Sound and Light

Chapter 1: Characteristics of Waves

Section 1: What are Waves3: 38.08/58 = 60.48%

5: 46.05/58 = 79.40%

6: 45.80/58 = 78.97%

Vocabulary

Wave Energy Medium Mechanical Wave Vibration Transverse wave

Crest Trough Longitudinal wave Compression Rarefaction

Waves and Energy A wave is a disturbance that transfers energy from

place to place. Remember, energy is the ability to do work. Think about a raft on the water

Wave disturbs surface as well as raft. But the disturbance caused by the wave is temporary, and the wave passes, and raft returns to normal.

Most kinds of waves require something to travel though. The material through which a wave travels is called a

medium. Waves that require a medium are called mechanical

waves. Waves that don’t require a medium are called

electromagnetic waves

How do waves transfer energy?

Although mechanical waves travel though a medium, they don’t carry the medium with them.

The wave just makes the medium move back and forth, it is the energy that is getting transferred. Think of the “wave” at a sporting event

What causes waves?

Energy is always required to make a wave. Mechanical waves are produced when a

source of energy causes a medium to vibrate. A vibration is the repeated back and forth or up

and down motion. When a vibration moves through a medium, a

wave results. Remember, anything that moves has energy,

so a moving object can give its energy to a medium, and make a wave.

Types of Waves Transverse Waves

Waves that move the medium at right angles to the direction the wave travels.

As a transverse wave moves, the particles of the wave move at right angles to the direction of the wave.

Longitudinal Waves These waves move the medium parallel to the

direction in which the wave travels. Compression is where the medium is close

together Rarefactions are where the medium is far

apart.

We can use diagrams to represent transverse and longitudinal waves.

Sound and Light

Chapter 1: Characteristics of Waves

Section 2: Properties of Waves

Vocabulary

Amplitude Wavelength Frequency

Amplitude Remember, all mechanical waves move medium. The distance the medium moves depends upon the

amplitude. Amplitude is the maximum distance that the

particles of the medium carrying the wave move away from their rest positions.

More energy = Greater Amplitude For transverse waves: Amplitude is the maximum distance

up or down the wave moves. Higher/lower waves = greater amplitude

For longitudinal waves: Amplitude is the measure of how compressed or rarefied the medium becomes. Dense compressions = greater amplitude

Wavelength

Wavelength A wave travels a certain distance before it starts

to repeat. The distance between two corresponding parts of

a wave is the wavelength. Transverse Wave: Wavelength can be found by

measuring distance from crest to crest or from trough to trough.

Longitudinal Wave: Wavelength can be found by measuring distance between compressions.

Frequency

Wave frequency is the number of complete waves that pass any given point in a certain amount of time. If I make waves in a rope so that one wave

passes a given point every second, the frequency of the wave is 1 wave per second.

Frequency is measured in unit of hertz (Hz) The wave above would have a frequency of 1 Hz.

Speed of Waves

Different waves travel at different speeds. The speed of a wave is how far the wave

travels in a given length of time Or the distance divided by the time it took to travel

that distance.

Relating Ideas

Speed, wavelength and frequency are mathematically related.

Speed = Wavelength x Frequency Wavelength = Speed / Frequency Frequency = Speed / Wavelength

Sound and Light

Chapter 1: Characteristics of Waves

Section 3: Interactions of Waves

Vocabulary Reflection Refraction Law of reflection Diffraction Interference Constructive Interference Destructive Interference Standing wave Node Antinode Resonance

Reflection

When a wave hits a surface though which it cannot pass, it bounces back. This interaction is called

reflection All waves obey this.

The law of reflection states that the angle of incidence equals the angle of reflection.

Refraction When a wave moves

from one material to another, it encounters a change in wave speed.

If the wave is at an angle, one side change speed before the other, causing it to bend.

This bending of waves due to a change in speed is called refraction. Again, the wave MUST

enter an angle for this to occur

White light and refraction

White light is made of lots of different frequencies of light

When white light refracts, each color bends by different amounts. This separates the colors Rainbows!

Diffraction

When a wave moves around a barrier or after it passes through a narrow channel it will bend and spread out. This is called diffraction.

Like refraction, it involves the bending of waves.

Unlike refraction, does not pass through any new materials.

Interference Interference is an interaction that occurs whenever two

waves meet. Two types of interferences

Constructive Interference Occurs when two waves combine to make a wave with a bigger

amplitude Occurs when crests of one wave overlap with crests of another

wave (or troughs and troughs) Destructive Interference

Occurs when two waves combine to make a wave with a smaller amplitude

Occurs when crests of one wave overlap the troughs of a 2nd wave. If crest is larger than trough, then resultant wave will have a smaller crest If trough is larger than crest, the resultant wave will have a smaller

trough

Interference Applets

Standing Waves

A special occurrence when interference occurs after wave reflection has occurred.

If the incoming wave and reflected wave have just the right frequency, they will produce a combined wave that appears to be standing still.

This combined wave is called a standing wave. So a standing wave is really two waves interfering

as they pass through each other, that appears to be standing still.

Nodes and Antinodes

In a standing wave, destructive interference produces points with no amplitude. These points of zero amplitude on a standing wave are

called nodes. Nodes are always evenly spaced on the standing wave.

Also in a standing wave, constructive interference creates points with great amplitude. These points of maximum amplitude are called antinodes. Antinodes are also ½ between nodes.

Standing Wave Demonstrator

Resonance Most object have a natural frequency.

A swing that is pushed at the swing’s natural frequency allows a small push to create a large increase in the swing’s amplitude.

Standing waves occur when an object vibrates at its natural frequency.

If a nearby object vibrates at the same frequency as an object’s natural frequency, resonance can occur. Resonance is an increase in the amplitude of a vibration

that occurs when external vibrations match an object’s natural frequency.

Can be useful Musical instruments use resonance o create stronger,

clearer sounds.

Resonance can be harmful Tacoma Narrows Bridge