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S8P4. Waves
What is a wave and how does light and sound transfer energy from one place to another?
Page 115
A wave is a rhythmic disturbance that transfers energy through matter or space WITHOUT transferring matter.
Waves can be categorized by whether or not they require a medium. A medium is matter that waves sometimes travel through. A medium can be a solid, liquid or gas. Water is the medium for ocean waves and air is the medium for sound waves.
A mechanical wave is a wave that requires matter. Examples – ocean waves, sound waves, and seismic waves
An electromagnetic wave is a wave that does not require a medium even though it can have one. Examples- radio waves, microwaves, and visible light.
On page 114 – Classify each of the following examples of waves as either mechanical waves or electromagnetic waves in a 2-column table.
Ocean, light, radio, television, seismic, sound, microwaves, gamma radiation, ultraviolet, tidal waves
Mechanical Electromagnetic
Page 117
Waves can also be categorized by how they move. A wave that transfers energy in a direction perpendicular (at a right angle) to its medium is called a transverse wave.
A transverse wave is made of high points called crests and low points called troughs. Ex. – ocean waves
A wave in which the particles vibrate back and forth (parallel) along the path that the wave moves is known as a compressional wave or longitudinal wave.
Compressional waves are made up of areas where the particles are crowded together called compressions and areas where the particles are spread out called rarefactions.
Top half of page 116 – Transverse wave illustration with properties
Bottom half of page 116 – Compressional (longitudinal) wave illustration with properties
Page 119
A wave in which the particles vibrate back and forth along the path that the wave moves is known as a compressional wave or longitudinal wave.
Compressional waves are made up of areas where the particles are crowded together called compressions and areas where the particles are spread out called rarefactions.
Compressional waves move parallel to the direction the particles are moving.
Top half of page 120 –
Bottom half of page 120 –
Wavelength – the distance between two adjacent crests or two adjacent troughs of a transverse wave.
Frequency – the number of wavelengths that pass a given point in one second; it is measured in a unit called Hertz.
Wavelength and frequency are directly related. The longer the wavelength, the lower the frequency. The shorter the wavelength, the higher the frequency.
A high frequency wave has high energy. A low frequency wave has low energy.
On page 122 – copy Figure 6 and the caption located on page 494 of the textbook.
Pages 122 - 123The electromagnetic spectrum is the range of all possible electromagnetic waves (radiation) with different frequencies and wavelengths. Electromagnetic waves can travel through matter or space.
Pages 122 - 123The electromagnetic spectrum is the range of all possible electromagnetic waves (radiation) with different frequencies and wavelengths. Electromagnetic waves can travel through matter or space.
Ex. radio, television, cell phones
Ex. microwaves, radar
Ex. remote controls, some snakes
ROYG
BIV
Ex. sunlight
Ex. bone images
Ex. nuclear reactions
S8P4b. & S8P4d. Wave Behavior
Why is it difficult to grab items from the bottom of a swimming pool? Why do straws in glasses appear broken?
Page 125
Waves can change direction when they encounter matter. They can reflect, refract and/or diffract. Waves can also interfere with one another.
Reflection - A wave is reflected when it strikes (hits) matter and bounces off of the matter. The smoother the surface that it hits, the clearer the reflected wave. The rougher the surface, the more distorted the image. An image in a mirror is a reflected light wave. An echo is a reflected sound wave.
According to the law of reflection for a smooth surface, the angle of incidence is equal to the angle of reflection.
On page 124 - Reflection
Using the image, what do you think these terms mean? - Incident ray - - Reflected ray - - Angle of incidence - - Angle of reflection -
On page 124 - Reflection
Using the image, what do you think these terms mean? - Incident ray – the wave source (the beam of light from the flashlight) - Reflected ray – the reflected wave (the light that bounces off the surface) - Angle of incidence - the angle the incident wave strikes the surface - Angle of reflection - the angle the reflected wave bounces off the surface
Page 127
Refraction – A wave is refracted when it bends as it passes from one medium to another (one type of matter to another). When a wave goes from one medium to another, it either speeds up or slows down depending on the material. An example of refraction is when a straw appears broken when in a glass of water. Another example is when it is difficult to pick up items from the bottom of a pool.
When white light is refracted it can be separated into its component colors (ROYGBIV).
Diffraction – A wave is diffracted when it bends and/or spreads as it passes through an opening or around an object.
On top of page 126 – Refraction
On bottom of page 126 –Diffraction
Page 129
Interference – is the combination of two or more waves that results in a single wave. When waves combine by interference, the amplitude of the resulting wave is different from the amplitude of the original waves.
When the crests of two waves overlap with each other, the resulting wave has a greater amplitude than the amplitude of the original waves. This is called constructive interference.
When the crest of one wave overlaps with the trough of another wave, the resulting wave has a smaller amplitude than the original waves. This is called destructive interference.
A
B
original waves resulting wave
original waves resulting wave
Label A and B as either constructive interference or destructive interference.
page 128
S8P4. Wave Behavior
What happens when a substance absorbs light?
Page 131
Light waves interact with matter by transmission and absorption. All objects reflect and absorb some light waves. When light waves strike an object, some of the waves are absorbed by the object, some are reflected by it, and some might pass through it.
Materials that let no light pass through are opaque. You cannot see other objects through opaque objects.
Materials that allow nearly all the light that strikes them to pass through are called transparent.
Materials that allow only some light to pass through are translucent. Objects behind translucent materials are only barely visible.
Categorize each of the following materials as either transparent, translucent or opaque in a 3-column table.
Book Clear window Scissors Waxed paperWhiteboard Stained glass window Camera Camera lensPencil Saran Wrap Aluminum Foil Frosted glass magnifying glass lens glasses lenses bricks clear light bulbSpeaker eraser sweet tea drinking water
page 130
Transparent Translucent Opaque
Page 133
The color of an object depends on the light waves it reflects. An apple appears red because only red light is reflected back to your eye and the other colors are absorbed by the object.
The primary colors of light are red, green and blue. When these colors of light (all colors of the spectrum) are combined, white light is produced.
The primary colors of pigment are yellow, cyan and magenta. When these colors of pigment (all colors) are mixed together, it forms black.
Summary
S8P4. Sound
What makes a sound wave move faster in hot or humid weather?
Page 135
A sound wave is a mechanical wave produced by a vibrating object. Sound waves cannot travel through empty space or a vacuum. They need matter.
When the object vibrates, it causes the molecules around it to compress (compression) and expand (rarefaction) until it reaches your ear.
Sound travels faster through solids than through liquids and gases. Also, as the temperature increases, the speed of sound increases and when the air is more humid, the speed of sound increases.
Summary
S8P4. Sound
What makes a sound softer or louder? What is the difference between a soprano voice (high) and a bass voice (deep)?
Page 137
The amplitude is the wave’s intensity (the amount of energy the wave is carrying). The higher the amplitude, the more energy being carried and the louder the sound.
The intensity or volume of a sound is measured in units called decibels. The higher amplitudes are louder and have a higher number of decibels. Lower amplitudes are softer and have a lower number of decibels.
The frequency of a wave affects the pitch. The higher the frequency, the higher the pitch (Ms. Price’s voice). The lower the frequency, the lower the pitch (Mr. Ennis’ voice).Summary
page 136
