Waves, Sound & Light-Unit 7
Medium
A medium is a substance through which a wave can travel. A medium can be a solid, a liquid, or a gas. The plural of medium is media.
Waves
Any disturbance that transmits energy through matter or empty space (A medium). Examples: water waves in the ocean; light waves from the sun; microwaves inside the microwave oven; radio waves transmitted to the radio; and sound waves from the radio, telephone, and voices.
How does constructive interference happen?
Constructive interference happens when the crests of one wave overlap the crests of another wave or waves. The troughs of the waves also overlap. When waves combine in this way, the energy carried by the waves is also able to combine. The result is a new wave that has higher crests and deeper troughs than the original waves had. In other words, the resulting wave has a larger amplitude than the original waves had.
How does destructive interference happen?
Destructive interference happens when the crests of one wave and the troughs of another wave overlap. The new wave has a smaller amplitude than the original waves had. When the waves involved in destructive interference have the same amplitude and meet each other at just the right time, the result is no wave at all.
How do electromagnetic waves differ from mechanical waves?
Electromagnetic waves transfer energy without going through a medium. Mechanical waves need a medium.
If you make three rope waves per second, what is the frequency of the wave?
Here, three waves went by in 1 s, so the frequency is 3 /1 s = 3 Hz.
How can interference and reflection cause standing waves?
If you move a rope at certain frequencies, the rope appears to vibrate in loops. The loops come from the interference between the wave you made and the reflected wave.
Longitudinal Waves
In a longitudinal wave, the particles of the medium vibrate back and forth along the path that the wave moves. You can make a longitudinal wave on a spring. When you push on the end of the spring, the coils of the spring crowd together. A part of a longitudinal wave where the particles are crowded together is called a compression. When you pull back on the end of the spring, the coils are pulled apart. Example: Sound Wave
How are Frequency and Wavelength Related?
Inversely related. If a wave is traveling a certain speed and you double its frequency, its wavelength will be cut in half. Or if you were to cut its frequency in half, the wavelength would be double what it was before. So, you can say that frequency and wavelength are inversely related.
Waves with a shorter wavelength have more or less energy? Explain
More. If you are making waves on either a spring or a rope, the rate at which you shake it will determine whether the wavelength is short or long. If you shake it rapidly back and forth, the wavelength will be shorter. If you are shaking it rapidly, you are putting more energy into it than if you were shaking it more slowly. So, a wave with a shorter wavelength carries more energy than a wave with a longer wavelength does.
Waves with a large amplitude have more or less energy? Explain
More. When using a rope to make waves, you have to work harder to create a wave with a large amplitude than to create one with a small amplitude. The reason is that it takes more energy to move the rope farther from its rest position. Therefore, a wave with a large amplitude carries more energy than a wave with a small amplitude does.
Diffraction
Most of the time, waves travel in straight lines. For example, a beam of light from a flashlight is fairly straight. But in some circumstances, waves curve or bend when they reach the edge of an object. The bending of waves around a barrier or through an opening is known as diffraction.
Energy Transfer Through a Medium: Describe
Most waves transfer energy by the vibration of particles in a medium. When a particle vibrates (moves back and forth), it can pass its energy to a particle next to it. The second particle will vibrate like the first particle does. In this way, energy is transmitted through a medium.
Describe how a particle moves in a longitudinal wave
Particles in a longitudinal wave vibrate parallel to the direction that the wave travels.
Describe how a particle moves in a transverse wave
Particles in a transverse wave vibrate perpendicularly to the direction the wave travels.
Reflection
Reflection happens when a wave bounces back after hitting a barrier. All waves-including water, sound, and light waves-can be reflected.
Refraction
Refraction is the bending of a wave as the wave passes from one medium to another at an angle.
Energy Transfer Without a Medium: Describe
Some waves can transfer energy without going through a medium. Visible light is one example. Other examples include microwaves made by microwave ovens, TV and radio signals, and X rays used by dentists and doctors.
Constructive Interference
The interference that occurs when two waves combine to make a wave with a larger amplitude.
Destructive Interference
The interference that occurs when two waves combine to make a wave with a smaller amplitude.
Types of Waves
The two main types of waves are transverse waves and longitudinal waves. Sometimes, a transverse wave and a longitudinal wave can combine to form another kind of wave called a surface wave.
Mechanical Waves
These are waves that need a medium. Examples: Sound waves, Ocean waves
Explain why waves carrying more energy have a higher frequency.
To make high-frequency waves in a rope, you must shake the rope quickly back and forth. To shake a rope quickly takes more energy than to shake it slowly. Therefore, if the amplitudes are equal, high-frequency waves carry more energy than low-frequency waves.
Transverse Waves
Waves in which the particles vibrate in an up-and-down motion. The particles in this kind of wave move across, or perpendicularly to, the direction that the wave is going. To be perpendicular means to be "at right angles." Examples: Electromagnetic Waves
Electromagnetic Waves
Waves that transfer energy WITHOUT a medium.
What do all waves have in common?
Waves transfer energy, have describable properties, and interact in predictable ways.
What happens to a wave when it moves from one medium to another at an angle?
When a wave moves from one medium to another, the wave's speed changes. When a wave enters a new medium, the wave changes wavelength as well as speed. As a result, the wave bends and travels in a new direction.
Surface Waves
When waves form at or near the boundary between two media, a transverse wave and a longitudinal wave can combine to form a surface wave. An example is ocean waves. Surface waves look like transverse waves, but the particles of the medium in a surface wave move in circles rather than up and down. The particles move forward at the crest of each wave and move backward at the trough.
Standing Waves
a pattern of vibration that simulates a wave that is standing still or a condition where two waves of equal frequency traveling in opposite directions meet and form stationary regions of maximum displacement due to constructive interference and stationary regions of zero displacement due to destructive interference
Resonance
a phenomenon that occurs when two objects naturally vibrate at the same frequency; the sound produced by one object causes the other object to vibrate
Interference
the combination of two or more waves that results in a single wave
Wavelength
the distance from any point on a wave to an identical point on the next wave
Amplitude
the maximum distance that the particles of a wave's medium vibrate from their rest position
Frequency
the number of waves produced in a given amount of time Frequency is usually expressed in hertz (Hz). For waves, one hertz equals one wave per second (1 Hz = 1/s).
Wave speed
the speed at which a wave travels through a medium Wave speed (ν) can be calculated using wavelength (λ, the Greek letter lambda) and frequency (ƒ), by using the wave equation, which is shown below: v = λ x ƒ The wave speed of a wave in a certain medium is the same no matter what the wavelength is. So, the wavelength and frequency of a wave depend on the wave speed, not the other way around.
