Section 3 Properties of Waves, Including Light and Sound

PAL (IGCSE) – PHYSICS Section 3 Properties of Waves, including Light and Sound

Properties of Waves Including Light and Sound

PAL (IGCSE) Single Science Revision Book - Section 3

Name: ______

Teacher: ______

DIPONT Educational Resource – Science 1 PAL (IGCSE) – PHYSICS Section 3 Properties of Waves, including Light and Sound

Syllabus Content______

Syllabus Details______

3.1 General wave properties Core • Describe what is meant by wave motion as illustrated by vibration in ropes and springs and by experiments using water waves Water Surface Oscillation or Rope

Energy Transfer Forced oscillation

WAVE MOTION: Waves carry energy without the net movement of particles

NOTES PAGE

• Use the term wavefront

Waves in Water Wave front diagram

Ray diagram

WAVEFRONT: Line connecting points with the same phase.

• Give the meaning of speed, frequency, wavelength and amplitude x

, t T n e m e c a l p

s A i D

Time /s

In Phase positions Mean position x

t l n e m e c a l p

s A i D

Position /m

One complete oscillation

Term Symbol Definition Amplitude A Maximum displacement from the mean position Frequency f The number of oscillations that take place in 1 second Wavelength  Shortest distance between two points in phase with one another. Wave speed v The speed at which wave fronts pass a

stationary observer

NOTES PAGE

• Distinguish between transverse and longitudinal waves and give suitable examples

Transverse Waves Oscillations perpendicular to direction of energy transfer

Energy transfer

Longitudinal Waves Oscillations parallel to direction of energy transfer

Energy transfer

• Describe the use of water waves to show: – reflection at a plane surface

Reflection at a plane surface

Normal

NOTES PAGE

– refraction due to a change of speed

Refraction in water

Wave Speed High

Deep water

Shallow water

Wave Speed Low

– diffraction produced by wide and narrow gaps

Diffraction

Supplement • Recall and use the equation v = f λ

v = velocity (wave speed) [m/s] f = frequency [Hz] v = f l l = wavelength [m]

• Interpret reflection, refraction and diffraction using wave theory

See above

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3.2 Light 3.2 (a) Reflection of light Core • Describe the formation, and give the characteristics, of an optical image by a plane mirror

Image: • Imaginary • Upright • Same size as object • Laterally inverted • Same distance from the mirror as the object

• Use the law angle of incidence = angle of reflection

Mirror Surface

Angle of Reflection

Angle of Incidence

Angle of Incidence = Angle of Reflection

Supplement • Perform simple constructions, measurements and calculations

NOTES PAGE

3.2 (b) Refraction of light Core • Describe an experimental demonstration of the refraction of light

A Stick in Water

Air Water

• Stick appears closer to the surface of the water than it actually is • Virtual Image

• Use the terminology for the angle of incidence I and angle of refraction r and describe the passage of light through parallel-sided transparent material normal

Refraction of Light

Glass block

Refraction of Light

normal Incident ray Angle of Incidence

Less Dense Material

More Dense Material

Angle of Refracted ray Refraction

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• Give the meaning of critical angle

CRITICAL ANGLE: The angle of incidence beyond which light will totally internally reflect

• Describe internal and total internal reflection

Partially transmitted Less dense

Grazing Emerging

Critical angle Totally Reflected

Partially reflected More dense

• If the angle of incidence > critical angle light will totally internally reflect

Supplement • Recall and use the definition of refractive index n in terms of speed • Recall and use the equation sin i /sin r = n

normal Incident ray

Medium (n)

r Refracted ray

Sin i v (air) = n = n Sin r v (medium)

NOTES PAGE

• Describe the action of optical fibres particularly in medicine and communications technology

Optical Fibers

Optical Fibers • Light is guided down the fiber. • The light will always internally reflect if the angle of incidence > critical angle • Optical fibers are used… • for transmitting data • for carrying pictures from inside the human body - ENDOSCOPE

3.2 (c) Thin converging lens Core • Describe the action of a thin converging lens on a beam of light • Use the term principal focus and focal length

Converging Lens Principle focus

Focal Length

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• Draw ray diagrams to illustrate the formation of a real image by a single lens

Distant Object CONVERGING LENS Object

f f Image

Object at 2f

Object

f f Image

Object between 2f and f

Object f f Image

Supplement • Draw ray diagrams to illustrate the formation of a virtual image by a single lens

