1.1 understanding waves

Chapter 4 WAVES

1.1 UNDERSTANDING WAVES

A student is able to• describe what is meant by wave motion;• recognise that waves transfer energy

without transferring matter;• compare transverse and longitudinal waves

and give examples of each;• state what is meant by a wavefront;• state the direction of propagation of waves

in relation to wavefronts.

1.1 UNDERSTANDING WAVES

Waves• A wave is a travelling DISTURBANCE

from a vibrating or oscillating source.

1.1 UNDERSTANDING WAVES

Waves• A wave carries energy along with it in

the direction of its propagation.• A wave is a mean of energy transfer

through vibration.

1.1 UNDERSTANDING WAVES

Example of Waves• Light waves - produced as a result of

vibrations of electrons in an atom • Sound waves - produced by vibrating

mechanical bodies such as a guitar strings or a tuning fork

• Water waves - produced by a disturbance on a still water surface

1.1 UNDERSTANDING WAVES

Wave motion• The transfer of energy through

space without the accompanying transfer of matter.

1.1 UNDERSTANDING WAVES

How do wave transfer energy?1.1 UNDERSTANDING WAVES

• When the string is shaken up and down, a disturbance moves along the length of the string. • It is the disturbance that

moves along the length of the string, not parts of the string itself.

How do wave transfer energy?1.1 UNDERSTANDING WAVES

• When energy is transferred by a wave from a vibrating source to a distant receiver, there is no transfer of matter between the two points.

How do wave transfer energy?1.1 UNDERSTANDING WAVES

• Drop a stone in a quiet pond. It will produce a wave that moves out from the center in expanding circles. It is the disturbance that moves, not the water. After the disturbance passes, the water is where it was before the wave was produced .

How do wave transfer energy?1.1 UNDERSTANDING WAVES

• From the two examples, the string and water is the medium through which wave energy travels.

1.1 UNDERSTANDING WAVES

Types of waves1.1 UNDERSTANDING WAVES

Transverse waveA transverse wave is a wave in which the vibration of particles in the medium is at right angle (perpendicular) to the direction of propagation of the wave. Eg: water waves, light waves

1.1 UNDERSTANDING WAVES

Longitudinal waveA longitudinal wave is a wave which the vibration of particles in the medium is along (parallel to) the direction of propagation of the wave.Eg: Sound waves

1.1 UNDERSTANDING WAVES

WavefrontA wavefront is a line or plane on which the vibrations of every point on it are in phase and are at the same distance from the source of the wave.

1.1 UNDERSTANDING WAVES

Wavefront1.1 UNDERSTANDING WAVES

1.1 UNDERSTANDING WAVESWavefront

1.1 UNDERSTANDING WAVESExample

1.1 UNDERSTANDING WAVESExample

1.1 UNDERSTANDING WAVESDisplacement – Distance graph for Waves

https://www.youtube.com/watch?v=P-Umre5Np_0

1.1 UNDERSTANDING WAVESAmplitude

The maximum displacement from equilibrium of an element of the medium is called the amplitude A of the wave.

Displacement

1.1 UNDERSTANDING WAVESWavelength, λ

1.1 UNDERSTANDING WAVESWavelength, λ

The distance between two adjacent points of the same phase on a wave. Eg: Distance from crest to crest (trough to trough)

1.1 UNDERSTANDING WAVESWavelength, λ

The distance between two successive compressions or two successive rarefactions in a sound wave.

Compression Rarefaction

1.1 UNDERSTANDING WAVESPeriod, T

• The time taken for an oscillation to complete ONE cycle.

• SI unit is second (s).

1.1 UNDERSTANDING WAVESFrequency, f

• The number of waves (oscillations) produced in ONE second.

• SI unit is Hertz (Hz)

Tf 1

1.1 UNDERSTANDING WAVESExample 1

From the graph, calculate:a. Amplitude b. Period c. Frequency

1.1 UNDERSTANDING WAVESExample 2

1.1 UNDERSTANDING WAVESExample 2

1.1 UNDERSTANDING WAVESExample 3

1.1 UNDERSTANDING WAVESExample 4

1.1 UNDERSTANDING WAVESExample 5

1.1 UNDERSTANDING WAVESDisplacement-Time graph

1.1 UNDERSTANDING WAVESDisplacement-Distance graph

1.1 UNDERSTANDING WAVESWave speed, v• The speed of a wave is the measurement of

how fast a crest is moving from a fixed point.• SI unit is [m s-1]

1.1 UNDERSTANDING WAVESThe relationship between speed, wavelength and frequency

Eg:A wave of frequency 120 Hz has a wavelength of 5.0 m. What is the speed of the wave?

Velocity = wavelength x frequencyv = f λ

1-

1

s m 6000.5120

m 0.5s m 120

fv

f

1.1 UNDERSTANDING WAVESExample 6

1.1 UNDERSTANDING WAVESDamping

1.1 UNDERSTANDING WAVESWhat is damping?• Damping is the decrease in the

amplitude of an oscillating system when its energy is drained out as heat energy.

• The amplitude of an oscillating system will gradually decrease and become ZERO when the oscillation stops.

• But, frequency does not change.

1.1 UNDERSTANDING WAVESWhat causes damping?• External damping of the system is the

loss of energy to overcome frictional forces or air resistance.

• Internal damping is the loss of energy due to the extension and compression of the molecules in the system.

1.1 UNDERSTANDING WAVESA graph to show damping.

1.1 UNDERSTANDING WAVESExample 4

1.1 UNDERSTANDING WAVES• To enable an oscillating system to go on

continuously, an external force must be supplied to the system.

• The external force supplies energy to the system. Such a motion is called a forced oscillation.

• The frequency of a system which oscillates freely without the action of an external force is called the natural frequency.

1.1 UNDERSTANDING WAVESResonance• Resonance occurs when a system is made

to oscillate at a frequency equivalent to its natural frequency by an external force.

• The resonating system oscillates at its maximum amplitude.

1.1 UNDERSTANDING WAVESResonanceBarton Pendulum Experiment

1.1 UNDERSTANDING WAVESResonance

Breaking glass using resonancehttps://www.youtube.com/watch?v=17tqXgvCN0E

Tacoma bridgehttps://www.youtube.com/watch?v=3mclp9QmCGs

Barton Pendulum Experimenthttp://cikguwong.blogspot.my/2011/01/physics-form-5-chapter-1-bartons.html