1. Waves

2. Menu Recap of KS3 Light Reflection Diffuse & Regular Reflection
Refraction
Total Internal Reflection
Waves
The Electromagnetic Spectrum

3. Light Travels in Straight Lines
Which direction is the Sun?
Sun
Remember….Light travels in straight lines!

4. HOW FAST IS LIGHT?
It is the fastest thing in the universe. It travels at 300,000 kilometres per second.
At this speed it can go around the world over 7 times in just one second.

5. Light Travels Faster Than Sound.
Thunder and lightning start at the same time, but we will see the lightning first.
The light & sound happen at the same time when a firework explodes

6. We see things because the light is reflected into our eyes
(The sun is different – it produces its own light.)

7. What is a shadow?
Shadows are places where light is blocked

8. Summary of Light Light travels in straight lines
Light travels much faster than sound
We see things because light is reflected into our eyes
Shadows are formed when light is blocked by an object
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9. Reflection

10. How is light reflected from a mirror?
Normal
Incident Ray
Reflected Ray
Angle of Incidence
Angle of Reflection
Plane Mirror

11. Is there a law to explain reflection?
Angle of incidence = Angle of reflection
500
500

12. Regular Reflection
Smooth, shiny surfaces like mirrors give ‘regular’ reflection

13. Diffuse Reflection
Rough, dull surfaces like a table top give ‘diffuse’ reflection. This is where light is scattered in all directions.

14. What ‘type’ of reflection can you see?
Diffuse reflection
Clear Reflection

15. What are mirrors used for?
Periscopes

16. What are mirrors used for?
Car headlights
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17. Refraction

18. Refraction
Refraction happens when waves change speed as they travel through a different medium.
The light rays are slowed down by the water and are refracted, causing the pencil to look ‘broken’. What are the 2 mediums in this example?

19. Why is it so difficult to spear fish?
Diamonds & prisms use the property of refraction.

20. How is light refracted in a glass block?
Air
Bends towards normal when entering a MORE dense medium
Glass
Air
Displacement
Bends away from normal when entering a LESS dense medium

21. What happens if light approaches along ‘NORMAL’?
Air
Glass
Air
The light ray isn’t deviated from its position even though it slows down in glass and speeds up in air.

22. Angle of incidence the SAME as critical
Angle of incidence LESS than critical
Angle of incidence GREATER than critical results in TOTAL INTERNAL REFLECTION

23. Angle of incidence LESS than the critical angle
Angle of incidence GREATER than critical angle

24. Total internal reflection can turn a prism into a mirror!

25. The special property of TOTAL INTERNAL REFLECTION is used in OPTICAL FIBRES
Uses of Optical Fibres include:
Communication
Endoscopes (the Magic Eye)
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26. What is a Wave?
All waves carry energy without transferring matter. Light, infra red, and microwaves all make things warm up (which shows that they can carry energy).
Loud sounds can make things vibrate or move. Even the quietest sound can move your ear drum.

27. Waves can be…. reflected refracted diffracted
Waves are split into 2 types:-
LONGITUDINAL (like sound)
TRANSVERSE (like light)

28. Longitudinal Waves SOUND IS A LONGITUDINAL WAVE
Direction of wave Travel
Vibrations
In Longitudinal waves the VIBRATIONS are along the SAME DIRECTION as the Wave is Travelling
SOUND IS A LONGITUDINAL WAVE

29. Transverse Waves Most Waves are Transverse. LIGHT IS A TRANSVERSE WAVE
Direction of Wave Travel
Most Waves are Transverse. LIGHT IS A TRANSVERSE WAVE
Vibrations are at right Angles to Direction of Travel

30. This is a Transverse Wave on a ‘Wave Machine’

31. Describing Waves
Vertical
displacement
Amplitude
Horizontal
Displacement
Amplitude
THE AMPLITUDE shows the displacement of the particles. It is related to energy

