1026882 nota padat fizik f5 waves

7/28/2019 1026882 Nota Padat Fizik F5 Waves

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6.1 WAVES

What iswaves?

Process of transferring energy from one location to anotherwhich is produced by an oscillating or vibrating motion.

Examples ofwaves

Light waves are produced as a result of vibrations ofelectrons in an atom

Sound waves are produced by vibrating mechanical bodiessuch as a guitar strings or a tuning fork.

Water waves are produced by a disturbance on a still water

surface.

How dowavestransferenergy?

When energy is transferred by a wave from a vibratingsource to a distant receiver, there is no transfer of matterbetween the two points.

When the string is shaken up and down, adisturbance moves along the length of thestring. It is the disturbance that moves alongthe length of the string, not parts of the stringitself.

The energytransferred from avibrating source toa receiver is carriedby a disturbance in


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a medium, not bymatter moving fromone place toanother within themedium

Drop a stone in a quite pond. It will produce awave that moves out from the center in expandingcircles. It is the disturbance that moves, not thewater. After the disturbance passes, the water iswhere it was before the wave was produced .

The string and water is the medium through whichwave energy travels.

What is

TransverseWave?

A transverse wave is a wave in which the vibration ofparticles in the medium is at right angle to the direction ofpropagation of the wave.


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The spring is moved sideways. The motion of the particlesmedium (spring) is at right angles to the direction in which thewave travels.

Examples: water waves, light waves

What isLongitudinal Waves?

A longitudinal wave is a wave which the vibration of particlesin the medium is along (parallel to) the direction ofpropagation of the wave.

The slinky spring moves backwards and forwards to producea transverse wave. The particles of the medium (spring) movealong the direction of the wave. The wave that travels alongthe spring consists of a series of compression and

rarefaction.

Examples: sounds waves.


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What is a ripple tank?

The phenomenon of water waves can beinvestigated using a ripple tank.

The water waves are produced by avibrating bar on the water surface.

The tank is leveled so that the depth ofwater in the tank is uniform to ensurewater waves propagate with uniformspeed.

The water acts as a lens toproduce a pattern of bright

and dark regions on a piece ofwhite paper placed under thetank when light passesthrough it.

Water waves have crests andtroughs.

A crest is the highest positionof the wave acts as a convexlens, whereas a trough is the

lowest position acts as aconcave lens.

Light rays from the lamp ontop will focus onto the whitescreen below. The brightlines correspond to thecrests, and the dark linescorrespond to the troughs.


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What is meant by a wavefront?

Lines joining all the points ofthe same phase are calledwavefronts.

The wavefronts of a transversewave and longitudinal wave areperpendicular to the directionof propagation of the waves.

1. Plane wavefronts

2. Circular wavefronts

Describing Waves

Vibration/Oscillation

The movement fromone extreme position tothe other and back tothe same position.

Amplitude (a)

The maximum displacement from its equilibrium

position.

Amplitude relates to loudness in sound andbrightness in light. SI unit: meter, m

Wavelength (.)

The distance between two adjacent points of the


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same phase on a wave.

The distance betweentwo successive crestsor two successivetroughs

The distance betweentwo successivecompressions or twosuccessive rarefactionsin a sound wave.


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Period (T)

The time taken for anoscillation to completeone cycle.

SI unit is second (s).

Frequency, f

The number of wavesproduced in onesecond.

SI unit is Hertz (Hz)

Relation betweenfrequency and period:

Tf1=

Wave Speed (v)

The speed of a wave isthe measurement ofhow fast a crest ismoving from a fixedpoint.

SI unit is ms-1.

The relationship between speed, wavelength and

frequency

Velocity = wavelength x frequency

v = f.

Displacement-time graph

Displacement-distance graph

Velocity , v = f.

Example 1


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From the graph,calculate:

(a) Amplitude

(b) Period,

(c) Frequency


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Example 2

A graph shows a waveproduced by a slinkyspring vibrating atfrequency 8 Hz. Whatis:

(a) amplitude

(b) wavelength

(c) wave speed

What isdamping?

