Waves

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.)

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

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 Return to Menu

Reflection

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

Is there a law to explain reflection? Angle of incidence = Angle of reflection 50 0

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

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

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

What are mirrors used for? Periscopes

What are mirrors used for? Car headlights Return to Menu

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?

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

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 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

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

Total internal reflection can turn a prism into a mirror!

The special property of TOTAL INTERNAL REFLECTION is used in OPTICAL FIBRES Uses of Optical Fibres include: Communication Endoscopes (the Magic Eye) Return to Menu

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

This is a Transverse Wave on a ‘Wave Machine’

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

Describing Waves Vertical 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 Equation Speed 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 1168 Wave 232 Wave 32 Return to Menu

The Electromagnetic spectrum

The Electromagnetic Spectrum Radio Waves Micro- waves Infra Red VisibleVisible 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

Radio Waves Used mainly for communication

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

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

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!

Ultra Violet Light can cause fluorescence

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

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

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.

Complete the Table As Comprehensively As Possible on the Next Slide

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. Return to menu