Physics Waves 1 Waves The components of all

Physics Waves 1

Waves • The components of all waves include: • Wavelength • Amplitude • Frequency • Period • Velocity • Waves transfer energy over distances. An example would be heat from the Sun or an earthquake. No mass is being transferred, just energy. 2

Wavelength and Amplitude (λ) Wavelength Amplitude Crest Time Trough Also, one wavelength ( ) 3 http: //www. howlaserswork. org/light-physics/wavelength-frequency-and-amplitude/

Frequency • Frequency is the number of waves passing by a particular point in a given length of time. • The number of waves per second is measured in Hertz (Hz). http: //www. casellausa. com/en/images/help/sine_waves. jpg 4

Period and Speed • The period is the length of time it take for one wave to pass. • The speed of the wave can be calculated by: • Speed = Distance traveled by the wave Time of travel or • Speed = Wavelength x Frequency 5

Calculating Wave Speed If a boy blows his trumpet, how fast will the sound travel to his friends who are 170 meters away and who hear the sound 0. 5 seconds later? Speed = Distance / Time Speed = 170 m / 0. 5 s Speed = 340 m/s 6

Calculating Wave Speed If the wavelength of the wave generated in a slinky is 0. 5 m and the frequency of the wave is 7 Hz, what is the wave speed? Speed = Wavelength x Frequency Speed = 0. 5 m x 7 Hz Speed = 3. 5 m/s Hz = Hertz = waves/sec 7

Longitudinal vs. Transverse Waves Longitudinal Wave (Compression wave) Transverse Wave Slinky waves can be made by vibrating the first coil back and forth in either a horizontal or vertical direction. 8 http: //www. glenbrook. k 12. il. us/gbssci/phys/Class/waves/u 10 l 1 a. html

Longitudinal Waves Particle displacement is parallel to the direction of wave propagation. 9 http: //www. kettering. edu/~drussell/Demos/wavemotion. html

Sound Waves • Sound waves are longitudinal waves. • Sound waves must travel through a medium. There is no sound in a vacuum. • Sound waves vibrate the eardrum. • The vibrations pass through the middle ear bones to the cochlea. • In the cochlea, the vibrations bend tiny hairs which convert the sound waves to nerve impulses. 10 http: //www. glenbrook. k 12. il. us/GBSSCI/PHYS/Class/sound/u 11 l 2 d. html

Transverse Waves Particle displacement is perpendicular to the direction of wave propagation. http: //www. kettering. edu/~drussell/Demos/wavemotion. html 11

Light Waves • Light travels in transverse waves. • Light is composed of little packets of energy called photons, which do not need to travel through a medium. • Light can travel through a vacuum. • Visible light is the colors of the visible spectrum: Red, Orange, Yellow, Green, Blue, Indigo and Violet • A mnemonic device to remember the colors is ROY G BIV. • Visible light is only one portion of the electromagnetic spectrum of energy waves. 12

Electromagnetic Spectrum http: //www. lakeeriewx. com/Case. Studies/Radar. Sun. Spikes/EM_Spectrum 3 -new. jpg 15 13

Vision and Light Waves Vision involves two main components: o Focusing the light that enters the eye onto the retina. This is accomplished by the curved cornea and the lens. o Activation of the photoreceptors in the retina to transmit nerve impulses to the brain. The is carried out by the rods and cones. 14

Water Waves • Water waves involve a combination of both longitudinal and transverse motions • As a wave travels through the water, the particles travel in clockwise circles. 15 http: //paws. kettering. edu/~drussell/Demos/wavemotion. html

Seismic Waves • P waves are longitudinal. • S waves are transverse. • Surface waves are both longitudinal and transverse. • Tsunamis are water surface waves, therefore they are both longitudinal and transverse. 16

Waves and Matter • Waves are the transmission of energy. • When coming in contact with matter, waves undergo: o Reflection – bouncing back o Refraction – bending o Absorption – passing into the matter o Transmission – passing through the matter 17

Reflection of Waves • Reflected waves are simply those waves that are neither transmitted nor absorbed, but are bounced back from the surface of the medium they encounter. • When a wave approaches a reflecting surface, such as a mirror, the wave that strikes the surface is called the incident wave. The one that bounces back is called the reflected wave. • An imaginary line perpendicular to the point at which the incident wave strikes the reflecting surface is called the normal. 18

Normal http: //laser. physics. sunysb. edu/~amy/wise 2000/websites/Mirror 348. jpg 19

The Law of Reflection • Objects can be seen by either the light they emit or by the light they reflect. • Reflected light obeys the law of reflection, that the angle of incidence equals the angle of reflection. • The Law of Reflection also applies to water waves, sound waves, and billiard balls as well. Angle I = Angle R http: //www. glenbrook. k 12. il. us/gbssci/Phys/mmedia/optics/lr. html 20

Law of Refraction: Snell’s Law • Snell's law gives the relationship between angles of incidence and refraction when light passes from one transparent medium to another. • Light bends according to Snell's law which states: n 1 sin θ 1 = n 2 sin θ 2 n 1 θ 1 n 2 θ 2 = the refractive index of substance 1 = the angle of incidence in substance 1 = the refractive index of substance 2 = the angle of refraction in substance 2 21

Refraction Light twists inward when entering medium of higher index of refraction. Light twists outward when entering medium of lower index of refraction. 22 http: //sol. sci. uop. edu/~jfalward/refraction. html