Waves Waves

What are waves? A wave is a phenomenon in which

energy is transferred through vibration.

Types of Waves Transverse Waves

Longitudinal Waves

Transverse Waves are waves which travel in a direction

perpendicular to the direction of vibrations.

Direction of vibrations

Direction of wave

Generating Transverse Waves

Transverse Wavesexamples include

water wavesrope waveslight waveelectromagnetic waves

Longitudinal Waves

are waves which travel in a direction parallel to the direction of vibrations.

Direction of vibration

Direction of wave

examples include

sound wavessound waves

Generating of Longitudinal Waves [slinky spring]

Characteristics of A Wave Crests and Troughs Amplitude Wavelength Frequency Period Speed

Crests and Trough Crests are high point of a wave Troughs are low point of a wave

displacement

distance

crest crest

troughtrough

Amplitude (A) is the height of a crest or depth of a

trough measured from the normal undisturbed positions.

displacement

distance

crest crest

trough

Amplitude

Amplitude

SI Unit For Amplitude is measured in metres (m)

displacement

distance

crestcrest crestcrest

trough

Amplitude

Amplitude

Wavelength () is the distance between two

successive crests or troughsdisplacement

distance

Amplitude

AmplitudeAmplitude

crestcrest crest

trough trough

Wavelength

Wavelength

SI Unit For Wavelength is measured in metres (m)

displacement

distance

Amplitude

Amplitude

crestt crest

trough trough

Wavelength

Frequency (f) is the number of vibrations in one

second.

SI Unit For Frequency is the Hertz (Hz)

1 Hz is 1 vibration in 1 second.

50 Hz is 50 vibrations in 1 second.

Test Yourselves Explain the meaning of

28 Hz, 100 Hz , 135 Hz, 1570 Hz.

Period (T) is the time taken for one complete

vibration. (or oscillation or cycle)

SI Unit For Period is measured in second (s)

Relationship between Period (T) and Frequency (f)

f = 100 Hz T = 1/100 s f = 40 Hz T = 1/40 s f = 23 Hz T = 1/23 s f = 8 Hz T = 1/8 s f = f Hz T = 1/f s

Relationship Between f and T

f1T

Speed Of a Wave

is the distance moved in one second.

SI Unit For Speed is measured in metre per second (ms-1or m/s)

Wave Equation Speed of a wave

= wavelength period= wavelength x frequency

where v = speed, f = frequency and = wavelengthV = f

Describing WavesDisplacement-Time Graph

for one particle on the wave

timetime

displacementdisplacement

GCE O-LevelGCE O-Level Past Examination PaperPast Examination Paper

Science (Physics)

Nov 1991

9. The diagram shows the outline of a water wave.What are the values of the amplitude and the wavelength?

amplitude / cm wavelength / cm

A 0.6 10 B 0.6 20 C 0.6 30 D 1.2 20

B

GCE O Nov 1994

11. Which wave is longitudinal ?

A lightB radioC soundD water

C

D

O’ level Physics Nov 1995

11. The speed of 100 Hz wave was measured on four different days. The results are shown in the table. On which day the wave have the longest wavelength ?

day speed of wave

A 315 ms-1

B 320 ms-1

C 335 ms-1

D 340 ms-1

GCE O Nov 1996

9. A source vibrates at frequency of 20 Hz and produces waves of wavelength 0.02 m.

At which speed do these waves travel out from the source ?

A 0.001 ms-1 B 0.021 ms-1 C 0.40 ms-1 D 20 ms-1 C

Hint:

v = f

Nov 1998

9. A VHF radio station broadcasts at a frequency of 60MHz (6.0 x 107 Hz). The speed of radio waves is 3.0 x 108ms-1.What is the wavelength of the waves broadcast by the station?

A 0.2 mB 0.5 mC 2.0 mD 5.0 m D

Hint:v = f

Nov 1998

5. The diagram shows a coil spring along which a longitudinal wave is moving.(a) Mark on the diagram a distance equal to the wave length of the wave. [1]

(b) Label on the diagram with the letter C where the coils of the spring are compressed. [1]

Wave length

C

(continue in next slide)

C C

(c) Is the wave on the spring more like a sound wave or a light wave? [1]

Nov 1998(Cont. …) Q 5

Sound wave, because sound wave is a longitudinalwave but light wave is a transverse wave..

Nov 1997

5. The diagram below shows a transverse wave travelling a rope.

(a) Mark on the diagram which is equal to (i) the wavelength, (ii) the amplitude of the wave. Label your answers. [2] (b) If the wavelength is 0.8m and the frequency is 2 Hz, what is the speed at which the wave moves along the rope ? [2]

wavelength

amplitude

v = f = 0.8 x 2 = 1.6 ms-1

Nov 1996

6(a) Explain the difference between a transverse and a longitudinal wave. [2]

(b) State one example of each type of wave.TransverseLongitudinal [2]

Light Sound

Transverse wave is a wave that its direction of vibration is perpendicular to the direction of propagation. It can travel through vacuum. Longitudinal wave is a wave that its direction of vibration is parallel to the direction of propagation. It needs medium to travel.

9.(a) Explain the difference between transverse and longitudinal waves, referring in your answer to

the direction in which the waves travel. [2]

GCE ‘O’ LEVEL Nov 1995

Transverse waves are waves that their directionof vibration is perpendicular to their directionof propagation. Longitudinal waves are waves that theirdirection of vibration is parallel to theirdirection of propagation.

(continue on next slide)

9.(b) The speed of sound in water is 1500m/s. What is a wave length of a sound wave of frequency 250Hz travelling through water ? [2]

Since v = ftherefore 1500 = 250 = 1500 / 250 = 6.0 m

(Cont. …) Q. 9 Nov 1995

Nov 1993

6. The diagram shows the air pressure at different distances from a loudspeaker.

(continue on next slide)

(a) Mark carefully on the diagram: [2] (i) a distance which is the wavelength of the sound wave; (ii) the amplitude of the sound waves.

wavelength

amplitude

6(b) If the wavelength of a sound wave of frequency 250 Hz is 1.4 m, calculate the speed of the wave. [2]

(Cont. …) Q. 6 Nov 1993

since v = ftherefore, = 1.4 x 250 = 350 ms-1

5.(a) With the aid of a diagram, explain what is meant by the frequency and wavelength of a wave. [5]

GCE O Nov 1990

(b) What is a longitudinal wave ? [2]

Frequency is thenumber of vibrationsper second.Wavelength is the distance from a point on a wave to its next corresponding point.It usually denote as ..

Longitudinal wave is a wave that its directionof vibration always parallel to the direction ofpropagation.

(continue in next slide)