waves chapter 1 form 5

PHYSICS FORM 5 [ CHAPTER 1: WAVES] Department of Physics SSI

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1.1 UNDERSTANDING WAVES

1. Waves are everywhere. Whether we recognize or not, we encounter waves on a daily basis. Sound waves, visible

light waves, radio waves, microwaves, water waves, sine waves, cosine waves, telephone chord waves, stadium

waves, earthquake waves, waves on a string, and slinky waves and are just a few of the examples of our daily

encounters with waves.

2. Waves are ______________________. They transfer energy from one location to another. Radio waves carry

energy from the transmitter to the receiver. The sound waves carry energy from the radio to our ears.

3. Figure 1 shows that the cork does not move outwards as the wave passes. This means that the water itself does not

move outwards. Through wave motion, energy is transferred from the source to a receiver without involving the

transfer of matter.

Figure 1

4. Transverse Wave

(a) A Transverse wave is a wave in which

_______________________________________________________________________________________

_______________________________________________________________________________________

(b) A model of transverse wave can be produced by a slinky spring as shown.


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(c) Examples of transverse wave:

(a) ___________________________________________

(b) ___________________________________________

(c) ___________________________________________

5. Longitudinal Waves

(a) A longitudinal wave is a wave in which _______________________________________________________

_______________________________________________________________________________________

(b) When the slinky spring is vibrated back and forth along the direction of propagation of the wave at a fixed

rate, a longitudinal wave is produced as shown.


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(c) Examples of longitudinal wave are __________________

Air particle vibrate to and fro to produce sound

6. Wavefront is an imaginary line that connects all vibrating particles that are in the same ___________.

7. Wavefront can be drawn by joining all the crests of a wave or by joining all the troughs.

8. The direction of propagation of the wave is always _________________ to the wavefronts.

Circular Wavefronts

Produced when a fingertip touch the surface of water repeatedly

Plane Wavefronts

Produced when a wooden bar vibrates vertically at a constant frequency on the surface of water

Direction of wave propagation

Direction of the vibration of particles in medium


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Amplitude, Period and Frequency

1. Equilibrium position is ______________________________________________________________________

2. One complete oscillation of the pendulum occurs when the pendulum bob moves from ____________________

3. The amplitude, A of vibrating system is the maximum displacement from its equilibrium position.

4. The period, T of vibrating system is ______________________________________________________________

T = nsoscillatiocompleteofNumber

ttaken,Time

The SI unit of period is second, s.

5. The frequency, f is the ________________________________________________ made by a vibrating system in

________________________

Frequency, f = T

1

The unit of frequency is hertz (Hz) or s-1.

T is inversely proportional to f and vice versa.

Displacement-Distance Graph and Displacement-Time Graph

Figure 1

Figure 2

1. From the graph of displacement, s against time, t in figure 1, the following information is obtained.

(a) Amplitude, A = _____________

(b) Period of oscillation, T is the time between points _____________

2. From the graph of displacement, s against distance, d in figure 2, the following information is obtained.

(a) Amplitude, A is the maximum displacement of a medium particle from its stationary position. The height of

a crest or the depth of a through equals the amplitude of the wave.


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(b) Wave length, __________________________________________________________

3. Relationship between Speed (v), Wavelength (λ) and Frequency (f):

Velocity = Frequency x Wavelength

v = f x λ

Damping

Figure 6.12

Figure 6.13

1. Damping is a process whereby the ________________________________________ until the system stops

oscillating.

2. Damping is usually caused by :-

(i) ____________________________________________________________________________________

(ii) _____________________________________________________________________________________

3. Damping in an oscillating system causes the ________________the ________________ of the system to

________________ but the _________________________________________


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4. The frequency of a system which _________________________ without the action of an external force is called

the _________________________________

5. Resonance is the phenomenon when the oscillating system is made _____________________________________

___________________________________________________________________________________________

6. The resonating system oscillates at _________________________________________


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Example

1. A boy is holding one end of a string with its other end tied to a pole. He shakes his hand up and down trough a

distance of 18 cm in a time of 0.20 s. The distance between two successive crests on the wave produced is 32 cm.

