Waves
Waves
A wave is a disturbance that moves through matter or space. Waves can move through solids, liquids, and gases. Waves carry energy, not matter. Waves are produced by something moving back and forth or vibrations. There are three types of waves: transverse waves, compressional waves, and electromagnetic waves.
1. Transverse Waves – a type of mechanical wave that causes the particles to move up and down at right angles to the direction at which the wave travels. High points in the waves are called crests and low points are called troughs.
2. Compressional Waves – a type of mechanical wave that causes particles to move back and forth along the same direction in which the wave travels. Where the coils are squeezed together it’s called compressions and where the coils are spread apart it’s called rarefactions.
3. Electromagnetic Waves – These are transverse waves that contain electric and magnetic parts that vibrate up and down, perpendicular to the direction of the wave (light, radio waves, x-rays)
*The properties that a wave has depends on the vibrations that produce the waves*
Parts Of A Wave
Wavelength – the distance between one point on a wave and the nearest point moving with the same speed and direction.
- Transverse - the distance between two adjacent crests
- Compressional – distance between two adjacent compressions or rarefactions.
- Frequency – the number of wavelengths that pass by a point each second
- Transverse – number of crests or troughs that go by a point each second
- Compressional – number of compressions or rarefactions that go by a point each second.
- Amplitude – (transverse) distance between the middle of the wave and the crest or the middle of the wave and the trough (compressional wave) – the amount of compressions and rarefactions
Amplitude & Energy – the vibration that produces a wave transfers energy to the wave. The more energy a wave has the greater its amplitude.
Wave Speed – Wave speed is calculated by multiplying the wavelength by the frequency. The answer is given in hertz (Hz)
Speed = Wavelength • Frequency
The above equation is known as the wave equation. It states the mathematical relationship between the speed (v) of a wave and its wavelength (λ) and frequency (f). Using the symbols v, , and f, the equation can be rewritten as
v = f • λ
Waves can change direction
Waves can change direction when they travel from one material to another. Waves can reflect (bounce off a surface), refract (change direction) or diffract (bend around an obstacle).
The Law of Reflection – a line that makes a 90 degree angle with a surface is called the normal to the surface. Using the law of reflection, the angle that the incoming wave makes with the normal equals the angle that the outgoing wave makes with the normal.
Refraction – The change of direction of a wave when it changes speed due to traveling through different materials. The speed of a wave depends on the material through which it’s traveling. A light wave travels faster through air than water. When the light wave moves from air to water it slows down. This change in speed causes the light to bend or refract. See how the straw seems to bend in the water. The straw is not bending, the light is.
Diffraction- bending the waves around an object.
Diffraction of sound and light - The wavelengths of light are much shorter than those of sound. This is why you can hear people in another room even though you can’t see them.
Sound Waves
Sound waves are compressional waves produced by vibrations. Energy travels along the wave. Sound waves can only travel through MATTER. They cannot travel through empty space because they need particles to transport energy. Therefore, there is no sound in space.
Speed of Sound
speed of sound depends upon the material that it’s traveling through. Sound waves travel fastest through solids and then liquids. The speed of sound increases as the temperature of the material increases.
Loudness of Sound
The amount of energy affects how loud or how soft sound is. Loud sounds have more energy than soft sounds. The amount of energy that a wave carries past a certain point each second is the intensity. Loudness is the human perception of the intensity of sound. The closer you are to the sound source, the more intense it will be. The more intense a wave is, the greater the amplitude of that wave.
Decibel Scale and Loudness
Sound wave intensity is measured in decibels (dB). The softest sound a person can hear has an intensity of 0 dB, normal conversation is about 50 dB and a jet plane taking off is 150 dB
Frequency and Pitch
The frequency of the sound waves is determined by the frequency of the vibrations that produce the sound. Frequency is measured in hertz (Hz). Pitch is the frequency of sound. Low and high notes produce different pitches. A tuba produces a low pitch with waves that have low frequencies. Sounds from a flute produce a high pitch with waves that have high frequencies.
Hearing and the Ear
The ear can be divided into 3 parts: 1) the outer ear, 2) the middle ear, 3) and the inner ear
You hear a sound when a sound wave reaches your ear and causes structures in your ear to vibrate.
1. The Outer Ear – is the sound collector. The visible part is shaped like a funnel to collect and direct sound waves to the ear canal.
2. The Middle Ear – This is the sound amplifier. It consists of the eardrum and 3 tiny bones called the hammer, anvil, and the stirrup. Sound waves pass through the ear canal and cause the eardrum to vibrate. The waves are then transmitted to the 3 small bones which amplify the sound.
