1. Physics 11 An Introduction to Waves and Sound

2. Definition of a Wave
Waves: a disturbance or vibration that transfers energy progressively from point to point in a medium.

3. Types of Waves
Mechanical Waves: require a material medium. (Ex. Water waves, sound waves, waves in springs or ropes)
Electromagnetic Waves: require no material medium. (Ex. Light waves, radio waves and x-rays)
Matter Waves: Particles of matter “wave” when moving. (Quantum mechanics is needed to describe these waves. Electrons and other particles show wave-like behavior under certain circumstances)

4. Mechanical Waves two main types of mechanical waves. Transverse Waves
Wave (Energy) Movement
Crest/Peak
Particle Movement
Valley/Trough

5. Types of Mechanical Waves
Transverse Waves
Click here to view a propagating transverse wave.
Key Features:
Particles move UP and DOWN
Wave energy propagates (moves) forward at a very specific speed.
The wave speed is dependent on the type of material (or medium) that the wave is traveling through not on the amount of energy or amplitude (size) of the wave.

6. Types of Mechanical Waves
Transverse Waves (The Wave)

7. Mechanical Waves Longitudinal Waves (Compression Waves)
Wave (Energy) Movement
Compression
Particle Movement
Rarefaction

8. Types of Mechanical Waves
Longitudinal Waves
Click here to view a propagating longitudinal wave.
Key Features:
Particles move SIDE to SIDE
Wave energy propagates (moves) forward at a very specific speed.
The wave speed is dependent on the type of material (or medium) that the wave is traveling through not on the amount of energy or amplitude (size) of the wave.

9. Speed of Waves Heavy medium  slower speed
Speed of wave is dependent on the properties of the medium through which it is travelling.
Heavy medium  slower speed
Lighter medium  faster speed
Increased tension  faster speed
Amplitude  does not affect speed
No real difference in speeds between Transverse and Longitudinal wave

10. Waves At Boundaries Between Media
Waves can move (transfer) from one Medium into another medium.
What happens to the energy as the wave passes from one medium into another medium? What happens to the speed and size of the wave?

11. Transmission and Reflection
Two things happen when a wave reaches a boundary
1. Part of the energy is transmitted into
the medium (Transmitted Wave)
2. Part of the energy moves backward
from the boundary (Reflected Wave)

12. Waves at Boundaries…continued
When the medium changes, wave energy is both reflected and transmitted.
Two Cases:
1. Difference in media is small: most of the energy will transmit.
2. If the two media are very different: most of the energy will be reflected.

13. Important Question Is the reflected wave INVERTED or ERECT?
Whenever a wave passes from a less dense to a more
dense medium, the reflected wave is inverted.
When a wave passes from a more dense to a less dense
medium, the reflected pulse is erect, not inverted.

14. Superposition of Waves
Principle of Superposition:
“The displacement of a medium caused by two or more waves
is the algebraic sum of the displacements caused by the
individual waves.” Physics: Principles and Problems, Merrill, 1992

15. Interference
When two or more waves interact with one another it is called interference.
There are two types of interference:
CONSTRUCTIVE INTERFERENCE: When wave displacements are in the same direction the result is a wave that has a larger amplitude than either of the original waves.
Click Here!
DESTRUCTIVE INTERFERENCE: If the wave displacements are in opposite directions the result is a wave with a smaller amplitude
Than the individual waves.
Click Here!

16. References Animated waves are compliments of:
Dr. Dan Russel of Kettering University – Applied Physics