Waves

Waves

What are waves?

What causes waves?

• A wave is a disturbance that transfers energy from place to place.

• Waves are created when a source of energy causes a medium to vibrate.

• A vibration is a repeated back and forth or up and down motion.

Mediums

A medium is the material through which a wave travels

As a wave moves the particles of matter DO NOT move, only the energy is transferred

A medium can be a solid, liquid, or gas

Mediums cont.

The medium affects the speed of the wave traveling through it

* If you increase the temperature of the medium, the wave travels faster

* If you increase the density of the medium, the wave travels faster

Not all waves that we have require a medium

* Light from the sun travels through empty space, there is not medium there.

Mechanical waves:

Waves transfer energy without

transferring matter.

Types of waves

Longitudinal (compression)

The wave particles vibrate back and forth in the same directions that the wave travels

An example is a sound wave, slinky

Longitudinal (compression)

Wave

Parts of a longitudinal (compression) wave:

Compression: where the molecules in the wave are close together

Rarefaction: where the molecules in the wave are spread apart.

Transverse Waves

Waves that move the medium at right angels to the direction the wave is traveling. This means that the waves are moving in an up and down motion. An example would be a light wave.

Transverse Wave Vocabulary

Amplitude: height from the rest position to the crest or the trough

Wavelength: the distance between one point on the wave to the next identical point on the wave; from top to top or bottom to bottom

Crest: highest point on the wave

Trough: lowest point on the wave

Rest position: the midline of the wave, this is the line that cuts the wave in half

Transverse Wave

Properties of a wave

• Amplitude

• Wavelength

• Frequency

• Speed

Amplitude- transverse wave

The amplitude in a transverse wave is the maximum distance from the rest position to the crest or trough of the wave.

The farther the medium moves as it vibrates, the larger the amplitude of the wave. This means that the wave has a greater amount of energy.

Amplitude- longitudinal

waveThe amplitude of a longitudinal wave is measured by how compressed or rarefied the medium becomes.

Loudness measures energy in sound waves. It is measured in decibels.

Wavelength

A wave travels a certain distance before it begins to repeat. The distance between these points is called the wavelength.

In a transverse wave, it is the distance from crest to crest or trough to trough.

In a longitudinal wave, it is from one compression to the next.

Frequency

The number of waves that pass a given point in a set amount of time.

This is the number of vibrations per second.

Frequency is measured in Hertz (Hz)

Speed

The speed, frequency and wavelength of a wave are related to each other through a mathematical equation.

Speed = wavelength x frequency

Frequency = speed/wavelength

Wavelength = speed/frequency

Remember that the speed of a wave depends on the medium that it is traveling through. However, in a given medium and under the same conditions, the speed of the wave is constant.

Ways Waves Interact- Reflection

• Reflection when an object or wave hits a surface through which it cannot pass, it bounces back

Law of Reflection

Angle of incidence

Angle of reflection

Ways Waves Interact-RefractionRefraction is when a wave moves from one medium into another medium at an angle, it changes speed as it enters the second medium which causes it to bend.

Bending happens when one side of the wave enters the new medium before the other side.

Light

Light waves

• Light waves are Transverse Waves

• This means that they do not need a medium to travel. It can travel in a vacuum.

• Light waves are part of the Electromagnetic Spectrum

• Light consists of tiny packets called photons

Nature of Light

The atom is the source of all light

A photon is a tiny bundle of energy and this is what light is made of.

Light waves have different amounts of energy and most of the light waves are invisible to the human eye.

The Electromagnetic Spectrum (EMS) is both electric and magnetic.

Electromagnetic Waves

Electromagnetic waves transfer radiant energy and can travel through a vacuum.

These waves are arranged by wavelength and frequency.

Radio Waves

Radio waves have the lowest frequency

AM and FM Radio waves: AM waves bend around hills and buildings

The highest frequency radio waves are called Microwaves

used in cooking and communication

Short wavelength waves are used in radar

Infrared Waves are felt as warmth. It is sometimes referred to as a red wave.

Visible Light

Red is the lowest visible frequency and has the lowest energy of photons.

Violet is the highest frequency and has the highest energy of photons.

Ultraviolet Rays

Ultraviolet Rays are used to kill living cells.

Used in places like hospitals

Also, this ray is responsible for burning your skin

X-Rays

• Higher frequency than UV rays

• Cannot pass through dense material like bone

• Use lead to protect the body

Gamma Rays

Gamma rays are the highest energy waves. This means that they have the most amount energy

Sometimes radioactive materials can emit gamma rays

They come from outer space

Gamma rays photons can penetrate through 3 meters of concrete

Color

When light strikes any form of matter light can be:

transmitted

transparenttranslucent

absorbed

opaque

reflected

Black = absence of color

White = the presence of all colors

Primary Light Colors

These are red, blue and green

When these colors are mixed together, they form white light

Sound

What is sound?

Sound is a form of energy that causes molecules of a medium to vibrate back and forth.

Remember that all sound waves are longitudinal waves.

Waves always travel uniformly away from the source.

What affects the speed of sound?

Density- how tightly packed the molecules are:If something is more dense, the wave travels faster

Temperature: Warmer temps make the wave travel faster

Elasticity: how quickly the molecules go back together.

Wave interactions for sound

Refraction: this is when the waves bends as it enters a new medium

Reflection: when the waves hits another object and bounces off

Diffraction: when the waves bend around a barrier

Resonance: when an object vibrates at its own natural frequency

Doppler Effect

This explains why you hear things before you see them. Think about a siren on a police car, ambulance, or fire truck.

This is the change in frequency and pitch due to an objects motion.

Properties of Sound

Pitch: this is how high or low a sound is, the higher the frequency, the higher the pitch

Amplitude: this affects the intensity of the sound. This tells you how much energy is in the wave.

Quality: this refers to wave interactions.

Constructive interference: 2 waves come together and make a bigger wave

Destructive interference: 2 waves meet and they counteract each other making a smaller wave