO TIME 2. Longitudinal waves A longitudinal wave has oscillations/vibrations in the as the wave moves. DEMO TIME AGAIN. Sound waves are longitudinal waves - like a wave pulse on a spring, air molecules oscillate back and forth as sound travels. Frequency, Amplitude, and Wavelength Frequency The frequency of a wave is a measure of how often it goes &. The frequency of the motion of one point on the wave is equal to the frequency of the whole wave. Frequency is measured in (Hz) A frequency of 1 Hz causes everything it touches to oscillate at 1 per. Amplitude The amplitude of a wave is the the wave causes anything to move away from. It = one-half the distance between the highest and lowest points. Wavelength A wave as a series of & points. A is a high point of the wave. A is the low point. is the distance from any point on a wave to the same point on the next cycle of the wave. One wavelength [lambda (λ)] is the length of one complete cycle of the wave.

3 Wave Speed What is moving? The speed of a wave is different from the speed of a moving object, like a ball. The speed of a ball is the speed at which the ball itself moves. The speed of a wave is the speed at which the wave s oscillations travel through a material. When a wave moves through water, the water itself.. Water wave speed - few miles per hour. Light waves - m/s. Sound waves travel at about miles per hour (about 1,000 km/h), faster than water waves and much slower than light waves. What is the speed of a wave? The speed of the wave is how fast the wave* gets from one place to the next, NOT how fast the wave surface moves up and down. Remember: Up-Down speed of the water surface determines its frequency. Calculating Wave Speed Speed of a wave = frequency x wavelength. Formula: V = (f) (λ) m/s = (Hz) (m) Recall: The units of Hz are 1 second. Problems: 1. The wavelength for a wave is 0.5 meter, and its frequency is 40 hertz. What is the speed of this wave? 2. The frequency of a wave is 50 hertz and the wavelength is meter. What is the wave speed? 3. The period of a wave is 10 seconds and the wavelength is 2 meters. What is the wave speed?

4 Standing Waves A wave that is is called a standing wave. Standing waves can be almost any kind:,, and even light. You can experiment with standing waves using a. Harmonics A string with a standing wave is a kind of oscillator. Like all oscillators, a string has natural frequencies. The lowest natural frequency is called the. A vibrating string also has other natural frequencies called. Determine the number harmonics by counting the number of bumps. The bump on a wave is called the. Points where the string is not moving are called. Wavelength & Frequency Relationship As frequency increases, wavelength decreases (shorter λ). As frequency decreases, wavelength increases. They are to one another. One complete S shape on the string is one wavelength.

5 Section 20.2 Wave patterns and directions The observation of water waves is utilized because they are slow and easy to see. Waves, which means they spread out from where they begin. When you drop a ball into water, some of the water is pushed aside and raised by the ball. The wave spreads through the interaction of each bit of water. Plane waves and circular waves The crests of a form a pattern of parallel straight lines called. The crests of a form a pattern of circular wave fronts. A plane wave is started by disturbing water in a line. A circular wave is started by disturbing water at a single point. The direction a wave moves depends on the of the wave front. Plane waves are straight and move in a line perpendicular to the crest of the wave. Circular waves move outward in a circle from the center. Boundaries Waves are affected by where conditions or materials change. A boundary is an or where things change suddenly. The surface of glass is a boundary. A wave traveling in the air sees a sudden change to a new material (glass) as it crosses the boundary. Several things can happen at a boundary.,, and usually occur at boundaries, as well as also occurs at a boundary.

6 The four wave interactions with objects When a wave hits an object or a surface, 4 things can happen: Reflection - is when a wave. A reflected wave is like the original wave but moving in a new direction. ** The and are usually not changed. Ex: an wave reflecting from a distant object or wall. ( ) Refraction - occurs when a wave as it a boundary. ** The and are usually changed. Ex: bend incoming light waves so that an image is correctly focused within the eye. Diffraction - process of bending around or passing through A wave is diffracted when it is by passing through a hole or around an edge. Diffraction usually changes the and of the wave. When a plane wave passes through a narrow opening diffraction turns it into a circular wave. Ex: Hearing through a crack in the door.. Absorption is what happens when the of a wave gets smaller and smaller as it passes through a material. The is transferred to the absorbing material. Theaters Curtains absorb energy. Tinted glasses absorb energy.

7 Section 20.3 Wave Interference and Energy You almost never see (or hear) a single wave with only. You really see (or hear) a complex of many different frequencies and amplitudes, all mixed together. In reality, single waves are quite rare. happens when two or more waves mix together. Interference mixes waves in ways that are very useful but can also be dangerous. Ex: radio and television use the interference of two waves to carry &. Or: sometimes water waves add up to make a gigantic wave that may last only a few moments, but can sink even the largest ship called a wave. The superposition principle - Many waves can be in the same system at the same time. - states that the total vibration at any point is the from each individual wave. The and waves you experience are the superposition of thousands of waves with different and. Your eyes, ears, and brain separate the waves in order to recognize individual sounds and colors.

8 Constructive and Destructive Interference Constructive interference When the waves meet, they combine to make a single large pulse, this is and occurs when waves add up to make a. Constructive interference is useful in working with light and sound. For example, when two sound waves constructively interfere, loudness increases. Destructive interference There is another way to add two pulses. When the pulses meet in the middle, they each other out. One pulse pulls the string up and the other pulls it down. The string flattens and both pulses vanish for a moment. In, waves add up to make a wave with smaller or zero amplitude. After interfering both wave pulses separate again and travel on their own. Waves still store, even when they interfere. Noise cancelling headphones are based on technology that uses destructive interference. Natural frequency and resonance Waves can have natural & just like oscillators. But first, a wave has to be caught in a system with boundaries. Light keeps going in a. There is no resonance. But catch the light between two perfect mirrors and you can get, which is exactly how a laser works! Resonance and reflections Resonance in waves comes from the interference of a wave with its own. One end of the string is tied to the wall, making a boundary. A pulse launched on the reflects off the wall and comes back on the of the string. Resonance and constructive interference To build up a large wave, you wait until a has returned to your hand before launching a new pulse. Resonance is created by adding new pulses so that each adds to the reflected pulse in. A single large wave motion, and you have resonance. Why resonance is important The of the oceans, musical instruments, the, the way our ears separate sound, and even a microwave oven are all examples of waves and resonance.

9 Waves and Energy A wave is a form of moving energy When you drop a stone into a pool, most of the stone s is converted into water waves. The waves spread out carrying the far from the place where the stone fell. Frequency and energy The energy of a wave is proportional to its frequency. Higher frequency means energy. This is obvious for a jump rope. You have to move the rope up and down twice, doing twice as much, to make the rope swing at twice the frequency. The wave with the higher frequency has more. The result is true for almost all waves. The energy of a wave is proportional to its frequency. Amplitude and energy The energy of a wave is also proportional to amplitude. Given two standing waves of the same frequency, the wave with the larger amplitude has more energy. With a vibrating string, the of the wave comes from the stretching of the string. Larger amplitude means the string has to stretch more and therefore stores more energy. Why are standing waves useful? Standing waves are used to at specific frequencies. With the wave on the string you observed how a of energy at the natural frequency accumulated over time to build a wave with much more energy. Musical instruments use standing waves to create sound energy of exactly the right frequency. and also use standing waves to create power at specific.