4/30/10

Post date: Apr 29, 2010 5:20:9 PM

Bell Activity: What is a wave?

    • "The Wave"

      • Students line up and do "the wave" (like at a stadium)

      • One person starts "the wave" - this initial event is called a disturbance

      • The initial disturbance moves down the line of people; we say the disturbance propagates

        • Each person in line does what the last person did

        • Each person does their part after the person next to them does theirs.

      • There is some material that the wave travels through, we call it the medium (here the students were the medium)

      • How quickly the wave moves down the line of people is called the wave speed

    • Types of waves

      • Transverse waves - particles move perpendicular to the wave's motion (like we did earlier, where the wave moves down the line of people, but each person moves up and down)

        • Examples: waves on a spring, "the wave", light waves

      • Longitudinal waves - particle move parallel to the wave's motion

        • Examples: leaning wave, spring when you compress a section and let it go, sound waves

      • Wave pulse - one disturbance is sent down the line

      • Traveling wave - repeated disturbance is sent down the line

      • Standing wave - when the medium has a boundary at one end, the wave may be reflected in such a way as to make the wave look like it is standing still (click on the image below to see this)

    • Anatomy of a wave

      • Period (T) - the time for a particle's motion to repeat - measured in seconds

      • Frequency (f) - how many cycles occur in one second - measured in Hertz (hz)

      • Equilibrium - the resting position of the medium

      • Peak - the highest point on the wave

      • Trough - the lowest point on the wave

      • Wavelength (lambda) - distance between like points on the wave (e.g. peak-peak or trough-trough) - measured in meters

      • Velocity (v) - how quickly the wave moves down the line - measured in m/s

      • Amplitude (A) - a wave's maximum distance from equilibrium - measured in m

    • Equations

      • Frequency and Period

        • are the inverse of each other

        • f = 1/T

      • The wave equation

        • relates wave speed, frequency, and wavelength

        • v = f * wavelength

  • Page 304:1-6

      • Remember that v=d/t

      • The speed of light is approximately 3.00 x 10^8 m/s.

      • Answers:

        1. 10 m/sec

        2. 5.0 m/sec

        3. a) 29 cm/sec b) 0.21 sec

        4. a) 2.4 m/sec b) 2.9 m

        5. 6.0 x 10^-7 m

        6. 4.2 m/sec