Review: What’s the difference between a transverse and longitudinal wave? What do waves transfer? What are the high and low points of a transverse wave.

Review:What’s the difference between a transverse

and longitudinal wave?

What do waves transfer?

What are the high and low points of a transverse wave called?

What are the parts of a longitudinal wave where the particles are spread out and close

together?

First thing’s first…• Which of these show ONE full wave?

One wave has one crest and one trough

Wavelength• What is length a measure of?• So what do you think a wave length

is?– The distance between two wavesWAVELENGTH

WAVELENGTH

Which has a shorter wavelength?

Measuring Wavelength• Does this tell us the distance

between the two waves?• Why not?

You have to measure the distance between two comparable points!

(crest to crest, trough to trough, etc.)

Amplitude• The distance between the crest or

trough and the wave’s resting position.

• Where’s the crest? Trough?

Resting Position

Trough

Crest

Am

plitu

de

Am

plitu

de

Which has a larger amplitude?

What does amplitude tell us about a wave?

• Which of these waves would cause more damage if it hit the shore?

• Which has the larger amplitude?• Which wave has more energy?

THAT’S AMPLITUDE!

We’ve been looking at transverse waves…What about

longitudinal?• We can relate all of the parts of a

transverse wave to a longitudinal one!

We’ll start with wavelength…

• In a transverse wave:

• But there aren’t any crests or troughs in a longitudinal wave!

WAVELENGTH

WAVELENGTH

So we look at the compressions and rarefactions!• Compressions =

Crests• Rarefactions =

Troughs• Now we can find

the wavelength– Compression to

compression – Rarefaction to

rarefaction

On to amplitude…• In a transverse wave:

• We now know that compressions and rarefactions are like the crests and troughs, but it’s hard to find a longitudinal wave’s resting point.

Amplitude• For the amplitude

of a longitudinal wave, we look at how compressed or how rarefied the spring or particles are.– The more

compressed or rarefied it is, the higher the amplitude and vice versa.

Frequency• If your friend comes over to your

house “frequently”, how often do they come over?

• Can you take a guess as to what the “frequency” of a wave is?– The frequency of a wave tells us the

number of waves that are produced in a certain amount of time.

We need to know how many waves are being produced in

10 seconds.• How can you find the frequency of

this wave?• Step 1: pick a point.• Step 2: count the waves that pass

that point in 10 seconds.

Which has a higher frequency?

What about Energy?

Which wave did you have to put more energy into to create?

Waves with _________________frequency have

more energy.

What is the unit for frequency?

• Frequency is measured in Hertz (Hz).• If one full wave passes a point every

second, it has a frequency of 1 Hz.– 1 wave per second (1 wave/1 sec.)

• What is the frequency if three waves pass a point every second? – 3 Hz. (3 waves/1 second)

• What is the frequency if six waves pass a point every three seconds?– 2 Hz. (6 waves/3 seconds)

Wave Speed• There are two ways to calculate

wave speed.– Option 1: time how long a wave takes to

get from point A to point B.

A B

• Option 2: Use the following formula

Wave speed = wavelength x frequency

Wavelength – 2 meters

Frequency – 4 Hz.

(4 waves pass every second)

Wave Speed = 8 meters/second

• Wave speed is affected by several factors– The type of wave

• Example: electromagnetic waves always travel at the same speed in a vacuum (300,000 km/s – the speed of light)

– The medium the wave is moving through• If you start two waves in a pan, one with

water and one with corn syrup, which will reach the other side of the pan first?

• Another example is popping your knuckles underwater as opposed to above water.

Reflection

• Law of Reflection– The angle of incidence

equals the angle of reflection

Image position

• You think in straight lines!

• The image is located behind the mirror.

Refraction

• Sudden change in direction of a wave as it changes speed.– It must enter obliquely to change direction!

• Which direction does it bend as it slows?

Refraction

• In both cases the speed of the wave has decreased. This is indicated by the decrease in wavelength!

Refraction

• In which medium does light travel faster? (glass rod appears bent)

Refraction

• In simple terms, refraction is caused when a wave moves from one type of medium to another that has a different density. This makes objects between them look different.