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Transcript

Unit 1: Waves

Sound

Sound

Properties

Sound as a Longitudinal Wave

When an object vibrates, it is producing a sound. First, the molecules directly next to the object vibrate. They bump into the next molecules to make them vibrate, which bump into the next molecules, and so on.

Because the particles are moving in the direction of the sound itself, it is known as a longitudinal wave. Longitudinal waves move particles from side to side, along the wave itself. P waves are an example. Waves that move particles up and down are known as transverse. Light waves are an example (sound is not!)

Longitudinal waves can move through any medium (solid, liquid, or gas). But, they cannot move through a vacuum, like space, because there are no molecules for the sound to bump into. Because they require a medium to move forward, sound waves are known as mechanical waves.

Amplitude

Amplitude is the LOUDNESS of a sound. When a sound is produced, each individual molecule of the medium moves back and forth. If a sound is loud, it has a high amplitude, and the molecule will go a far distance before returning to its original position. If a sound is quiet, it has a low amplitude, and it will travel a short distance before returning to its original position. You can think of loud sounds as giving the molecules more energy to travel further.

Frequency

Frequency is the amount of times an air molecule moves back and forth in a second, and is measured in hertz. A sound has a high frequency if it causes an air molecule to vibrate back and forth a lot of times in a second. It has a low frequency if it causes an air molecule to vibrate back and forth only a little bit.

It is important to note that how many times a molecule vibrates is NOT the same thing as how far the molcule moves during a vibration. So....FREQUENCY HAS NOTHING TO DO WITH LOUDNESS!! The ONLY thing that determines loudness is amplitude.

Pitch

Pitch is whether a sound is heard as high or low.

High frequency = high pictch

Low frequency = low pitch

Simple as that!!!

Compressions, Rarefactions & Wavelength

Remember sound is a longitudinal wave, where molecules in a horizontal line bump into each other. This naturally creates two phenomena:

  • Compression: areas where the molecules are closer together than normal, with high density & pressure
  • Rarefaction: areas where the molecules are more spread out than normal, with low density & pressure

When a molecule moves back and forth one time, it has completed one wavelength. In other words, one wavelength includes one compression and one rarefaction. In other other words, a wavelength can be defined as the distance between two compressions.

Sound & Hearing

The Ear (and hearing)

The 3 parts of the ear

3 Parts of the Ear

Outer ear: consists of the earlobe and ear canal

Middle ear: consists of the ear drum and 3 tiny bones called:

  • Hammer
  • Anvil
  • Stirrup

Inner ear: consists of the cochlea lined by hair cells

The Journey of Sound (Pathway)

The Journey of Sound

1) The outer ear directs sound waves into the ear, through the ear canal

2) The eardrum vibrates from these incoming sound waves. Each sound wave is different, and creates a unique vibration! These vibrations are recorded by the hammer, anvil, and stirrup and sent to the cochlea

3) The cochlea turns the vibrations into an electrical impulse (hair cells detect different pitches!) This electrical impulse is sent through the auditory nerve to the brain. Your brain then interprets the sound!

To summarize:

Outer Ear > Sound Wave > Middle ear (hammer, anvil, stirrup) > Vibrations > Cochlea > Electrical Impulse > Brain

All about light

Light

The EM Spectrum

The Electromagnetic Spectrum

EM waves are different from the waves we've studied so far because they are not mechanical (they can travel through a vacuum). EM waves are also transverse because the wave moves perpendicular to the electric and magnetic fields

The key to understanding the electromagnetic spectrum is knowing that the WAVELENGTH of an EM wave determines what it is. All of the waves that make up the electromagnetic spectrum have a different wavelength, which determines their properties

Electromagnetic Spectrum Continued

The different categories of EM waves are: gamma rays, X-rays, UV rays, visible light, infrared waves, microwaves and radio waves. Again, the major distinction between each type of wave is the wavelength

As you move to the left, the wavelength gets smaller and the energy increases. Gamma rays have the most energy and the shortest wavelength. As your move to the right, the wavelength gets larger and the energy decreases. Radio waves have the largest wavelength and the least energy.

Visible Light

Visible Light includes the range of wavelengths that our eyes can perceive.

The range of visible light goes from ~380 nanometers (violet)- ~740 nanometers (red). Anything below 380 nm or above 740 nm counts as EM radiation but cannot be perceived by the human eye

The visible light spectrum is usually referred to as ROYGBIV (red, orange, yellow, green, blue, indigo, violet)

On the visible light spectrum, violet has the smallest wavelength and the highest energy, while has the largest wavelength and lowest energy

How Light Moves

How Light Travels

Light moving in a vacuum travels at the constant speed of 300,000,000 m/s

Light can travel through a medium (solid, liquid, or gas) as well! It does so in several ways:

- Transmission

- Reflection

-Absorption

-Refraction

Transmission

In transmission light moves straight through a material/object. In other words, light moves through a material without being reflected, absorbed, or refracted

Absorption

Absorption happens when a material "captures" light/ EM radiation. It then takes the captured light and converts it into energy, usually in the form of heat. Black absorbs all colors of light

Reflection

Reflection happens when light/EM Radiation bounces off a surface. The incoming light is known as incident light. When light hits a smooth surface, the angle of incidence is equal to the angle of reflection

Humans see the color that is reflected from an object. For example, a leaf reflects green light; a banana reflects yellow light. White reflects all colors

Refraction

Not to be confused with a rarefaction, refraction happens when light bends. Refraction only happens when light changes medium (for example, moving from a solid into a liquid, or from a gas into a liquid).

Refraction happens because light moves at different speeds in different mediums. For example, light moves faster in a gas than in a solid. So when light enters the ocean from the air, it slows down. This causes the light to "bend," or enter the water at an angle

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