32. Describing Waves THE WAVELENGTH is a full cycle of the wave Wavelength
Vertical
displacement
Wavelength
Horizontal
Displacement
THE WAVELENGTH is a full cycle of the wave

33. Describing Waves
Vertical
displacement
Time
THE PERIOD is the time taken for 1 complete cycle. (Notice the change in the horizontal axis)

34. Frequency
The frequency is the number of waves that pass a set point each second
It is measured in hertz (Hz)

35. The Wave Equation
Speed Frequency & Wavelength are all linked together using the following equation:-
SPEED = FREQUENCY x WAVELENGTH
m/s Hz m

36. 3 waves travel at the same speed but have different frequencies & wavelengths. Complete the Table
(m/s)
Frequency
(Hz)
Wavelength
(m)
Wave 1 16 8
Wave 2 32
Wave 3 2
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37. The Electromagnetic spectrum

38. The Electromagnetic Spectrum
Visible
Radio Waves
Micro-waves
Infra Red
Gamma
rays
U.V
X-rays
Longest Wavelength
Lowest Frequency
Lowest Energy
Shortest Wavelength
Highest Frequency
Highest Energy

39. The Electromagnetic Spectrum
All E.M. waves have the same properties of light. They can all:
Travel at the speed of light
Be Reflected
Be Refracted
Travel through a vacuum as a transverse wave

40. The E.M Spectrum
The properties change as the wavelength (or frequency changes) There are 7 basic types:
* Radio waves * Microwaves
* Infra Red * Visible
* Ultra Violet * X-Rays
* Gamma Rays

41. Radio Waves
Used mainly for communication

42. Microwaves Microwaves have 3 main uses: for cooking food rapidly
Satellite Transmission
Mobile phone communications

43. Infra Red:
Otherwise known as Heat Radiation. It is given out by all hot objects.
We feel it on your skin as radiant heat.
Used for night-vision equipment and in remote controls for TVs.

44. Some Examples of Infra Red Radiation
Can you think of examples where Infra Red photography is useful to us? Look at the photographs for clues

45. Fire Fighters Use Infra Red Cameras to Find People in Situations Where They Can’t Rely on Their Eyesight

46. Visible Light (ROYGBIV)
This is the ONLY light from the E.M. spectrum that our eyes can detect.
We use colour to send signals.
They are used in Optical Fibre Digital Communications

47. The colours of the rainbow:
Red
Orange
Yellow
Green
Blue
Indigo
Violet

48. Ultraviolet (U.V.) Used to:
Detect forgeries
Find hidden security marks
Make clothes glow ‘whiter than white!’
Make your teeth appear whiter
Give us a suntan
Kill insects
Dangerous – can cause cancer and make you blind!

49. Ultra Violet Light can cause fluorescence

50. X-Rays: We use X-rays to: Detect broken bones
To ‘screen’ bags for bombs, guns etc at airports.

51. This X Ray is being used to ‘look inside’ the coffin of a mummy without ‘opening’ it

52. Gamma Radiation:
Gamma rays are VERY dangerous. In high doses, Gamma rays (along with X-rays and U.V. rays) can kill normal cells.
Used to:
Kill harmful bacteria in food to keep it fresher for longer.
Sterilise medical instruments.
Treat cancer.

53. Complete the Table As Comprehensively As Possible on the Next Slide

54. Hazards of using E.M. Radiation
Type of E.M. Radiation
Source of E.M. Radiation
Uses of E.M. Radiation
Hazards of using E.M. Radiation
Radio Waves
Microwaves
Infra Red
Visible
Ultraviolet
X Ray
Gamma Ray

55. Questions on the E.M. Spectrum
1). Name a type of electromagnetic wave that:
Is visible to the naked eye.
Is emitted by hot objects
Can cause fluorescence.
Can pass through dense metals.
2). Give 3 properties common to all electromagnetic waves.
3). Put the following in order of wavelength, starting with the longest: ultraviolet, X-rays, red light, microwaves, infrared.
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