Ljud och Ljus 8A: Sound and Light

Ljud och Ljus 8A

• The slide deck is for "Ljud och Ljus 8A" (Sound and Light 8A)
• The first lecture was on February 11, 2025, and covered the basics of sound and light
• The second lecture was on February 14, 2025, covering sound
• The third lecture took place on February 18, 2025, covering light
• The forth lecture occured on February 20, 2025, covering colors
• The fifth lecture occured on February 21, 2025, covering the properties of light
• The sixth lecture occured on March 4, 2025, covering experiments with light
• The seventh lecture occured on March 6, 2025, covering experiments with laser light
• The eighth and final lecture occured on March 7, 2025, covering lab reports
• The nineth occurred on March 11, 2025, covering the function of the eye

What is Sound? (Pages 78-103)

• Sound is a change in pressure
• Sound is a pressure wave transported through materials by molecular vibrations
• Sound is created by vibrations

Sound Waves

• Variations in material density( Förtätning och förtunning) create wave motion
• Amplitud is the height of the wave
• Våglängd is the length of the wave
• Vågdal is the trough of the wave
• Vågtopp is the crest of the wave

Wavelength and Amplitude

• Wavelength determines if a tone is light/high or dark/low
• Examples:
  • A mouse squeaks high
  • A whale sings low
• Amplitude determines how strong or weak a sound is
• Wavelength is measured in Hertz (Hz)
  • Humans can hear tones between 20 and 20,000 Hz
• Amplitude is measured in decibels (dB)
  • Sound levels of over 120 dB can cause hearing damage

Properties of Sound

• Echo
  • Sound bounces back from hard objects and can be used for measuring distance
• Applications of Echo
  • Ultrasound
  • Radar
  • Sonar (Ekold)
• Capturing reflected sound can create images of surroundings and inside bodies

Resonance

• Sound resonates; sound waves of the same frequency amplify each other
• Guitars use resonance to amplify string sounds

Consequences of Sound as a Wave

• Sound travels at 340 m/s through the air
• Sound travels faster through solids than air
• There is no sound in space

Doppler Effect

• The frequency changes when a sound source moves relative to the listener
• A race car sounds sharper as it approaches and duller as it moves away

The Sound Barrier

• The Doppler effect plays a role as planes fly faster than the speed of sound
• When a plane approaches the speed of sound, all sound waves compress
• This creates a loud "supersonic boom"

What is Light? (Pages 199-207)

• Light requires an energy source
• Electrons jump to higher energy levels farther from the nucleus
• Light is created when an electron falls back towards the nucleus, releasing energy as a photon

Radiation

• Light is a form of radiation containing energy
• Light is electromagnetic radiation

Wavelength and Color

• Radiation has different wavelengths, which determine color
• Visible light's colors, from longest to shortest wavelength: red (665 nm), orange (630 nm), yellow (600 nm), green (550 nm), blue (470 nm), indigo (425 nm), and violet (400 nm)
• The spectrum includes more than just visible light

Color

• Objects appear colored by reflecting certain light wavelengths
• A blue object reflects blue light and absorbs other colors
• Darker objects absorb more light

White and Black in the Sun

• White objects reflect almost all light/energy
• Black objects absorb almost all light/energy
• White objects stay cool in the sun
• Black objects heat up in the sun

Properties of Light (Pages 182-193)

• Light can be converted to heat when absorbed
• Light travels in a straight path
• Light can be reflected and refracted

Refraction (Pages 188-189)

• Light changes direction when it moves from one medium to another
• Light travels at different speeds in different mediums
• The denser the medium, the slower light travels
• Light travels at 300,000,000 m/s in a vacuum

Refraction Angle

• Light bends towards the normal when moving to a denser medium
• Light bends away from the normal when moving to a less dense medium

How the Eye is Tricked

• Refraction can trick the eye; where one sees a fish in water is not its actual location

Reflection (Pages 184-187)

• Light bounces off surfaces
• Objects are seen thanks to diffuse reflection.
• Reflections occur when light beams bounce back at the same angle creating a mirror image

Reflection Law

• The angle of incidence equals the angle of reflection
• Reflections/mirror images are virtual, not real

Light Trapped Between Reflective Surfaces

• Passing light through an object makes it invisible from the outside
• This occurs in fiber optics or a water stream

Experiment - Bending Light

• Shining a laser through a water stream will cause the light to appear to bend

New Concepts

• Konvergent: Convergent
• Divergent: Divergent
• Parallel: Parallellt
• Convex: Konvex
• Concave: Konkav
• Fokus: Focus
• Brännpunkt: Focal point

Explanation of Concepts

• Konvergent: Convergent beams meet
• Divergent: Divergent beams separate
• Focal point (Fokus): the point where light rays meet

Lens Types

• Sammanslin: A converging lens; the light rays converge on a focal point
• Spridningslins: A diverging lens; the light rays diverge outwards

Brännpunkt

• Brännpunkt/Focus: The point where light rays converge

Mirrors

• Concave mirrors collect light at a focus
• Convex mirrors spread light, appearing to reflect it outwards

Laser Experiment

• Experiments will involve working in small groups with a laserbox
• The laserbox include a protractor and/or plexiglas figures
• The groups must explore how light is refracted/reflected
• Groups must describe their observations; use the concepts from previous slides

Lab Report Guidelines

• State the research question
• List the required materials
• Describe the procedure
• The execution of experiment
• State any observations and documentation
• Provide analysis using physics concepts to explain the outcome
• List any possible fault factors

The Eye

• Eye lenses focus images onto the retina
• The retina has light-sensitive neurons that send signals to the brain

Eyeglasses

• Eyeglasses are needed when images focus in front of or behind the retina
• Additional lenses help images focus correctly

Optics

• Optics used include:
  • Glasses
  • Microscopes
  • Lenses(eyes, cameras)
  • Car mirrors
  • Telescopes

Checklist of Concepts

• Sound is a wave
  • What moves?
  • Frequency/amplitude definition
  • Units of measurement
• Sound properties
• Sound-related phenomena
• Light is a wave
  • What moves?
  • Frequency definition
  • Units of measurement
• Light properties
• Light-related phenomena
• Colors
  • Origin
  • How we see them
• Lenses and mirrors
  • Definitions