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 graduallydecrease and become zero when the oscillation stops.

Whatcausesdamping?

1. External damping of the system is the loss of energy toovercome frictional forces or air resistance.2. Internal damping is the loss of energy due to theextension and compression of the molecules in the

system.

A graph toshowdamping

External


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Force

Forceoscillation

Naturalfrequency

.. To enable an oscillating system to go on continuously,an external force must be applied 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 freelywithout the action of an external force is called thenatural frequency.


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Resonance

.. Resonance occurs when a system is made to oscillateat a frequency equivalent to its natural frequency by anexternal force. The resonating system oscillates at itsmaximum amplitude.

Experimentin Bartonspendulum

How doesresonanceoccur inthe twopendulumof equallength?

.. The frequency of a simple pendulum depends on thelength of the pendulum... In Bartons pendulum experiment, there are manypendulums tied to the rope. Two of the pendulum are ofthe same length

.. When pendulum Boscillates, all the otherpendulums are forced tooscillate... But pendulum D

oscillates with the largestamplitude, ie, pendulumD resonates


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.. Pendulum B and pendulum D are of the same length.

.. Frequency B = Frequency D

.. Therefore, pendulum B causes pendulum D to oscillateat its natural frequency.

Goodeffects ofresonance

1. The tuner in a radio or television enables us to selectthe programmes we are interested. The circuit in thetuner is adjusted until resonance is achieved, at thefrequency transmitted by a particular station selected.Hence a strong electrical signal is produced.2. The loudness of music produced by musicalinstruments such as the trumpet and flute is the resultof resonance in the air.

Bad effectsofresonance

3. A bridge can collapse when the amplitude of itsvibration increases as a result of resonance.


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6.2 REFLECTION OF WAVES

Reflection ofwave

.. Occurs when a wave strikes an obstacle.

.. The wave undergoes a change in direction ofpropagation when it is reflected... The value of frequency (f), wavelength (.) and speed (v)remain the same after reflection.

Incident wave : the wave before it strikes theobstacle

Reflected wave: the wave which has undergonea change in direction of propagation afterreflection.

i = angle of incident the angle between thedirection of propagation of incident waveand the normal

r = angle of reflection the angle between thedirection of propagation of reflected waveand the normal.

Law of Reflection:

The angle of incidence, i

is equal to the angle ofreflection, r.

Reflection of plane water waves in aripple tank

1. Set up a ripple tank.2. Switch on the motor to set the


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vibrating. Increase the frequencyof the waves by increasing thevoltage power supply to the motor.3. Observe the reflected wave byusing a stroboscope.

Draw adiagram toshowreflection ofwaves.


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6.3 REFRACTION OF WAVES

What isRefractionof waves?

Refraction of waves is a change in its direction as the wavespass from one medium to another. It occurs when there is adifference in the speed of the wave at the boundary of twomediums.

Whathappens tofrequency,speed,wavelength& direction?

After refraction, the wave has the same frequency, but a

different speed, wavelength and direction of propagation.

The relationship between v and .of a water wave in deep andshallow water:

v = f. f is constant

...v v is directly proportional to .

2211tanfvfvtconsvf=.==.

Use thewords,increase,decreaseorunchanged


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Characteristics

Water wavespasses fromdeep water toshallow water

Characteristics

Water wavespasses fromshallow waterto deep water

Speed

Decrease

Speed

increase

Wavelength

Decrease

Wavelength

Increase

Frequency

unchanged

Frequency

unchanged


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How doesthedirection ofwaveschangewhen:

Water passing from the deepregion to the shallow region,the water wave is refractedtoward the normal.

Water passing from the shallowregion to the deep region, thewater wave is refracted awayfrom the normal.


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Use a rippletank

Draw a raydiagram toshowrefraction ofwaves.

