waves. menu recap of ks3 light reflection diffuse & regular reflection refraction total internal...
TRANSCRIPT
Menu• Recap of KS3 Light
• Reflection
• Diffuse & Regular Reflection
• Refraction
• Total Internal Reflection
• Waves
• The Electromagnetic Spectrum
Light Travels in Straight Lines
Which direction is the Sun? Remember
….Light travels in straight lines!
Sun
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.
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
We see things because the light is reflected into our eyes
(The sun is different – it produces its own light.)
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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How is light reflected from a mirror?
Incident Ray
NormalReflected
RayAngle of
IncidenceAngle of
Reflection
Plane Mirror
Rough, dull surfaces like a table top give ‘diffuse’ reflection. This is where light is scattered in all directions.
Diffuse Reflection
RefractionRefraction 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?
Air
Glass
Air
Bends towards normal when entering a MORE dense medium
Bends away from normal when entering a LESS dense medium
Displacement
How is light refracted in a glass block?
Air
Air
Glass
What happens if light approaches along ‘NORMAL’?
The light ray isn’t deviated from its position even though it slows down in glass and speeds up in air.
Angle of incidence LESS than critical
Angle of incidence the SAME as critical
Angle of incidence GREATER than critical results in TOTAL INTERNAL REFLECTION
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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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.
Waves can be….• reflected
• refracted
• diffracted
Waves are split into 2 types:-
LONGITUDINAL (like sound)
TRANSVERSE (like light)
Longitudinal WavesDirection of wave Travel
In Longitudinal waves the VIBRATIONS are along the SAME DIRECTION as the Wave is Travelling
SOUND IS A LONGITUDINAL WAVE
Vibrations
Transverse WavesDirection of Wave Travel
Vibrations are at right Angles to Direction of
Travel
Most Waves are Transverse. LIGHT IS A TRANSVERSE WAVE
Describing Waves
Amplitude
Horizontal
Displacement
Vertical
displacement
Amplitude
THE AMPLITUDE shows the displacement of the particles. It is related to energy
Describing WavesVertical
displacement
THE WAVELENGTH is a full cycle of the wave
Horizontal
Displacement
Wavelength
Describing Waves
Time
Vertical
displacement
THE PERIOD is the time taken for 1 complete cycle. (Notice the change in the horizontal axis)
Frequency
The frequency is the number of waves that pass a set point each second
It is measured in hertz (Hz)
The Wave EquationSpeed Frequency & Wavelength are all linked together using the following equation:-
SPEED = FREQUENCY x WAVELENGTH
m/s Hz m
3 waves travel at the same speed but have different frequencies & wavelengths. Complete the Table
Speed(m/s)
Frequency(Hz)
Wavelength
(m)
Wave 1 16 8
Wave 2 32
Wave 3 2
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The Electromagnetic SpectrumRadio Waves
Micro-waves
Infra Red
Visible
U.V
X-rays Gamma
rays
• Longest Wavelength
• Lowest Frequency
• Lowest Energy
• Shortest Wavelength
• Highest Frequency
• Highest Energy
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
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
The E.M Spectrum
Microwaves Microwaves have 3 main uses:
• for cooking food rapidly
•Satellite Transmission
•Mobile phone communications
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.
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
Fire Fighters Use Infra Red Cameras to Find People in
Situations Where They Can’t Rely on Their
Eyesight
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
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!
Gamma Radiation:Used to:
• Kill harmful bacteria in food to keep it fresher for longer.
•Sterilise medical instruments.
•Treat cancer.
Gamma rays are VERY dangerous. In high doses, Gamma rays (along with X-rays and U.V. rays) can kill normal cells.
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
Questions on the E.M. Spectrum
1). Name a type of electromagnetic wave that:
a. Is visible to the naked eye.
b. Is emitted by hot objects
c. Can cause fluorescence.
d. 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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