Chapter 14: WavesSection 1: Types of Waves

Most of us picture waves of water splashing on a shore when we hear the word…

However, waves are found in other forms.

• Definition: wave – a periodic disturbance that transmits energy.

• Waves are periodic, which means that they occur one after another in a pattern.

For example…the periodic table list elements one after another in a pattern.

Its easy to see that these ocean waves are periodic…

Waves are a method of energy transfer, and come in several types.

– Definition: mechanical wave – a wave that requires a medium to travel.

•Definition: medium – any type of matter that can support a wave.

Waves can be classified according to how they move…

– Definition: transverse wave – a wave that causes a medium to move perpendicular to the wave’s motion.

Medium

Direction of Wave

TRANSVERSE Wave

– Definition: longitudinal wave – a wave that causes a medium to move parallel to the wave’s motion.

They are also called “compressional waves”.Why? Because they cause the medium to

compress, or squeeze together.

Direction of Wave

LONGITUDINAL Wave

– All mechanical waves are caused by the vibrations of a medium

Some waves do not need a medium in order to transmit energy…

• Definition: electromagnetic wave – a wave that does not require a medium to travel.

– EM Waves can travel through outer space• There is no medium in outer space…

• Some examples of EM waves:– Sunlight

– UV Rays

– Nuclear Radiation

– Lasers

• Some uses of EM waves:– Radio– Television– Satellite– GPS Navigation– Telephones– Fiber Optics– Medicine– And on and on and on…

Chapter 14: WavesSection 2: Characteristics of Waves

• Crest – the highest point of a transverse wave and the area of highest energy.

• Trough – the lowest point of a transverse wave.

Wave Properties

– Amplitude – the vertical distance that a wave moves particles.

– Wavelength – the distance between two troughs of a wave. (meters)

Wave Properties

•Water waves with a large amplitude are great for surfing!

•They also carry more energy!

– The amplitude of a wave tells how much energy it is carrying.

– The bigger theamplitude, themore energy the wave has.

Wave Properties

For a longitudinal wave:•Compressions are like crests.•Rarefactions are like troughs.

Compression Rarefaction

• Wave Period – the time it takes for one full wavelength to pass a point.– Waves with longer wavelength’s have a longer

period.

•Frequency – the number of wavelengths that pass in a certain time period.•Measured in Hertz

(Hz)

Waves with higher frequency transfer more energy.

Which Wave has the higher frequency?

Mechanical waves travel best through solids, and worst through gases.

Because a solid’s atoms are tightly bonded, a vibration is quickly passed between atoms.

ENERGY

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• Definition: Doppler Effect – the change of a wave’s frequency caused by motion.

How does the sound of a siren change as a car passes by you?

• If the wave source away from you, the frequency seems lower.

• Why? You’re being hit with more wave each second.

• If the wave source moves toward you, the frequency seems higher.

Why? You’re being hit with more wave each second.

Chapter 14: WavesSection 3: Wave Interactions

Waves are energy, plain and simple.When a wave moves from one medium to another,

some of the wave’s energy may be reflected.• Definition: wave reflection – the bouncing

back of a wave when it hits a surface.

– We are able to see because light is reflected off objects and back to our eyes.

Smooth materials reflect waves better

than rough materials.

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Rough materials cause waves to collide and lose energy.

When waves pass the edge of an object, or move through an opening, they bend.

• Definition: diffraction – the bending of a wave when it encounters an obstacle.

•Sound & Light waves diffract when they bend around corners.

• Water waves can be diffracted as well.

• Notice how the wave changes as it passes through the opening.

When a wave passes into a new medium, it can bend.

• Definition: refraction – the bending of a wave as it passes into a different medium.

Refraction causes a wave to change its speed.

Is the spoon really broken? Of course not!

Light entering the water bends, and the image that we see is bent as well!

Light refraction can “break” white light into colors.

Light passes into a new medium, the prism.

The light wave is separated into 7

colors.

• Because waves are made of energy, many of them can exist in the same place @ the same time.

– When multiple waves meet, a new wave is created.

– Definition: wave interference – the process of two or more waves combining to create a new wave.

Wave Interference

–Constructive interference produces a more powerful wave.

– If the waves interfere with each other at the right time, they will combine to form a larger wave.

Types of Interference

– Destructive interference produces a wave that is weaker.

– When 2 opposite waves interfere, they will weaken each other. If they are exactly opposite, they’ll cancel out!

Types of Interference