Example 1

A plane wave has a wavelength of 2cm and a velocity of 8 cm s-1 as itmoves over the surface of shallowwater. When the plane wave movesinto an area of greater depth, itsvelocity becomes 12 cm s-1. What is

(a) the wavelength

(b) the frequency

of the wave in the area of greater


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depth?


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Example 2

The diagram shows a plane waterwave moving from one area P toanother area Q of different depth.

If the speed of water wave in P is 18cm s-1, what is the speed of waterwave in Q?

6.4 DIFFRACTION OF WAVES

What isdiffraction ofwaves?

Diffraction of waves is a phenomenon in which wavesspread out as they pass through a gap or round a smallobstacle.

What areCharacteristicsof diffractedwaves?

1. Frequency, wavelength and speed of waves do notchange.2. Changes in the direction of propagation and the pattern ofthe waves.3. The amplitude of the diffraction wave decreases so itsenergy decrease.

What are thefactors thatinfluence theeffect ofdiffraction?

The effect of diffraction is obvious if:


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1. the size of the gap or obstacle is small enough2. the wavelength is large enough.

The effect of diffraction is obvious if the shape of thediffracted waves more spread out or more circular


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Diffractionof sound

Sound diffractingaround corners soallowing us to hearothers who arespeaking to us fromadjacent rooms.

Diffractionof light

Light is diffracted if itpasses through a narrowslit comparable in size toits wavelength.

However, the effect is notobvious as the size of theslit increases. This is

because the wavelengthsof light are very short.

We can hear the soundof a radio placed nearbya corner of a wall but wecannot see the radio.Why?

Sound waves are more easily diffracted incomparison to light waves because thewavelength of sound waves is much longer thanthe wavelength of light waves.

Procedure

.. A ripple tank is filled with water andset up as shown.

.. Switch on the power pack.

.. Use a barrier to block the incidentstraight water waves. Observe thewave pattern beyond the barrier... Send a straight water waves to passthrough a gap. Observe the pattern ofdiffracted waves beyond the gap... Send straight water waves towards asmall gap. Observe the wave patternbeyond the small gap.


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Observation

(a) Wide gap

The waves are bend only at theedges after passing through thegap.

The effect of diffraction is notobvious

(b) Narrow gap

The waves are circular and appearto originated from the small gap.

The effect of diffraction is obvious

Straight water wave propagatetowards an obstacle.

As the size of the gap or obstacle is smaller , the effect of diffractionbecomes obvious.


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6.5 INTERFERENCE OF WAVES

State thePrinciple ofsuperposition ofWaves

When two waves interfered, the resulting displacementof the medium at any location is the algebraic sum ofthe displacements of the individual waves.

(a) Superpositionof two crests

(b) Superpositionof twotroughs

(c) Superpositionof a crest anda trough


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ConstructiveInterference


Destructive

Interference

What isInterference ofWaves?

.. Interference is the superposition of two waves

originating from two coherent sources.

What is coherentsources?

.. The waves from coherent sources have the samefrequency (f), same wavelength and constant phasedifference.

How doesinterferenceoccur?

.. Wave interference occurs when two waves meetwhile propagating along the same medium... When the two waves are superposed, interferencewill occur either constructive interference ordestructive interference.


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.. Occurs when the crests or troughs of both wavescoincide to produce a wave with crests and troughsof maximum amplitude.

Destructiveinterference

.. Occurs when crest of one wave coincide with thetrough of the other wave, thus canceling each otherwith the result that the resultant amplitude is zero

The occurrenceof constructiveinterference

and

destructiveinterference

Antinode

Node

Keys:

Maximumcrest wave


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(2 crestsmeet)

Zeroamplitude(troughmeets crest)

Maximumtrough wave(2 troughsmeet)

.. A point where constructive interference occurs

.. A point where destructive interference occurs.


