Waves Unit 4 Ch 8 MHR

Introduction A wave is a disturbance that transfers energy through a medium. A medium is a material through which a wave travels e.g. air, liquid, solid Two types of waves: mechanical and electromagnetic (EM)

Introduction Periodic motion refers to a repeated pattern of motion over a regular time interval e.g. simple pendulum, rotating planet, water waves, metronome. A cycle, vibration, or oscillation is one complete repetition of the pattern. The period is the time required for one complete cycle.

Introduction The rest or equilibrium position is the initial position of the object e.g. pendulum hanging freely. The amplitude is the maximum displacement from the rest position

Introduction The frequency is the number of cycles completed in a specific time interval. The unit for frequency is the hertz (Hz) or cycle/s. a cycle is just a physical count so 2 Hz * 3 m = 6 m/s T = t/N where t = total time & N = cycles f = N/t so T = 1/f (reciprocals)

Period and frequency Example a simple pendulum makes 3 cycles in 10. s, what is the period and the frequency? T= 10.s/ 3 cycles = 3.3 s f = 3 cycles/10. s = 0.30 Hz

Wave Terminology Crests are high or maximum points Troughs are low or minimum points The wavelength is the distance from crest to adjacent crest or trough to adjacent trough

Classifying waves by direction of travel and displacement of media Waves can either be transverse or longitudinal. Transverse waves are those in which the displacement of the particles of the medium is perpendicular to the direction of travel or propagation of the wave e.g. a sideways pulse in a slinky,

Classifying waves by direction of travel and displacement of media A longitudinal wave is one in which the displacement of the particles of the medium is parallel to the direction of travel of the wave e.g. a sound wave. See your text.

Wave behaviour at boundaries The speed of a wave in a material medium depends on properties of the medium. If a wave pulse is generated in both a heavy spring and a light spring, the pulse travels faster in the light spring. Think about why this occurs.

Wave behaviour at boundaries If two long springs are joined together each of substantially different force constants e.g. one is a heavy spring and the other is light, we notice that when a series of pulses are generated and travel down the spring, there is a speed and size change at the boundary. Note here that the frequency with which the pulses are generated does not change.

Wave behaviour at boundaries When a wave travels from a less dense (lighter) medium to a more dense (heavier) medium, the speed decreases and the wavelength decreases. When a wave travels from a more dense (heavier) medium to a less dense (lighter) medium, the speed increases and the wavelength increases.

Reflection and Transmission When a wave reaches a boundary between two springs of different force constants, some of the wave is reflected and some is transmitted. If a wave travels from a less dense to a more dense medium, the transmitted wave has the same orientation as the initial wave, but the reflected wave is inverted.

Reflection and Transmission If a wave travels from a more dense to a less dense medium, then the reflected and the transmitted waves are on the same side of the spring or rope. See text p. 351