3. The Inner Ear – is the interpreter. The sound waves move hair cells in the inner ear which then send signals to your brain to interpret these waves as sound.
The Reflection of Sound
Echoes are sounds that reflect off surfaces. Repeated echoes are called reverberation. The reflection of sound can be used to locate and identify sound. Echolocation is the process of locating objects by bouncing sound off of them. Bats use this to find their prey. They emit a short frequency sound wave towards a certain area, interpret the reflected sound waves, and locate other animals. Doctors use ultrasonic waves to produce an internal picture of the body (babies).
Light & The Electromagnetic Spectrum
Light
Light waves are transverse waves that contain vibrating electric and magnetic fields. They can travel through matter but they can also travel through empty space. Electromagnetic waves are waves that can travel through matter or through empty space.
Nothing travels faster than the speed of light. When light travels through matter, it interacts with the molecules and slows down. Light waves travel slowest in solids and fastest in space. Light from the sun reaches us in about 8 minutes. That’s extremely fast when you consider that the sun is 150 million kilometers (km) away!
Wavelengths of light are measured in nanometers (nm). 1 nm = 1 billionth of a meter (that’s a very small amount).
Properties of Light Waves
All electromagnetic waves are transverse waves. They have an electric field and a magnetic field that vibrate perpendicular to the wave. The number of times each field vibrates each second is the frequency of the wave and the wavelength is the distance between crests or troughs or vibrating electric or magnetic parts.
The intensity if a wave is the measure of the amount of energy a wave is carrying. For light waves, the intensity determines the brightness of the light. Dim light= low intensity = less energy. As you move away from the light source the energy spreads out and the intensity also decreases.
The Electromagnetic Spectrum is the complete range of electromagnetic wave frequencies and wavelengths. At the left end of the spectrum the waves have low frequency, long wavelength, low amplitude, and low energy. On the opposite side of the spectrum the waves have high frequency, short wavelength, high amplitude, and high energy. All of the waves are the same kind of wave (electromagnetic), their only difference is their frequency, amplitude, and energy.
Radio waves, microwaves, Infrared Waves, Visible Light, Ultraviolet Waves, X rays, Gamma Rays.
Radio Waves carry radio and television signals to your home and other places. Uses: listening to the radio. Microwaves are shorter than radio waves and they, not only cook food in microwave ovens, but they also transmit information to and from cell phones.
Infrared Waves – all warm bodies emit infrared waves. Night goggles are sensitive to infrared waves and can locate warm bodied animals at night. Uses: remote controllers for TV, night goggles.
Visible Light and Color – Electromagnetic wavelengths that people can see are called visible light. White light (like the light from the sun or a flashlight) is really a combination of different colors of light. A prism can separate white light into different wavelengths revealing different colors. Red light is bent the least and has the longest wavelength while violet light is bent the most and has the shortest wavelength. ROY G BIV
Ultraviolet Waves – these waves carry more energy than visible light. Sunlight that reaches Earth’s surface carry ultraviolet waves. Most of these are blocked by the Earth’s atmosphere but a small fraction gets through (hole in ozone layer). These waves can cause sunburn and permanently damage skin or cause skin cancer (melanoma). Some exposure to ultraviolet waves is needed for your body to produce vitamin D, which helps form healthy bones and teeth.
X rays and Gamma Waves – the waves have the highest energy and shortest wavelengths. X rays have enough energy to pass through soft tissue like skin but not dense materials like bones. This allows us to take internal pictures of our body parts. Gamma waves are more energetic and are used by the food industry to kill bacteria on food to keep the food from spoiling.
**Most all energy from the sun that reaches Earth’s surface is carried by infrared and visible electromagnetic waves.**
The Eye
We see objects when light emitted or reflected from an object enters our eyes. Light waves pass through a transparent (translucent, clear) layer called the cornea and then the transparent lens. The retina contains hundreds of millions of sensitive cells called rod and cone cells. Rod cells are sensitive to dim light and cone cells allow you to see color. There are three types of cone cells. (1) sensitivity to red and yellow light, (2) sensitivity to green and yellow light, (3) sensitivity to blue and violet light. The combination of signals sent to the brain by all three cone cells form that color image that you see.
Seeing Light – When light waves hit an object, the light can be either absorbed or reflected. When you see a red apple what you are really seeing is the visible light in the red wavelengths that are being reflected off of the apple. The rest of the colors were absorbed.