Waves Notes PDF

Classifying Waves Waves can be either electromagnetic or mechanical. ○​ Electromagnetic waves: ○​ waves capable of transferring energy through a vacuum. ​ e.g. Light waves ○​ Mechanical waves: ○​ waves that can only travel through a medium. ○​ M...

Classifying Waves Waves can be either electromagnetic or mechanical. ○​ Electromagnetic waves: ○​ waves capable of transferring energy through a vacuum. ​ e.g. Light waves ○​ Mechanical waves: ○​ waves that can only travel through a medium. ○​ Medium: ○​ matter through which a wave travels through; can be solid, liquid or gas. ​ e.g. Sound waves, water waves Waves can be either transverse or longitudinal. ​ Transverse: ○​ matter in the medium moves back and forth at right angles to the direction the wave is traveling. ​ Particle motion is perpendicular to wave motion. ​ e.g. Electromagnetic waves (light), vibrations in string instruments, ripples on water surface. ​ Crest ○​ The highest point in the wave ​ Trough ○​ Lowest point in the wave ​ Longitudinal (aka compressional waves): ○​ matter in the medium moves back and forth in the same direction that the wave is travelling. ​ Particle motion is parallel to wave motion.​ ​ e.g. Sound waves, ultrasounds, waves made with a slinky. ​ Compression: ○​ where particles are pushed together in a longitudinal wave. ​ Rarefaction: ○​ where particles are spread apart in a longitudinal wave. ​ Amplitude: ○​ the amount of energy carried by a wave ​ Transverse Waves (Height of the wave) ​ Longitudinal Waves (Amount of compression in the wave) ​ Wavelength (λ): ○​ the distance of one single wave. ​ Measured in m ​ Transverse Waves (Crest ↔ crest, trough ↔ trough, or resting point ↔ resting point) ​ Longitudinal Waves (Compression ↔ compression, or rarefaction ↔ rarefaction) ​ Period (T): ○​ the amount of time it takes one wavelength to pass a point. ​ Measured in s ​ Frequency (𝑓): ○​ the number of waves that pass a given point in one second. ​ Measured in Hertz (Hz) ​ 1 Hertz = 1/s or 1s-1 The higher the frequency, the shorter the wavelength. The lower the frequency, the longer the wavelength. ​ Wave speed (v): ○​ how fast the wave travels. ​ Measured in m/s ​ Speed is dependent on the type of wave and the properties of the medium the wave is traveling through. ​ Mechanical waves (sound) ○​ must travel through particles, therefore travel fastest through solids, then liquids, then gases, due to the closeness of particles. ​ Also travel through warmer mediums, because particles collide more. ​ Electromagnetic waves (light) ○​ do not need a medium, therefore travel fastest through a vacuum, and slowest through solids. ​ Wave Speed ○​ Wave Behavior ​ Reflection: when a wave strikes an object and bounces off of it. ○​ All types of waves can be reflected. ​ e.g. Echoes are reflected as sound waves. ​ Law of Reflection: ○​ angle of incidence is always equal to angle of reflection. ​ Refraction: ○​ the bending of waves caused by a change in its speed as it moves from one medium through another. ​ The greater the change in speed, the more the wave bends. How do prisms work? ​ Light waves enter into a prism and slow down due to the change in medium. ○​ This causes the waves to bend (refract) as they move through the new medium. ​ The different colours of light bend different amounts, thus the colours are separated. ​ This is because each colour of light is a different wavelength, so it travels at different speeds.  ​ Law of Reflection: ○​ angle of incidence is always equal to angle of reflection. ​ Diffraction: ○​ when an object causes a wave to change direction and bend around it. ​ Amount of diffraction depends on: ​ Size of object the waves hit. ​ Wavelength of waves. ○​ Sound waves tend to diffract much better than light waves because they are much larger. ​ Absorption: ○​ when a wave strikes an object and is absorbed by it. ​ Energy from the wave gets converted into thermal energy. ​ Dark colours are better at absorbing light waves than light colours, thus it is better to wear dark colours in winter to stay warmer. ​ Interference: ○​ when two or