Wave front- plane wavefront

Circular wavefront

Types of waves(a) transverse wavevibration of particles in the medium is perpendicular to the direction of propagation of the wave, examples: light waves and water wave.

(b) longitudinal wavevibration of particles is parallel to the direction of propagation of the wave, example: sound wave.

Amplitude, period and frequency of waveAmplitude, A – is the maximum displacement from its equilibrium position. Period, T – is the time taken to complete an oscillation.Frequency, f – number of complete oscillations in one second, unit is hertz (Hz) or s-1

Relationship between period and frequency

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Graph of a waveDisplacement – time

Displacement – distance

Relationship between Speed (v), wavelength ( ) and frequency ( f )

Damping and ResonanceDamping – the decrease in amplitude, causes the amplitude and energy of the system to decrease.Resonance – occurs when a system is made to oscillate at frequency equals to its natural frequency by an external force. The system oscillates at maximum amplitude.

Effects caused by resonance: (a) Tuner in the radio or television enable to select the programmes.(b) Loudness of music produced by musical instruments such as trumpet.(c) Cause damage, examples: can collapse the bridge.

1.2 Reflection of waveDefinition/ explanation:- occurs when waves strike an obstacle

Laws of reflection: - angle of incidence, i is equal to the angle of refection, r- the incidence wave, the reflected wave and the normal line in the same plane, perpendicular to the reflecting surface at the point of incidence. - Wavelength, frequency and speed of wave do not change after reflection.- Direction of propagation of the wave changes.

Applications of reflection of waves in daily life: mirror – rear view mirror and side mirror in a car for safetyperiscope – viewing object beyond obstacles.Optical fibre – used in medication: to examine the internal organs of patient

Velocity = frequency x wavelengthv = f

used in telecommunication: to transmit informationRemote control – infrared waves from a remote control of television or radio are reflected by object in surroundings and received by television or radio.

1.3 Refraction of WavesDefinition/ explanation: - Change of direction when the speed of a wave changes as it moves from one medium to another. Refraction occurs.

Refraction of plane water waves- Water waves move from deep water to shallow water, the speed of waves change. - Water waves moves with higher velocity on deeper water than on shallow water.- The speed, wavelength and direction of waves change after refraction.- The frequency of waves do not change.

Effects of the water waves:the speed and wavelength water waves in the middle of the sea almost uniform/ same because the depth of the water is almost the same in the middle of sea. The distance between the wavefronts decrease as the water approach the beach. Because the depth of water decreases cause the waves change in its speed.The water in the bay stationary because the depth of water varies across the area of the bay. The energy of the water waves spread to a wider area compared to the cape. The amplitude of water waves near the bay is low.

Examples of refraction of water waves:

Refraction of Light ( refer notes in chapter 5 Light Form 4) Definition: when light propagates from one medium to a denser medium, the ray refracts towards the normal. When light propagates from one medium to a less dense medium, the ray refracts away the normal.

Applications of refraction of lightswimming pool look shallower than its actual deptha spoon in water appears benta boy’s legs look shorter when in a pool.

Refraction of sound wavesEffect: the sound at a distance can be heard clearer at night than in the day.Explanation: at night, the air close to the ground cooler than the layer further from the ground. Sound waves travel slower in cool air. The sound waves from a distance are refracted towards the ground due to the total internal refraction.

1.4 Diffraction of WavesDefinition: - waves spread out as they pass through an aperture or round a small obstacle.- frequency, wavelength and speed of waves do not change.- Direction of propagation and the pattern of waves change.

Effects of diffraction is obvious only if:- size of the aperture or obstacle is small - wavelength is large or frequency of vibration is low

Patterns of diffraction:

Diffraction of lightDefinition:- Light is diffracted when passes through a narrow slit comparable in size to its wavelength.- Diffraction of light is hardly noticeable compared with diffraction of sound waves and water waves because the wavelength of light is very short.

Light waves will be diffracted if: - light is propagated through a pin hole or a tiny slit where the size is similar to the light wavelength- the light source must be monochromatic (light consists of only one colour and one wavelength)

**sound waves are more easily diffracted compared to light waves because wavelength of sound is longer.

1.5 Interference of WavesDefinition:Superposition of two waves originating from two coherent sources producing waves of the same frequency (f), amplitude (A) and in phase.

Principle of superposition:- The wave displacement of the combined motion of any number of interacting waves at a point is the sum of the displacements of all the component waves.- The superposition of two waves is either constructive or destructive interference.- Constructive interference – when the crests or troughs of both waves coincide to produce a wave of maximum amplitude. - Destructive interference – when the crest of one wave coincides with the trough of the other wave resulting zero amplitude.

Antinode – a point where constructive interference occursNode – a point where destructive interference occurs.

Relationship between , a, x and D

= wavelengtha = distance between two coherent sourcesx = distance between two consecutive node or antinode linesD = distance from the two sources to the point of measurement of x

Interference of Light WavesWaves emitted from two coherent sources have the same frequency (or wavelength) and in phase.

Young’s Double slit experiment

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Interference of sound waves- Coherent sound waves interfere with each other to produce areas of louder sound and softer sound.- Constructive interference occurs at the area of louder sound whereas destructive interference occurs at the areas of softer sound.

1.6 Sound WavesDefinition/ explanation of Sound waves- longitudinal waves which require a medium for its propagation.- produced by vibrations- speed of sound is unaffected by pressure- speed of sound increases with temperature- loudness of sound is affected by the amplitude of the sound waves.- Pitch of sound is affected by the frequency of the sound waves.

Relationship between Speed (v), wavelength ( ) and frequency ( f )

Application of sound waves:(a) Using ultrasonic waves to remove plaque from teeth(b) Using high frequency sound waves to dislodge dirt particles adhering to jewellery.

Velocity = frequency x wavelengthv = f

(c) Use Sonar (Sound Navigation and Ranging) to detect underwater object or to determine the depth of water.(d) Use sonar to detect the location of fish.(e) Use high-energy sound waves to destroy the kidney stone.(f) Use the reflection of sound waves to determine the distance between two objects.

1.7 Electromagnatic WavesElectromagnetic spectrumDefinition/ Explanation:Consists of electric and magnetic components oscillate at right angles to each other and to the direction of propagation.

Properties of electromagnetic waves:(a) The waves travel at the speed of light, 3.0 x 108ms-1 in vacuum(b) Do not require a medium to propagate and can travel in vacuum(c) Transverse waves(d) The magnetic and electric field components of the wave oscillate at right angles to each other and to the direction of propagation of the waves.(e) Obey the waves equation, c = f, c is velocity of light, f is frequency and is wavelength(f) Undergo the same phenomena: reflection, refraction, diffraction and interference(g) Are electrically neutral (h) Show polarisation

Radio waves

Microwaves Infrared Visible light

Ultraviolet X-ray Gamma ray

Frequency increase

Wavelength increase