waves. a.electromagnetic energy 1.energy a. def. ability to do work b. everything radiates...

WavesWaves

A. Electromagnetic Energy1. Energy

a. Def. ability to do workb. everything radiates electromagnetic energy

B. Properties of electromagnetic energy1. Electromagnetic energya. Def. – is the energy that has properties of a transverse wave

Crest

Trough

Amplitude

Wavelength

2. Characteristics of a wavea) Crest

top of a waveb) Trough

bottom of a wavec) Amplitude

the height of a wave from center to crestd) Wavelength

distance between two different crestse) Frequency

amount of waves that pass a given point in a certain amount of time

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3. Electromagnetic Spectruma) entire range of electromagnetic wavelengths (ESRT. Pg. 14)

How do electromagnetic How do electromagnetic waves differ?waves differ?

Different electromagnetic waves carry different amounts of energy.

The amount of energy carried by an electromagnetic wave depends on the wavelength: the shorter the wavelength, the higher its energy.

Do microwaves have a shorter wavelength than X-rays?

Wavelength and frequency are linked properties of a wave: the shorter the wavelength, the higher its frequency.

So, frequency also tells you about the energy of a wave: the higher its frequency, the higher the energy.

Part 1 – Properties of Part 1 – Properties of LightLight

Light travels in straight lines:

Laser

Properties of Light Properties of Light summarysummary

1) Light travels in straight lines2) Light travels much faster than sound3) We see things because they reflect

light into our eyes

C. Matter and electromagnetic energy1. Five ways light can acta) Reflect – bounceb) Refract – bendc) Absorb – take ind) Transmit – give offe) Scatter – spread out

We see things because they reflect light into our eyes:

Homework

What happens when What happens when waves hit a surface?waves hit a surface?

How the waves behave depends on their energy and the type of material.

For example, light waves are reflected by skin but X-rays pass straight through.

If electromagnetic waves are absorbed, some of their energy is absorbed by the material. This usually increases the temperature of the material.

Light travels much faster than sound. For example:

1) Thunder and lightning start at the same time, but we will see the lightning first.

Types of Mechanical Waves

• The types based on the way the wave moves.• Transverse

– Medium moves at right angles to the direction of wave movement

– Top = crest; Bottom = trough; middle = rest position– Ex: Rope Wave

• Longitudinal – Medium and wave move in same direction.– Area close together = compression; Area spread out =

rarefaction– Ex: Springs

Transverse/longitudinal Transverse/longitudinal waveswaves

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Sound travels as waves made up of vibrating air particles.

What are longitudinal waves?

PAT ARTWORK PC14_2

Sound waves are an example of longitudinal waves.

In a longitudinal wave, the particles vibrate back and forth, so the direction of their movement is parallel to the direction of the wave.

Think about the hairs on this fluffy cat vibrating backwards and forwards, as sound waves from the speaker pass by!

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What do longitudinal waves look like?

A Slinky can be used to model longitudinal waves, by moving one end of the Slinky left and right.

The wave travels away from the source. The direction of the wave is parallel to the movement of the source.

source movesleft and right

coils vibrateleft and right

direction of wave

In a longitudinal wave, the coils do not travel horizontally; each coil of the Slinky just vibrates left and right.

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Certain parts of a longitudinal wave have special names.

compression

rarefaction

What are the parts of a longitudinal wave?

Sound waves are longitudinal waves. When someone speaks, the air particles vibrate as a longitudinal wave, and so compressions and rarefactions are formed in the air.

P waves, the primary waves produced by earthquakes, are also longitudinal waves, which push and pull the Earth.

Sections that are pushed together are called compressions, and sections that are stretched out are called rarefactions.

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Simulation of a longitudinal wave

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The wavelength of any wave is the distance between two matching points on neighboring waves.

Wavelength of a longitudinal wave

wavelength

wavelength

The wavelength is the same whichever two matching points are used to measure this distance.

The symbol used to represent wavelength is .

Wave AnimationWave Animation

https://youtu.be/Rbuhdo0AZDU

Color• Color you see is the wavelength of color

the object reflects.• Primary Colors

– Three colors used to make every other color.

– Red, Green, Blue• Secondary Colors

– Two primary colors mixed in equal amount.

• White light (all colors mixed)

ColorColorWhite light is not a single color; it is made

up of a mixture of the seven colors of the rainbow.

We can demonstrate this by splitting white light with a prism:

This is how rainbows are formed: sunlight is “split up” by raindrops.

The colors of the rainbow:The colors of the rainbow:

RedOrangeYellowGreenBlue

IndigoViolet

A white hat would reflect all seven colors:

A pair of purple pants would reflect purple light (and red and blue, as purple is made up of red and

blue):

Purple light

Whitelight

Sound

• Begins with a vibration• Travels longitudinally through a medium

(solid, liquid or gas)• Humans make sound by vibrating vocal

cords found in the larynx.• Due to diffraction sound can bend

around corners.

Drawing sounds…Drawing sounds…

This sound wave has a _____ frequency:

This sound wave has a ___ _frequency:

Drawing sounds…Drawing sounds…

This sound wave has a _____ amplitude (loud):

This sound wave has a _____ amplitude (quiet):

Resonance

• Resonance• Most objects naturally vibrate.• When a wave passes through a material

at the same frequency as the natural vibration.

• Can cause the natural object to start vibrating more strongly.

You Tube video

http://www.youtube.com/watch?v=IZD8ffPwXRo&feature=rec-LGOUT-real_rn-HM

https://www.youtube.com/watch?v=urYWaHfel6g

A sound can be quiet or loud.Loudness and amplitudeLoudness and amplitude

On an oscilloscope trace, the loudness of a sound is shown by the height of the wave. This is called the amplitude. Which word should be crossed out in this sentence:

The larger the amplitude of the wave on the trace, the louder/quieter the sound.

quiet sound loud sound

A sound can be high or low – this is the pitch of the sound.Pitch and frequencyPitch and frequency

On an oscilloscope trace, the pitch of a sound is shown by how many waves there are. This is called the frequency. Which word should be crossed out in this sentence:

low pitch high pitch

The greater the frequency of the waves on the trace, the lower/higher the pitch.

Which trace represents the loudest sound?Which wave is the Which wave is the

loudest and highest?loudest and highest?Sound A has the largest amplitude (i.e. the tallest waves), so it is the loudest of these two sounds.

Which trace represents the sound with the highest pitch?

Sound B has the greater number of waves across the oscilloscope – it has the highest frequency and so has the highest pitch.

A B

A B

Amplitude and Amplitude and wavelengthwavelength

Describing sound wavesDescribing sound waves

Sound waves summarySound waves summary

Doppler Effect

• The apparent change in frequency as a wave source changes position relative to the listener.

• Move towards listener = higher pitch.– Waves reach listener with a higher

frequency.• Move away from listener = lower pitch.

– Waves reach listener with a lower frequency.

Doppler EffectDoppler Effect

Doppler Effect

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What is the Doppler effect?

Doppler VideosDoppler Videoshttps://www.youtube.com/watch?v=z0EaoilzgGE https://www.youtube.com/watch?v=h4OnBYrbCjY