more waves combine to form a new wave. Constructive Interference Destructive Interference ​ when two or more waves add ​ when two or more waves subtract together. from one another when they ​ Like parts of a wave must line up. overlap. ​ Results in increased amplitude of ​ Opposite parts of a wave must line a wave. up. ​ Standing waves ○​ special type of wave pattern that forms when waves equal in wavelength and amplitude, but traveling in opposite directions, continuously interfere with each other. ​ Occurs when medium vibrates at a specific frequency. ​ Creates a wave that does not move or have a change in amplitude. ​ Resonance ○​ process where an object is made to vibrate at its natural frequency by absorbing the energy of another object that is vibrating at the same frequency. ​ Tuning forks of the same pitch. Electromagnetic Spectrum ​ Electromagnetic Waves ○​ electric and magnetic waves are released by a vibrating electric charge, capable of transferring energy through a vacuum. (no medium) ​ Instead of transferring energy from particle to particle, like mechanical waves, they transfer energy between electric and magnetic fields, which can exist with or without matter. ○​ All electromagnetic waves travel at a speed of 300,000,000 m/s in a vacuum. Slows down as they travel through matter. Electromagnetic waves can behave as waves and as particles, called photons. Waves Particles Photon a disturbance that can pieces/fragments of matter Massless bundles of carry energy energy ​ Electromagnetic waves give off energy in the form of electromagnetic radiation. ​ Electromagnetic spectrum ○​ the entire range of frequencies of electromagnetic radiation Shorter wavelengths mean higher frequency and higher energy. Longer wavelengths mean lower frequency and lower energy. Radio Waves Microwaves Infrared Waves Emitted by radio stations, Used for cooking, doppler Used in night vision MRIs, radar, Wi-Fi, TV, cell radar, GPS goggles, remote controls, phones infrared photography Longest wavelength with lower frequency Visible Light Waves Ultraviolet Waves X-Rays The only EM waves that Given off by the sun Used to take pictures of can be seen, given off by bones to check for the sun and light bulbs. used in lamps to kill breaks/fractures, CT scans bacteria Different colours of light Small enough to penetrate have different needed for the human skin cells wavelengths. body to make vitamin D. Overexposure can cause ROYGBIV: acronym to cancer remember order of colours - red is longest and violet is shortest. Gamma Rays Used to kill cancer cells in radiotherapy, sterilize  medical equipment, used in radioactive tracers Smallest wavelength with the highest frequencies Doppler Effect and Seeing ​ Doppler Effect ○​ change in frequency (and thus pitch) due to a moving wave source ​ Frequency ○​ Increases as source moves towards an observer and decreases as the source movies away from the observer ​ Source of wave must be moving with respect to the observer ○​ Used by astronomers to understand moving stars ○​ Most often experienced in life with sound waves As the fire truck moves towards the people: Waves are compressed, Shorter λ, Higher f, Higher pitch As the firetruck moves away from the people: Waves are more spread apart, Longer λ, lower f, Lower pitch ​ Seeing ○​ When light hits an object, the object absorbs most of the light and reflects the rest ​ Whatever colour is reflected hits the retina in your eye, such that you see the reflected colour. ​ 2 Parts of the retina that help you see: ○​ Rods ​ Work at low levels of light, used mainly at night ○​ Cones ​ Work at bright light levels, allow us to see colour ​ Lenses are used to redirect light waves and correct vision ​ Convex Lenses (aka Converging Lens) ○​ Thicker at middle than ends ○​ Bend light inwards to a single focal point ○​ Used to correct far-sightedness and for magnification ​ E.g. Reading glass, magnifying glass, rearview mirror ​ Concave Lenses (aka Diverging Lens) ○​ Thicker at the ends ○​ Bend all light outwards ○​ Used to correct near-sightedness ​ E.g Projector, make-up mirror, dental mirror