Waves and Lenses Pg. 92-116

What is a WAVE Wave: disturbance that travels through a medium (water, air, ground…) Transports energy It does NOT transport matter Ripples are the result of a disturbance that spreads across the surface of the water Picture a duck sitting in waves, the duck rises and falls but never moves Fig 4.2

Wave Characteristics Propagates (spreads) in two ways: transverse and longitudinal Transverse: its medium moves perpendicular to its motion Fig 4.3 Wave moves from left to right, but medium moves up and down

Wave Vocab Highest point of wave: Crest Lowest point of wave: Trough Transverse waves are made up of Crests and Troughs

Longitudinal Wave Medium moves parallel to the motion of the medium When a longitudinal wave propagates through a medium, its particles move closer together and then farther apart BUT always parallel to the direction of the wave’s motion Compression: region where particles are close together Rarefaction: region where particles are farther apart Fig 4.5 and 4.6

Amplitude Amplitude (A) of a wave: Depends on the energy transmitted by a wave The greater the energy transmitted, the greater the amplitude (when you make a rope make waves, the higher the waves the more energy you must put in) A: maximum distance travelled by a particle in the medium compared to its position at equilibrium Frequency of a wave connects with the Pitch of a sound

Amplitude cont. Transverse waves Amplitude: max. height of crest or max. depth of trough, from the position at equilibrium Fig 4.8 Longitudinal waves Amplitude: harder to measure. Depends on density of compression The denser the region of Compression , the greater the Amplitude Fig 4.9 Amplitude= Loudness of the sound

Wavelength ‘Lambda’ (λ) Is the length of a wave’s complete cycle Transverse wavelength: distance between 2 consecutive crests or troughs Longitudinal wavelength: length of 1 compression and 1 rarefaction Fig 4.10 and 4.11 (copy in notes)

Frequency Frequency: number of cycles per unit of time Measured in Hertz (Hz) If a wave has a frequency of 1Hz, it completes one full cycle in one second Speed= frequency x wavelength

Types of Waves 2 types of waves: Mechanical Electromagnetic Mechanical wave: a wave that requires a medium (solid, liquid or gas) in order to propagate (spread out) Ex: water is the medium for water waves, air is medium for sound waves, ground is medium for seismic waves during earthquake

Types of Waves cont. Did you know that there is no sound in space….but our movies would be boring without this, so movie makers ignore this fact to make it more interesting for the viewer!! Electromagnetic wave: is a wave that can travel in both vacuum and a medium Ex: light waves (transverse waves) that move just as easily in a vacuum as a medium – Sun rays reach us through interstellar space and the atmosphere Electromagnetic waves carry energy from point to another Form of energy is radiant waves

Types of waves cont. Electromagnetic waves ex: radio waves, light waves, ultraviolet waves, X-rays…

Pg. 98-99 Create a table in your notes using these pages Title Description 1 example you choose 1 example related to health care

Sound Waves Sound: longitudinal mechanical wave Produced by vibration of an object Transmitted to the object’s environment Ex: chair falls to floor, its impact causes particles in floor to vibrate, these disturbances are passed on to the surrounding medium (ex: air) the wave produced transmits sound energy

The Decibel Scale Sound can be soft like a whisper or loud like a scream Volume depends on intensity or energy is it transmitting The greater the energy the greater the sound Less energy = less amplitude = less sound Intensity of sound is measured in Decibels (dB)

Decibel (dB) Not an exact scale, relative to perception by the human ear Decibels are measured in 10s, so when something is increased by 10 dB, it becomes 10 times louder Sound measuring 40dB is 100 times louder than a 20dB sound Decibels are not cumulative (two separate 50dB do not make 100 dB)

Dangerous Decibel levels Fig 4.20 Prolonged exposure to sounds louder than 100 dB can cause long-term hearing damage Starting at 120 dB pain and immediate hearing loss can ensue (ear protection needed)

Light Waves pg. 106 Light is an electromagnetic wave that is visible to the human eye Ex: light bulb, sun, fire Light waves travel in straight lines AKA light rays Light waves can be reflected or refracted when they strike an object

Reflection Reflection: rebounding of light that occurs when a light ray hits a different medium and ‘bounces back’ to the original medium Ex light rays passing through air and rebounding off of a mirror If we can see an object it is because reflection brings light to our eyes Fig 4.26 copy this diagram into your books and label the lines

Reflection cont. Incident ray: ray that contacts the surface of an object Reflected ray: ray that rebounds Normal: is a line perpendicular to the surface at the point of reflection Angle of incidence: angle formed by the incident ray and the normal Angle of reflection: angle formed by the reflected ray and the normal

Reflection cont. Reflection: Diffuse reflection Specular reflection Diffuse reflection: most objects have rough surfaces (paper or balloon), when parallel lines hit the uneven surface they reflect in all directions (light rays do not respect the laws of reflection)

Reflection cont. Specular reflection: light contacts a perfectly smooth surface (ex: mirror), rays follow laws of reflection When parallel light rays contact a smooth surface their reflection is parallel Producing a true mirror image

Reflected image Image appears to be behind the mirror at the same distance as the reflected object AKA Virtual Image (made by the prolongation of reflected rays) not the real rays!! Real Image is made by real crossing of light rays Image is the same size as object Image is horizontally inverted (the left is now the right side)

Reflected Image pg. 109 Can localize Virtual image beyond plane of mirror by drawing incident rays from the object and the resulting rays Image produced at the meeting point of the prolongation of the reflected rays Fig 4.31

Plane mirrors Change the trajectory of light rays by reflection Increase the observer’s field of vision Think of a review mirror on a car, or the mirror your dentist uses They change the trajectory of light rays so the rays can reach the eye of the observer

Refraction Refraction: the deviation of light ray as it passes from one transparent medium to another (ex: air to water) Fig. 4.33 take a look! Lenses help to refract light as it passes through them

Lenses Lenses: 2 types of lenses: objects made up of transparent materials have at least one curved surface ability to refract light as it passes through them 2 types of lenses: Converging Diverging

Focal points There are 2 focal points between diverging and converging lenses Principal Focal Point (F) Secondary Principal Focal Point (F1) Pg 112 look at the images

Converging Lens

Converging lens Focal point of converging lens real point where the refracted rays actually meet when the incident rays run parallel Ex: magnifying glass

Diverging Lens

Diverging lens Focal point of diverging lens is the virtual point from which the refracted light rays appear to emanate when the incident rays run parallel

Applying what you know… Pg. 114 image has many outcomes, lets look at them all... Pg. 115 image is virtual and smaller than object