Object between f

Object f f

Object closer than f

f Object f

NOTES PAGE

Distant Object DIVERGING LENS

Object f Image f

Object at f

Object f Image f

Object closer than f

Object

f Image f

• Use and describe the use of a single lens as a magnifying glass

Magnifying glass

f Object f

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3.2 (d) Dispersion of light Core • Give a qualitative account of the dispersion of light as shown by the action on light of a glass prism

Dispersion of White Light by a Prism

red Increasing Frequency blue

 The refractive index is different for individual frequencies  The degree of refraction will increase with increasing frequency

3.2 (e) Electromagnetic spectrum Core • Describe the main features of the electromagnetic spectrum and state that all e.m. waves travel with the same high speed in vacuo

Electromagnetic Spectrum

Wavelength

3 x 104 m 3 m 3 x 10-4 m 3 x 10-8 m 3 x 10-12 m

Infrared Gamma rays Radio waves Ultraviolet

Microwaves X-rays

104 Hz 108 Hz 1012 Hz 1016 Hz 1020 Hz

Frequency 7.5 x 10-7 m 4 x 10-7 m

4 x 1014 Hz 7.5 x 1014 Hz Visible Light

The speed of electromagnetic waves in a vacuum is constant

NOTES PAGE

• Describe the role of electromagnetic waves in: – radio and television communications (radio waves)

Radio Waves: Used to transmit radio and television signals from transmitters to houses etc. The information is stored in the frequency and amplitude of the wave

Modulated Carrier Wave

For long distance transmission of signals…

• A high powered carrier wave is used • A low intensity signal is added to the carrier wave • The signal is carried ‘on the back’ of the carrier wave

Frequency Modulation Amplitidue Modulation

NOTES PAGE

– satellite television and telephones (microwaves)

Microwaves: Used to transmit data to and from land based and satellite receivers. These transfer telephone and television signals. Microwaves are effective over long distances

– electrical appliances, remote controllers for televisions and intruder alarms (infrared)

Infrared:  Used on remove controls for short transfer of data to the television from the remote control  Detected by intruder alarms as IR is strongly emitted from hot objects like humans

– medicine and security (X-rays)

X-rays:  Used to view inside humans as they are weekly absorbed by skin but more strongly absorbed by bone  Used to view inside bags etc as weakly absorbed by the “skin” of a bag but strongly absorbed by metallic objects like knives

• Demonstrate an awareness of safety issues regarding the use of microwaves and X-rays

Safety issues of microwaves:

 Microwaves interact very strongly with water causing it to vibrate and so get hot.  This will also happen inside the human body as we are predominantly water

Safety issues of X-rays:

 X-rays are very high energy electromagnetic waves and will have an ionizing effect on the human body.  Over exposure to X-rays can cause cancer

Supplement • State the approximate value of the speed of electro-magnetic waves

Speed of electromagnetic waves in a vacuum: 300 000 000 m/s

• Use the term monochromatic

Monochromatic light: Light consisting of a single wavelength or frequency

NOTES PAGE

3.3 Sound Core • Describe the production of sound by vibrating sources • Describe the longitudinal nature of sound waves

Oscillation

Wave motion

Oscillating Source Air particles

 The vibrating source “pushes” the air particles  The particles in front of the vibrating source also vibrate  A longitudinal wave is created

• State the approximate range of audible frequencies

Frequency Hz 0.1 1 10 100 1000 10000 100000 1000000

Subsonic Human Hearing ultrasonic

HUMAN HEARING RANGE: 20 – 20000 Hz

• Show an understanding that a medium is needed to transmit sound waves

 Sound waves are vibrations in air particles  If there are no air particles present, no sound can be transmitted

• Describe an experiment to determine the speed of sound in air

 Measure out a distance of a few 100 meters  Have one person with a starter pistol at one end of the measured distance  At the other end of the measured distance a person measures the time between seeing the smoke from the starter pistol and hearing the sound  We can assume that the light from the smoke gets to the timer immediately as the speed of light is much faster than sound.  The speed of sound can be calculated from the distance and time interval

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• Relate the loudness and pitch of sound waves to amplitude and frequency

High frequency = High Pitch Low frequency = Low Pitch

Low amplitude = Quiet High amplitude = Load

• Describe how the reflection of sound may produce an echo

Sound waves

Supplement • Describe compression and rarefaction Longitudinal Waves

Compression

Rarefaction

COMPRESSION: Area of high pressure

RAREFRACTION: Area of low pressure

NOTES PAGE

• State the order of magnitude of the speed of sound in air, liquids and solids

SPEED OF SOUND:

 AIR = ~340 m/s  LIQUIDS = ~1500 m/s (water)  SOLIDS = ~5000 m/s (steel)

DIPONT Educational Resource – Science 40