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Youngs formula

The relationshipbetween ., a, xand D

Dax=.

a = distance betweentwo coherentsources

. = wavelength

x = distance between

two consecutive

node (or

antinode) lines

D = distance from the

two sources tothe point ofmeasurement ofx


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Factors affectingthe interferencepattern

The interference pattern depend on the value of x

When x changes, the interference pattern also changes

aDx.=

1. ax1.

The distance between 2 consecutive lines, x isinversely proportional to the distance between 2sources,a

As a becomes larger, xbecomes smaller

As a becomes smaller, xbecomes larger


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2. ..x

where a & D areconstant

The distance between two consecutive node lines orantinode lines , x increases is directly proportional tothe wavelength of the wave , .

Low frequency (large .)

As . increases, xincreases

High frequency (small .)

As . decreases, x alsodecreases.

3. Dx.

x directlyproportional to D

where a & . areconstant

The distance between twoconsecutive node lines orantinode lines, x is directlyproportional to the distancefrom the two sources to the

point of measurement of x, D

Interference of lights


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Occurs when an incident light wave passesthrough a double slit.

An interference pattern is produced as a resultof the superposition of two emerging lightwaves from the double slit.

Youngs double-slitexperiment

.. Use monochromatic light (light which hasone colour and one wavelength).. The double slit must be very narrow (about0.5 mm) to produce a clear interferencepattern because the wavelength of light isvery small.

.. When light from monochromatic sourcepasses through a double slit, two sources ofcoherent light are produced.


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Dax=.

.. The interference pattern consists of alternatebright and dark fringes that can be seen on adistant screen... Bright fringes: constructive interference.. Dark fringes: destructive interference.

a = Distance between the two slits on the double slitplate

D = Distance between the double-slit plate and thescreen

. = The wavelength of light depends on its color.

x = Distance between two consecutive bright fringesor dark fringes.

Interference of SoundWaves

Occurs when two coherent sound waves interacton the basis of the principle of superposition toproduce a pattern of

a= the distance betweenthe two loudspeakers

D = Distance between theloudspeakers and thepath along whichinterference can bedetected

. = The wavelength ofsound waves is


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The two loud speakers are the sources of the twocoherent sound waves as they are connected tothe same audio signal generator.

A student is requested to walk in a straight path ata distance of D from the loudspeakers.

The student hears alternating loud and softsounds as he walks along the straight path.


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influenced by thefrequency of the audiosignal generator.

x = Distance between twoconsecutive positionswhere loud sound isheard

The alternating loud and soft sounds is caused byinterference of the sound waves.

The loud sound: constructive interference

The soft sound : destructive interference.

Dax=.

Water wave

Sound wave

Light wave

.

The wavelength of water

waves is influenced bythe frequency of thevibrator

The wavelength ofsound waves isinfluenced by thefrequency of the audiosignal generator.


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The wavelength of lightdepends on its color.

D

Distance between thespherical dippers and theposition marked x ismeasured

Distance between theloudspeakers and thepath along whichinterference can bedetected

Distance between thedouble-slit plate and thescreen

a

Distance between the twospherical dippers

Distance between thetwo loudspeakers

Distance between thetwo slits on the doubleslit plate

x

Distance between twoconsecutive antinodelines or two consecutive

node lines

Distance between twoconsecutive positionswhere loud sound isheard

Distance between twoconsecutive brightfringes or dark fringes.

High amplitude of water

Calm water

Loud sound

Soft sound

Bright fringes


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Dark fringes


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Example 1

In the interference of two coherentsources of waves, the separation betweentwo spherical dippers is 3 cm and thedistance between two consecutive nodelines is 4 cm measured at a distance of 15cm from the two coherent sources ofwaves. Calculate the wavelength of thewater waves originating from the sources.

Example 2

In a Youngs double slit experiment, thedistance between the double slit and thescreen is 4.0 m and the separation of thetwo slits is 0.5 mm. calculate the distancebetween two consecutive bright fringesfor violet light with a wavelength of4.0 x 10-7 m

Example 3

The wavelength of light can be determinedwith a double-slit plate. The diagramshows the pattern of interference fringesobtained in a Youngs double-slitexperiment. The separation of distance ofthe two slits is 0.25 mm and the distancebetween the screen and the double slitplate is 3.0 m.