What is the

a) amplitude

b) frequency

c) wave speed on the string

2. Sea wave are striking the shore at a velocity of 6.0 m s-1

. The total distance of five crests on the sea waves is 4.5

m. What is the frequency of the sea waves?

3. Figure 3 shows a displacement-distance graph of a wave. Find

a) the amplitude

b) the wavelength of the wave


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4. The figure below is the displacement-time graph of wave:

Calculate

a) the amplitude

b) the frequency

c) the wavelength, if the speed of the wave is 8 cm s-1

5. The figure shows the form of a transverse wave produced by a slinky spring.

What is,

a) its amplitude

b) its wavelength

6. (a) Mark on the graph

(i) the direction of vibration of the particles and the direction of wave propagation .

(ii) two points vibrate in phase.

(b) Give one example of the transverse wave.

___________________________________

(c) Determine

(i) the amplitude

(ii) the wavelength

(d) What is the speed of the wave when the frequency is 25 Hz?


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1.2 ANALYSING REFRLECTION OF WAVES

Reflection of Water Waves

1. Reflection of a wave occurs when a wave strikes on obstacle. The wave undergoes a change in direction of

propagation when it is reflected.

Figure 6.2.1

2. Laws of reflection are:

(a) __________________________________________________________________

(b) __________________________________________________________________

3. The phenomenon of water (reflection) can be investigated using ripple tank.

Figure 6.2.2

- The water waves are produced by a vibrating bar on the water surface.

- The water acts as a lens to produce a pattern of bright and dark region on a piece of paper placed under the tank

when light passes through it. Complete the diagram below.


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Figure 6.2.3

4. The bright and dark region of the wave pattern formed on the screen because the surface of water acts as lenses.

The crest of water waves similar with ___________ and the trough of water waves similar with

________________

5. In reflection of waves, the speed (v), wavelength (λ) and frequency (f) of the wave ___________. However, the

_________________________ and ______________ of the reflected waves change.

6. The diagrams below show the pattern for the reflection of water waves. Complete the diagram below.

Figure 6.2.4


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7. Complete the diagram below.

Figure 6.2.5 Figure 6.2.6

Reflection of Sound Waves

Figure 6.2.7

1. The reflection of sound waves also obeys the reflection law.

2. The angle of reflection, r is equal to the angle of incidence, i.

3. The ___________________ and the _________________ of the incident and reflected waves __________,

hence the _________________ of the reflected waves is the same as that of the incident waves.

4. The direction of the propagation of waves changes after undergoing reflection.


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1.3 ANALYSING REFRACTION OF WAVES

1. As sea waves approach shallow water near the beach, their wavefronts become closer and closer.

2. This shows that the sea waves are approaching the beach with decreasing velocity.

3. The water waves also change their direction during their propagation through the shallow region.

4. Refraction of waves is the change in direction of propagation caused by a _____________________________

_________________________________________________________________________________________

5. After refraction, the wave has the _________________ but a _____________ __________________________

6. When a water wave transmitted from deep water into shallow water, the wave is _____________________

_________________________________________

7. When a water wave transmitted from shallow water into deep water, the wave is _____________________

_________________________________________

8. The phenomenon of water (reflection) can be investigated using ripple tank as shown below,

Figure 6.2.8

- A Perspex plate in the shape of trapezium, as

shown in figure above is placed in the centre

of the tank to create an area of shallow water

in the tank.

- Wooden bar is used to produce plane waves.

- The direction of the water waves in the areas

of deep and shallow water are observed with a

stroboscope.


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9. On each of the following diagram, draw the refracted wave by the perspex.

Rectangular plate

Trapezium shaped plate

Triangular plate

Convex lens-shaped plate

Concave lens-shaped plate


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10. The relationship between v and λ of a water wave in deep and shallow water can be obtained from the formula

v = fλ

Where frequency, f is constant in both regions.

Exercise 6.2

1. The diagram shows the stationery pattern of plane waves seen through a stroboscope with 6 slits rotating at a

frequency of 5 Hz. What is

(a) the wavelength of the water wave?

(b) the speed of the water wave?

2. Figure 1 shows water ripples in two areas of water with different depths. The observation is made with a

stroboscope with 3 slits. The frequency of the stroboscope is 4 rotations per second.

