Unit P3 – WavesUnit P3 – WavesLesson 01 – Lesson 01 – Reflection and RefractionReflection and Refraction

Aims:• Understand that light is reflected

from a mirror in a predictable way• Understand the laws of reflection

and refraction

Questions…1. Describe a situation that proves

light travels faster than sound2. What happens to light when it hits

a mirror?

Apr 21, 2023

Amplitude…Amplitude…The height of a wave is known as the AMPLITUDE…

Amplitude

Wavelength

The distance between two waves is known as the WAVELENGTH…

The number of waves hitting the beach each second is known as the Frequency

Speed of Waves…Speed of Waves…You are standing on the beach…The wavelength is 3m (there are 3 meters between each wave)2 waves hit your feet each second (yes… they are fast waves!)

Distance of water passing your feet each second…= 3m (length between each wave) x 2 (waves per

second)= 6m

Speed of wave = wavelength x frequency= 3m x 2 Hz = 6m/s

Beach…Beach…

3 waves pass Ernie’s feet, 3 waves pass Ernie’s feet, each secondeach second

In one second 3 waves pass Ernie’s feet

2m

0 1 2 3

01

2

3

Frequency……….

Wavelength………

Distance of wave……

Speed of wave………

1. Copy the diagram of the wave…

Label the wavelength and amplitude.2. Copy and complete this table that compares

longitudinal and transverse waves…

3. Are water waves, longitudinal or transverse, draw a diagram to explain.

4. Explain what refraction is.

Feature Transverse Wave Longitudinal Wave

These waves transfer energy

Regular disturbances can be seen

Disturbances move from side to side

Disturbances move forward and back

WhiteWhite light light

Is a mixture of…Red RichardOrange ofYellow YorkGreen GainedBlue BattlesIndigoinViolet vain

• A prism will split white light up into the seven colours

• Raindrops will also split up light, we see a rainbow if the weather is sunny and rainy.

Things to do…• AQA Text book, page 314-315. Copy diagram of

electromagnetic spectrum. Use two pages and give an example/diagram and use of each type of electromagnetic radiation.

• E.g.

X -Rays

Taking pictures of

bones

Echo-LocationEcho-Location

Ships use SONAR

Question…• Speed of sound in water = 1500 m/s• An echo takes 4 seconds to bounce off the sea,

bed how deep is the sea?

Answer…• Distance = speed x time = 1500 m/s x 3s = 6000 m• But this is the total distance, the

sound wave travels. [to the sea bed and back].

• Depth = 6000m ÷ 2 = 3000m

Analogue and DigitalAnalogue and DigitalAnalogueNormal soundsA constantly changing signal. Easy to receive and interpretSignal quality gets lower over long distance

DigitalInformation on a CDA series of zero’s and one’s (on / off)Signal must be converted into 1’s and 0’s, and then back againData is tranferred easily as even if quality of signal degrades it is easy to tell if the signal is on (1) or off (0)

Converting from Analogue to Converting from Analogue to DigitalDigital

Time / s

Voltage / V

Analogue > Digital

Analogue wave

0

642 8 10 12 16140

10

20

30

40

50

60

Time / s

Voltage / V

Analogue > Digital

Fit digital signal over wave

0

642 8 10 12 16140

10

20

30

40

50

60

Time / s

Voltage / V

Analogue > Digital

Voltage conversion…

0

642 8 10 12 16140

10

20

30

40

50

60

7 17 28 36 43 47 50 50 46 35 28 26 24 22 18 17

Time / s

Voltage / V

Analogue > Digital

Digitise signal…

0

642 8 10 12 16140

10

20

30

40

50

60

7 17 28 36 43 47 50 50 46 35 28 26 24 22 18 17

Raw Data 7 17 28 36 43 47 50 50 46 35 28 26 24 22 18 17

Maximum value = 50, so send data in chunks of 50 numbers…

7= 1111111000 0000000000 0000000000 0000000000 0000000000

17= 1111111111 1111111000 0000000000 0000000000 0000000000

28= 1111111111 1111111111 1111111100 0000000000 0000000000

Etc…

The data is sent as a series of 1’s and 0’s (on /off), but first a message must be sent to inform the receiver to accept data in chunks of 50

At the receiver the data is converted back into a signal of baring voltage…

At the Reciever…At the Reciever…

• First a message is received telling the receiver to accept data in chunks of 50…

1111111000 0000000000 0000000000 0000000000 0000000000 =71111111111 1111111000 0000000000 0000000000 0000000000 =171111111111 1111111111 1111111100 0000000000 0000000000 =28

Then the data is put together…

Time / s

Voltage / V

Digital > Analogue

Put the wave back together…

0

642 8 10 12 16140

10

20

30

40

50

60

7 17 28 36 43 47 50 50 46 35 28 26 24 22 18 17

Time / s

Voltage / V

Digital > Analogue

Wave…

0

642 8 10 12 16140

10

20

30

40

50

60

7 17 28 36 43 47 50 50 46 35 28 26 24 22 18 17

Time / s

Voltage / V

Digital > Analogue

Wave…

0

642 8 10 12 16140

10

20

30

40

50

60

7 17 28 36 43 47 50 50 46 35 28 26 24 22 18 17

Original analogue signal

Time / s

Voltage / V

Digital > Analogue

Wave…

0

642 8 10 12 16140

10

20

30

40

50

60

7 17 28 36 43 47 50 50 46 35 28 26 24 22 18 17

The new signal is not an exact copy, but quite close – more samples would make it better quality….

1. Speech is an analogue form of communication. Giving someone a ‘Thumbs-up’ is digital. Describe some other forms of digital communication.

2. Give two advantages of transmitting television signals via digital fibre optic, rather than analogue waves.

3. The diagram shows a bar-code. It is a series of thick and thin black stripes. Is that an analogue or digital signal – explain your answer.

4. The diagram shows an analogue sound wave. Copy the diagram, but add a digital signal that would sound the same.

5. Compact discs store music digitally. There are 44 000 samples each second. New (super audio) CD discs have 192 000 samples each second. Explain how this will reproduce the sound wave more accurately.