Waves Nature

What are waves?

What are waves? A wave is a phenomenon in which energy is transferred through vibration.

What are mechanical waves? Mechanical waves are waves which require a medium. A medium is a form of matter through which the wave travels (such as water, air, glass, etc.) Waves such as light, x-rays, and other forms of radiation do not require a medium.

Type of Waves Transverse Waves In a transverse wave the matter in the wave moves up and down at a right angle to the direction of the wave. 5

Transverse Waves are waves which travel in a direction perpendicular to the direction of vibrations. Direction of vibrations Direction of wave

Longitudinal Waves (compression waves) In a longitudinal wave the matter in the wave moves back and forth parallel to the direction of the wave.

sound waves Longitudinal Waves (compression waves) are waves which travel in a direction parallel to the direction of vibrations. Direction of vibration Direction of wave sound waves examples include

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 crest distance trough

Check your understood Ans. A , E , I 1. Which points of crests ? displacement A I E B D F H distance O J C G Ans. A , E , I 1. Which points of crests ? 2. Which points of troughs ? Ans. C , G

Amplitude (A) is measured in metres (m) is the height of a crest or depth of a trough measured from the normal undisturbed positions. is measured in metres (m) displacement distance crest trough Amplitude Amplitude

Wavelength () is measured in metres (m) is the distance between two successive crests or troughs displacement distance crest trough Wavelength Wavelength is measured in metres (m)

Transverse waves Longitudinal waves wavelength 14

symbols of wavelength = 15

Check your knowledge displacement A I E B D F H distance O J C G Which pairs points are called wavelength? (true or false) A ->C , B -> E , A -> E , D -> F , B -> F

f = symbols of frequency = f n = number of wave , t = time frequency or frequency is the number of waves that pass through a point in one second. is the number of vibrations in one second symbols of frequency = f f = Unit is waves per second or Hertz (Hz). n = number of wave , t = time 17

Example > 1 Hz = 1 wave per second. > 50 Hz is 50 vibrations in 1 second. 18

Test Yourselves Explain the meaning of 35 Hz, 100 Hz ,

Wave Period (T) It is the time it takes for one cycle to complete. It also is the reciprocal of the frequency. a particle move around circle. (fig. I) a period is a time move around circle. (fig. II) B B A’ A’ A C A A C O D D T

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 = 8 Hz  T = 1/8 s f = f Hz  s frequency is relate period in equation : Hz

Speed Of a Wave is the distance moved in one second. Wave speed is usually measured in meters/second, but may be measured using other distance units (such as centimeters per second).

Recall Speed of a motion = distance  time where v = speed, s = distance and t = time wavelength Distance of wave = = frequency

V = f Wave Equation Speed of a wave = wavelength  period = wavelength x frequency V = f Wave Equation where v = speed, f = frequency and  = wavelength

Example A wave is traveling at a speed of 12 m/s and its Wavelength is 3 m. Calculate the wave frequency. Solution 1. This is what you know : speed (v) = 12 m/s , wavelength( ) = 3m. 2. This is you want to find : wave frequency ( f ) 3. This is the equation you need to use : 4. Solve for f and then substitute the known value in the equation.

Example Solution This is what to know wavelength ( ) = 2m The wave in figure are traveling across water. Each wave is 2m long, so that wavelength is 2m. One second later 3 wave have passed the flag. Find wave speed. Solution This is what to know wavelength ( ) = 2m Frequency (f)= = 3 Hz. From

Problem

Question The in A below are traveling across water. Are the wave transverse or longitudinal? What is the wavelength of the wave? What is the amplitude of the wave? If 2 waves pass the flag every second, what is i) the frequency ii) the period? Use the wave equation to calculate the speed of wave in A? What is the wavelength of the wave in diagram B bellow? If the wave in B have the same speed as those in A, what is their frequency and period?

B 1. 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

2. Which wave is longitudinal ? A light B radio C sound D water C

D 3. 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 D

C 4. 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 Hint: v = f C

5. A VHF radio station broadcasts at a frequency of. 60MHz (6 5. 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 m B 0.5 m C 2.0 m D 5.0 m Hint: v = f D

Nov 1998 6. 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] C C C Wave length (continue in next slide)

(c) Is the wave on the spring more like a sound wave (Cont. …) Q 6 (c) Is the wave on the spring more like a sound wave or a light wave? [1] Sound wave, because sound wave is a longitudinal wave but light wave is a transverse wave..

7. The diagram below shows a transverse wave travelling a rope. wavelength amplitude (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] v = f = 0.8 x 2 = 1.6 ms-1

Nov 1996 8(a) Explain the difference between a transverse and a longitudinal wave. [2] 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. (b) State one example of each type of wave. Transverse Longitudinal [2] Light Sound

9.(a) Explain the difference between transverse and GCE ‘O’ LEVEL Nov 1995 9.(a) Explain the difference between transverse and longitudinal waves, referring in your answer to the direction in which the waves travel. [2] Transverse waves are waves that their direction of vibration is perpendicular to their direction of propagation. Longitudinal waves are waves that their direction of vibration is parallel to their direction of propagation. (continue on next slide)

(Cont. …) Q. 9 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 = f therefore 1500 =  250  = 1500 / 250 = 6.0 m

10. The diagram shows the air pressure at different distances from a loudspeaker. wavelength amplitude (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. (continue on next slide)

(Cont. …) Q. 11 11 (b) If the wavelength of a sound wave of frequency 250 Hz is 1.4 m, calculate the speed of the wave. [2] since v = f therefore, = 1.4 x 250 = 350 ms-1

11(a) With the aid of a diagram, explain what is meant by the frequency and wavelength of a wave. [5] Frequency is the number of vibrations per second. Wavelength is the distance from a point on a wave to its next corresponding point. It usually denote as ..  (b) What is a longitudinal wave ? [2] Longitudinal wave is a wave that its direction of vibration always parallel to the direction of propagation. (continue in next slide)