Calculate

(a) the frequency of the dipper area

(b) the wave length in the deep area and in the

shallow area

(c) the speeds of the waves in the two areas.


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3. In the following figure, ABCD is an area of deep water. Plane waves with a velocity of 2 m s-1

propagate from a

shallow area to a deeper area.

What is the frequency and speed in the area ABCD?

4. The diagram below shows water ripples crossing the boundary between deep and shallow region. The frequency

and wavelength of the incident water waves are 8.0 Hz and 2.0 cm respectively. The speed of the water waves in

the shallow region is 11.0 cms-1.

(a) Calculate the speed of the incident waves

(b) What is the frequency of the refracted

waves?

5. The following figure shows water waves from the sea

advancing towards a bay and a cape.

(a) Why area the speed and wavelength of waves in the

middle of the sea almost uniform?

The depth of water in the middle of the sea is almost

uniform.

(b) Why do the distances between the wavefronts

decrease as the waves approach the beach?

On approaching the beach, the depth of water

decreases. The speed of waves decrease and the

.

(c) Why is the water in the bay stationery compared to

the water at the cape?


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Refraction of Light Waves

Figure 6.2.9

1. When a ray propagates from one medium to an optically denser medium, the ray refracts __________ the normal.

2. The speed of light ________________ as it propagates in the glass block, causing it to alter the direction of

propagation.

Refraction of Sound Waves

1. Sound waves travel faster in _________ air than in

_________ air.

2. On a hot day, the hot surface of the Earth causes the layer

of air near the surface to be _________. This causes

sound waves to be _______________ away from the

Earth.

3. On a cool night, the sound waves travel ____________ in

the cooler layer of air near the surface of the Earth than in

the upper, warmer air. The waves are

______________________ the Earth. Hence, sound can

be heard over a longer distance on a cold night compared

with a hot day.

Figure 6.2.10


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1.4 ANALYSING DIFFRACTION OF WAVES

Diffraction of Water Wave

1. Figure 6.2.11 shows the behaviour of water waves moving into a

harbour through a narrow opening. The pattern of the water waves is

seen to be changing from plane to circular.

2. After entering the harbour, the distance between the wavefronts, i.e

their wavelength remains unchanged. However, the water waves are

spread out behind the narrow opening.

3. The phenomenon ___________________________

_________________________________________ is known as

diffraction.

4. Diffraction of waves is a phenomenon in which waves spread out as

they pass through an aperture (opening) or small obstacle.

5. Characteristics of diffracted waves:

(a) _______________________________________________________

(b) _______________________________________________________

6. The phenomenon of water (diffraction) can be investigated using ripple tank as shown below,

Figure 6.2.12

- Two pieces of metal bars are positioned to

from a slit of width 10 cm at a distance of

5 cm from the vibrating wooden bar.

- The pattern of the waves before and after

passing the slit is observed and drawn

7. Figure above shows the observation of the diffraction when water wave passes through the slit.


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If λ < a, the effect of diffraction is not obvious.

The waves are bent only at the edges after passing the

slit.

If λ ≥ a, the effect of diffraction is very obvious.

The waves are circular and appear to originate from

the small slit.

The effect of diffraction is not noticeable. The effect of diffraction is obvious. The waves

recombine after passing the obstacle.

8. At a higher frequency, the wavelength of the water wave is ____________. If λ < a, the effect of diffraction

______________________.

9. At a lower frequency, the wavelength of the water wave is _____________. If λ ≥ a, the effects of diffraction

______________________.

Diffraction of Light Wave

1. The diffraction of light waves occur when the light waves pass through a small slit or small pin hole.

Figure 6.2.14


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2. Figure above shows the diagram to observe the diffraction of light wave.

(a) a laser beam is directed through the adjustable single-slit onto the screen.

(b) the distance and the positions of the laser pointer and single-slit are adjusted until a clear diffraction pattern

of light from the laser beam fall on the screen.

(c) the width of the single-slit is adjusted and the pattern on the screen is observed for different widths of the

slit.