Calculate the wavelength of light used inthe experiment.


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Example 4

In an experiment on the interference ofwaves, two loudspeakers are placed at adistance of 1.5 m from each other. Theyare connected to an audio signalgenerator to produce coherent soundwaves at a frequency of 0.5 kHz.Calculate

(a) the wavelength of the sound waveif the speed of sound is 300 ms-1(b) the distance between twoconsecutive soft sounds at aperpendicular distance of 5 m fromthe source of the sound.


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6.6 ANALYSING SOUND WAVES

What issoundwaves?

Sound is a form of energy propagated as waves that makeour eardrums vibrate.

Sound waves are caused by vibrating objects.

Sound waves are longitudinal waves.

How issoundproduced bya vibrating

objects?

Sound waves are produced when a vibrating objectcauses the air molecules around it to vibrate.

When a tuning fork vibrates, layers of air vibrate and thesound energy is propagated through the air around it inthe form of waves. When the tuning fork moves forwards, the air iscompressed.

When the tuning fork moves backwards, the air layersare pulled apart and cause a rarefaction. Therefore, a series of compression and rarefactions willproduce sound.

Why doessound wavesis alongitudinal

waves?

The air particles vibrate backward and forward in thedirection parallel to the direction of propagation of thesound wave. Wavelength of sound, . = the distance between twosuccessive regions of compression or two successiveregions of rarefaction.


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Explain howthe loudnessrelates toamplitude?

The loudness of the sound depends on its amplitude. If the amplitude is increased, the loudness increases.

Explain how

A high pitch sound corresponds to a high frequency and


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the pitchrelates tofrequency

a low pitch sound corresponds to a low frequency ofvibration.

To investigate the relationship between the amplitude and the loudnessof sound

The audio signal generator is switched on and the frequency of thesound wave is adjusted to a suitable level. The loudness of the sound isvaried from a lot to a high level gradually. Observe the shape of thesound wave displayed on the screen of oscilloscope.

Write: low / medium / high

Wave form

Amplitude ofsound wave

Loudness ofsound

The relation between the pitch and the frequency of sound

The audio signal is switched on and the loudness is adjusted to asuitable level. The frequency of the sound is varied from low to highgradually. The pitch of the sound that is heard and the form of the wavedisplayed on the screen of the oscilloscope is observed.


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Write: low / medium / high

Wave form

Frequency ofsound wave

Pitch of sound


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describe applicationsof reflection of soundwaves.

Ultrasound inmedicine

Sonar

The reflection of sound is called echoes.

Infrasound

Normalaudible range

Ultrasound

Less than 20Hz

20 Hz to


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20 000 Hz

Higher than

20 000 Hz.

Ultrasound waves is used to scan and capturethe image of a fetus in a mothers womb andthe image of internal organ in a body. Transmitter P emits ultrasound downwards tothe fetus. Detector R receives the ultrasound (echoes)reflected by the various parts of the fetus. The soft tissues of the fetus absorb most ofthe incident ultrasound, reflect very little. Thebony parts will absorb very little, but reflectmost of the ultrasound. The reflectedultrasound will produce an image ofcontrasting brightness.

Sonar is the technique of using ultrasound tolocate underwater objects or to measure thedepth of a seabed. Ultrasound signal is sent out from atransmitter. Its echo from the seabed is detected by areceiver which is connected to an electrical

recording circuit. The time interval, t between the sending andreceiving of the ultrasound signal afterreflection from the seabed is measured.


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A bat can navigate indarkness

The depth of the seabed, 2tvd= where v isthe velocity of sound in water.

When ultrasonic waves emitted by the bat hitan object, they are reflected back and receivedby the bat. The time between the emission of the soundwaves and reception of the reflected wavesenables the bat to estimate the position of theobject accurately. This enables the bat to adjust its direction to

avoid knocking at the object.

