Sound and LightSound and Light Spectra of Science Amole 2013

Sound Waves Produced from vibrating particles – Particles “bump” into each other to transfer the energy through the medium Travel in longitudinal waves Travel in all directions (like a circle) Can travel through solids, liquids, and gases – Faster in solids and liquids than gases Cannot travel in a vacuum (through empty space)

Sound Examples Percussion instruments have vibrating membranes String instruments have vibrating strings Woodwinds have vibrating reeds Brass instruments vibrating lips Your vocal cords are two thin elastic bands that vibrate – Say “ahhhhh” and touch your throat. Feel them?

Pitch How high or low a sound is Determined by frequency of the sound wave Frequency is determined by how quick or slow the particles vibrate Quick Vibration High Frequency High Pitch Slow Vibration Low Frequency Low Pitch Notice: High frequencies have shorter wavelengths.

Intensity Determines the “loudness” of the sound Intensity decreases with distance from the sources as it spreads out Depends on the amplitude of the sound Higher amplitudes produce louder sounds Louder Softer Notice: The wavelength and frequency are the same. Only amplitude changed.

Hearing Sound: The Ear 1.Sound causes your eardrum to vibrate. The eardrum vibrates differently for each sound. 2.The bones of your ear begin to vibrate, beginning with the hammer, moves to the anvil, and finally the stirrup Eardrum 3 bones: hammer, anvil, and stirrup

Hearing Sound: The Ear 3.The sound energy passes to the inner ear. This causes the fluid in the cochlea to move. 4.The nerves then carry the message to the brain. Your brain then tells you what the sound is. Outer Ear Cochlea Inner Ear

How the Ear Works

Producing Sound: The Vocal Chords 1.Air from the lungs flows through the windpipe and into the voice box (where the vocal cords are). 2.Then the air pushes the vocal cords apart making them vibrate. 3. The vibrations create a series of sound waves that exit through your mouth.

Producing Sound: The Vocal Chords 4.The change of shape of the vocal cords changes the sound and its pitch. 5.If you can’t talk because of a cold or laryngitis, it is because your vocal cords are swollen and inflamed.

Vocal Folds

Vocal Folds (Slow Motion)

More About Sound Sonar- Sound Navigation And Ranging – Determine distance by measuring the time it takes for sound waves to be reflected back – Used by ships, submarines, and bats Ultrasound – Use echos to produce images called sonograms of inside the body without performing surgery

Did You Know? Sound waves that are reflected off boundaries are called “echos.” Sound travels 4 times faster in water than air. Any frequency of sound below the range of human hearing (20 Hz) is called Infrared sound. Any frequency of sound above the range of human hearing (20, 000 Hz) is called Ultrasound.

Doppler Effect Change in frequency of a wave due to relative motion between source and observer. A sound wave frequency change is noticed as a change in pitch.

Doppler Effect

Light Waves “Dual natured” Travel in transverse waves Travel in straight lines in all directions Can travel through some solids, liquids, and gases – Slow down when traveling through a medium Can travel in a vacuum (through empty space) – Consist of changing electric and magnetic fields in space

Where does light come from? Our major light source: the Sun

Electromagnetic Spectrum

Two Models of Light Wave Model – Transverse waves that do not need a medium – Explains why light can reflect, refract, or diffract, interfer with one another, and produce standing waves Stream of Particles Model – Photons- packets of light, localized energy – Explains why blue light can knock electrons off a metal plate but red light cannot, and why light can travel without a medium The model used depends on the situation

Is Light a Wave or Particle?

Energy and Frequency Energy of light is proportional to frequency Higher frequency = more energy

The Speed of Light In a vacuum, all light travels at the same speed – 3 x 10 8 m/s = 186,000 miles/sec – Symbol “c” – Light is the fastest signal in the universe Also can travel through transparent mediums – Air, water, and gas – Travels slower when passing through a medium – More dense = slower speed

Intensity Determines the “brightness” of light Intensity decreases with distance from the sources as it spreads out Depends on amount of light (number of photons or power passing through)

Intensity

How Light Travels  Light rays travel in straight lines from the light source.  When it hits an opaque object, some light is absorbed and the rest reflects off.  If the object is transparent, light rays pass through it easily.  If the object is translucent, some light can pass through, but the rest of the light will be reflected.

Reflection Angle of incidence Angle of reflection The ‘angle of reflection’ is always equal to the ‘angel of incidence’. on off

Seeing Color The colour an object appears depends on the colours of light it reflects. For example, a red book only reflects red light: White light Only red light is reflected

Colors White light can be split up to make separate colours. These colours can be added together again. The primary colours of light are red, blue and green: Adding blue and red makes magenta (purple) Adding blue and green makes cyan (light blue) Adding all three makes white again Adding red and green makes yellow

A white hat would reflect all seven colours: A pair of purple trousers would reflect purple light (and red and blue, as purple is made up of red and blue): Purple light White light

Color

Refraction Waves travel different speeds in different mediums When waves change mediums, their speed changes causing the waves to bend

Diffraction  Light rays travel in straight lines, radiating out from the light source.  If rays are blocked by an opaque object a shadow forms where the light cannot reach.  If the light source is moved closer to the object, more light is blocked and a larger shadow is formed. light source light source

Shadows 6am 8am 9am 12am 2pm10am 3pm 4pm 7pm Looking North, the Sun appears to rise in the East......and travel across the sky until it sets in the West. The position of the Sun effects the position and length of the shadows created. Thanks to this natural phenomenon a sundial is able to tell us the time, as long as it is a sunny day!

Seeing Light: The Eye 1.Light coming from, (or reflecting off) objects enters the eye through the cornea then the pupil. 2.It is focused clearly by the lens on to the retina. 3.The light sensitive cells of the retina gather information about patterns of light and dark, color and movement and send it through the optic nerve.

Seeing Light: The Eye 3.Information entering the brain through the optic nerve, is then transmitted through more nerve pathways to the visual cortex. 4.Here the patterns of light and dark, colour and movement are interpreted. 5.The brain, based on past experience, can then understand what it ‘sees’.

How the Eye Works

More about Light Sunlight contains ultraviolet and infrared – UV will burn you, IR warms you X-rays and gamma rays are high frequency light waves used in medicine Microwaves are used in cooking and communication (mobile phones) Radio waves are used in communication and radar – Radar: Radio Detection And Ranging – Uses reflected radio waves to determine velocity and location

Did You Know? Rainbows are the refraction of white light through water droplets that reflect them back in the air. Fiber optics operate on total internal reflection. The interference of light waves create the rainbow swirls on bubbles. The light we see from the sun is 8 minutes old. It takes light 8 minutes to travel from the sun to Earth even at its fast speed.