Learning Objectives describe what is meant by wave motion as illustrated by vibration in ropes, springs and experiments using a ripple tank. state what is meant by the term wavefront. show understanding that waves transfer energy without transferring matter. define speed, frequency, wavelength, period and amplitude. recall and apply the relationship velocity = frequency x wavelength to new situations or to solve related problems. compare transverse and longitudinal waves and give suitable examples of each.
What Is a Wave? A wave may be thought of as a spreading of disturbance from one place to another. “Ripples.” As ripples spread out, they carry along with them, energy.
Wave Motion Common to ALL wave motion. Vibration or oscillation transfer of energyWave motion provides a mechanism for the transfer of energy from one point to another WITHOUT the physical transfer of the medium such as rope or water between two points.
Transverse Waves Travel in a direction perpendicular to the direction of vibration. Displacement of the particles is at right angles to the direction of travel of wave motion. Example: Transverse waves created by vertical swinging of a rope fixed at one end.
Transverse Waves Made up of crests and troughs. Example: rope waves, water waves, light waves and radio waves, infra red waves, etc.
Longitudinal Waves Travel in a direction parallel to the direction of vibration. Displacement of the particles is in line with or parallel to the direction of travel of wave motion. Example: Longitudinal waves created by horizontal motion of a spring fixed at one end.
Longitudinal Waves Made up of compressions and rarefactions. Example: sound waves.
Properties of Wave Motion Crests (high points) and troughs (low points) of transverse waves Amplitude A: maximum displacement from rest position in either direction. SI unit: metres(m)
Properties of Wave Motion Phase: Two points in phase move in the same direction with same speed and have same displacement from rest position (See red dot).
Properties of Wave Motion Wavelength: shortest distance between any two point on a wave that is in phase. SI unit: metres (m)
Properties of Wave Motion Frequency, f: number of complete waves produced per second. SI unit: hertz (Hz) Period, T: time taken to produce one complete wave. SI unit: second (s) T = 1/f T
Types of Graphs Displacement–distance graph: Wavelength measurement Displacement-Time graph: Period measurement
Properties of Wave Motion Wavefront: imaginary line on a wave that joins all points which have the same phase of vibration.
Wave Equation Wave speed, v: distance travelled by a wave in one second. SI unit: m/s. Speed = distance / time. V = / T. But f = 1 / T. v = f
Example 1 Figure shows waves moving on a slinky with frequency 3 Hz and a wavelength of 0.3 m. What is the wave speed? v = f v = 3(0.3) = 0.9 m/s
Example 2 Speed of green light,c, of wavelength 0.6µm in vacuum is m/s. What is its frequency? v = f Given: = 0.6µm = 6.0 x m, c = 3.0 x 10 8 m/s C = f f = c / = 3.0 x 10 8 / 6.0 x = 5.0 x Hz
The Ripple Tank Uses 1.Generating water waves 2.All the basic properties of waves, including reflection, refraction, interference and diffraction, can be demonstrated. Structure 1.Shallow glass-bottomed tray 2.Light source (lamp) above tray 3.White screen below tray: capture image of shadows formed as water waves traverse the tray
Wave Pattern in Ripple Tank Reflection of waves 1.No change in speed or wavelength 2.Angle of incidence = angle of reflection
Wave Pattern in Ripple Tank Effect on waves from DEEP to SHALLOW water 1.Wavelength of water waves becomes shorter in the shallow water. 2.Waves slow down as they reach the shallow region. 3.Frequency remains unchanged.
Wave Pattern in Ripple Tank Refraction of waves 1.When decrease in depth occurs at an angle to the incident waves, the waves change direction (refraction occurs). 2.Water waves slow down 3.Frequency remains unchanged.