Calculatedistancesusing thereflection ofsound waves.

An ultrasonic wave is used to determine the depth of a seabed. Apulse of ultrasound is generated and travels to the seabed andreflected by it. The time taken by a pulse of ultrasonic wave totravel to and fro the seabed is 0.28 s. It the speed of sound in the

water is 1 500 ms-1, calculate the depth of the seabed.


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6.7 ANALYSING ELECTROMAGNETIC WAVES

Describe the electromagnetic spectrum

l------------Radio waves--------l

h

What iselectro-magnetic

It consists of a group of waves with similar natuThe members of the electromagnetic spectrum

arranged in increasing frequencies and decreasingwavelengths are radio waves, microwaves, infraredrays, vrays.Radio waves have the longest wavelength but are oflow frequency waves. They carry very little energy.Gamma rays have the shortest wavelength but are of

What is telectro-magnet

It is produced when electric aat right angle to each other.The direction of propagation

low frequency high frequency


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State thevisiblelight is apart of theelectro-magneticspectrum

Visible light waves are the only electromagnetic waveswe can see. Light can be seen as the colours ofrainbow. Each colour has a different wavelength. Red has the longest wavelength and violet the shortest. When all the waves are seen together, they make whitelight. When white light shines through a prism, the white lightis broken apart into the seven colours of the visiblelight spectrum. Red, orange, yellow, green, blue, indigo and violet.

Describethepropertiesof electro-magneticwaves

1. They transfer energy from one point to another.2. They are transverse waves.3. They can travel through vacuum.

4. They travel at the same speed through vacuum, i.e atthe speed of light , c = 3 x 108 ms-1.5. They all show wave properties such as reflection,refraction, diffraction and interference.6. They obey the wave equation, v = f..

List sources of electro-magnetic waves and the applications.

Electromagneticwave

Sources

Applications


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Gamma Rays

Radioactivesubstances

Engineering to detect leakagesin underground pipes Medicine cancer treatment Food sterilisation


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X- rays

x-ray tube

Medicinei. X-ray photograph of theinternal organs of the body,e.g to locate bone fracture.ii. Cancer treatment

Engineering to detect cracks inmetal Checking of luggage at airports

Ultraviolet rays

The sun,mercuryvapour

lamp.

Cause sunburn Stimulates the formation ofvitamin D needed for assimilationof calcium and the prevention ofrickets. Detect fake notes Fluorescent lamp Sterilization of surgical tools andplant seedlings.

Visible light

Flames,lamps,

the sun

Visual communication Photography Photosynthesis

Infraredradiation

Hot objectssuch as


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flames, thehumanbody, thesun

A sensation of warmth is feltwhen IR falls on the skin. Thermal imaging andphysiotherapy Infrared binoculars for night timevision. IR radiation emitted by aliving thing can be detected. Remote control for TV / VCR

Microwaves

Radartransmitter

Microwavesoven

Communication system with

satellites Used in radar system Cooking Cellular (mobile) phone service

Radio waves

Electronsoscillatingin aerials

Radio/

television

For broadcasting and wirelesscommunication UHF (ultra high frequency) radiowaves television and handphones


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transmitter

VHF (very high frequency) radiowave local radio FM andwireless communication used bythe police

Describe the detrimental effects of excessive exposure to certaincomponents of the electromagnetic spectrum.

Radio waves

No evidence of hazard

Microwaves

Internal heating of body tissues when they enterour body.

Long exposure to mobile phones can causebrain tumor and inner ear complications inchildren. Just SMS.

Infrared

Skin burns

Visible light

No evidence of hazard

Ultraviolet

Damage to the surface cells (including skincancer) and blindness

X-rays

Damage to cells.

Cancer, mutation

The mutated cells may result in the abnormalgrowth of cancer cells.


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Pregnant mothers who are exposed to X-raysand radiations too frequently may causeabnormalities in new born babies.

Gamma rays


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