Aim: What properties define wave classes? HW: Problem Set

Review Last time we talked about two kinds of waves and looked at the electromagnetic spectrum… Describe the two types of waves? On the EM spectrum, how does the frequency and wavelength vary across the spectrum? How do you draw a wave?

Two Classes of Waves Transverse Waves Longitudinal Waves The particles vibrate in a direction that is perpendicular to the waves propagation (direction of travel) The particles vibrate in a direction that is parallel to the waves propagation

Direction of wave travel is PERPENDICULAR to the motion of the medium Transverse Waves Direction of wave travel is PERPENDICULAR to the motion of the medium Particles: ↕ Energy: ↔ Example: Light Waves

Transverse Waves WAVELENGTH – the distance from one crest to another AMPLITUDE – the amount that a wave rises or falls Tells how much ENERGY the wave contains CREST OR PEAK – the highest point on a wave TROUGH – the lowest point on a wave

Direction of wave travel is PARALLEL to the Longitudinal Waves Direction of wave travel is PARALLEL to the motion of the medium Particles: ↔ Energy: ↔ Example: Sound waves Speed of Sound: 3.31 x 102 m/s

Longitudinal Waves WAVELENGTH – the distance from one compression to another COMPRESSION – area where particles in the medium are densely populated RAREFACTION – area where particles in the medium are sparsely populated AMPLITUDE – the size of a compression The ENERGY contained in the wave

Envelope Activity There are two situations regarding waves. Answer all the questions with your group.

1. The frequency of a sound wave from a pipe organ is 264 Hz 1. The frequency of a sound wave from a pipe organ is 264 Hz. List and draw everything about this wave (speed, wavelength, wave type, class). 2. A light wave with a wavelength of 619 nm travels across the classroom. List and draw everything about this wave (Speed, frequency, wave type, class, COLOR). 3. Sound waves are longitudinal waves. Why is the sound from a speaker louder when you sit closer to it? (In other words has more energy).

Question 3 Sound waves are longitudinal waves. Why is the sound from a speaker louder when you sit closer to it? (In other words has more energy). Because the amplitude of the sound wave gets smaller the farther it gets from its source. Sitting closer delivers more energy because the amplitude of the sound wave is greater!

Wave Transmission Transverse Waves (Light) Longitudinal Waves (Sound) DO NOT REQUIRE A MEDIUM Sparse to Dense (air to water) – SLOW DOWN Dense to Sparse (water to air) – SPEED UP Longitudinal Waves (Sound) MUST HAVE A MEDIUM Sparse to Dense – SPEED UP Dense to Spare – SLOW DOWN

Phase To be IN PHASE, two points on a wave must be traveling in the same DIRECTION and have the same DISPLACEMENT from EQUILIBRIUM “In Phase” = 0° or 360° “Out of Phase” = 180° Which points are in phase?

Phase The relative position between… Two similar points on different waves Pick the same point on each wave and look at the difference between their relative positions 360o out of phase, AKA IN PHASE 1 full wavelength apart 180o out of phase, 1/2 wave apart 90o out of phase, 1/4 wave apart 270o out of phase, 3/4 wave apart

Fundamentals Review Answer the following questions regarding wave fundamentals with either a written response or calculation.

Fundamental 1 A sound wave travels from air into metal, then from metal into water. What happens to the speed of the wave? Speeds up when going from air to metal. Slows down when going from metal to water.

Fundamental 2 Determine the frequency of a wave with a wavelength of 500 meters if it travels at a velocity of 25 meters per second. What is its period? v = fλ 25 m/s = f (500 m) f = 0.05 Hz T = 1 / f T = 1 / 0.05 Hz T = 20 s

Summary What is the difference between longitudinal and transverse waves? What is an example of both transverse and longitudinal waves? When does light slow down? When does sound speed up?