3. The patterns formed by the slits are as shown in figure 6.2.16

Narrow slit Wide slit

4. Diffraction pattern becomes less distinct when the slit or hole becomes wider.

5. Diffraction of light is hardly noticeable compared with diffraction of sound waves and water waves because the

wavelength of light is ___________________ (approximately 10-7

m).

6. Light waves will be diffracted if:

(a) light is propagated through a pin hole or a tiny slit where _____________________________________.

(b) the light source must be _________________ (light of one colour and therefore of one wavelength only)

7. Monochromatic light can be produced from visible light using _________________.

8. Sound waves are more easily diffracted in comparison to light waves because the wavelength of sound waves

_______________________ than the wavelength of light waves.

Diffraction of Sound Waves

1. The music from the cassette player can be heard although it is blocked by the corner of the building. This shows

that diffraction of sound waves has occurred.

2. Diffraction of sound wave occurs when there is a spreading out of waves when the waves move through a gap or

round an obstacle.


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3. The wavelength, frequency and speed of the diffracted waves are the same as the incident waves.

4. However due to the spreading of the waves, the energy per unit area of the diffracted waves is less than the

incident waves. Hence the amplitude of the diffracted waves is smaller than the incident waves.

6.5 ANALYSING INTERFERENCE WAVE

1. When two separate waves with the same frequency meet and overlap, they undergoing superposition and the

phenomenon produced known as ___________________________.

2. Interference is the __________________________________________________________________________

_________________________________________________________________________________________

3. Sources which are coherent produced waves of the same _____________, same _________________ and in same

phase.

4. There are two types of interference :

(i) ___________________________________

(ii) ___________________________________

5. The principle of superposition states that

___________________________________________________________________________________________

_______________________________________________________________________________________

6. Constructive interference occurs when

_________________________________________________________________________________________

7.

+

=

Superposition of two crests

+

=

Superposition of two trough


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8. Destructive interference occurs when

_________________________________________________________________________________________

+

=

Superposition of a crest and trough

Interference of Water Waves

Figure 2

- A ripple tank is set up with two spherical dippers in contact with the surface of the water.

- The electric motor is switched on and the pattern of the interference of the waves is observed with a stroboscope.

- Figure 2 show the result of the interference.


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Complete the result of interference above

KEY:

� Crest meet crest / Trough meet trough

� Crest meet Trough

----------- Antinode line

_______ Node line

1. A ______________ is a point where _________________________ occurs, whereas a _______ is appoint where

__________________________ occurs.

2. From the interference pattern, the distance of separation, x between two successive antinodes line and node line

depends on;

(a) ________________________________________________________

(b) ________________________________________________________

(c) ________________________________________________________

The relationship between x, λ, a and D is given by the formula,


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Interference of Light Waves

Figure 4

1. Figure 4 above shows the diagram to study the interference of light wave.

(a) a laser beam is directed trough the double-slit onto the screen. (double-slit act as coherent sources)

(b) the distance and the positions of the laser pointer and double-slit are adjusted until a clear interference

pattern of light from the laser beam fall on the screen.

2. The interference pattern observed which consist of bright fringes and dark fringes correspond to the constructive

and destructive interference respectively.

Figure 5

3. This experiment is known as ______________________________ experiment.

4. The wavelength of a light wave is given by the formula, λ = D

ax

Where,

a = __________________________________________________________

x = __________________________________________________________

D = __________________________________________________________


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Example 1

Figure 6

1. Figure 1 show the interference pattern formed on a screen in a Young’s double-slit experiment using a blue light.

The distance between the screen and the double-slit is 3.0 m. The distance between the slits is 0.3 mm.

(a) calculate the wavelength of the blue light

(b) If the blue light is replaced with a green light with a wavelength of 5.4 x 10-7

m, how many green fringes

will be observed in 27 mm?

Solution

Example 2

1. In a Young’s double-slit experiment, a white light source and a double-slit of separation 0.4 mm are used. The

distance of the screen from the double-slit is 1.7 m. The separation between 10 successive right fringes is 2.0

cm. calculate the wavelength for the white light


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Interference of Sound Waves

Figure 7

1. The figure above is used to study the interference of sound waves.

2. A few students are walk along the line between the two speakers. They are required to detect alternate regions of

loud (L) and soft (S) sound.

3. Interference is the superposition of two waves originating from two coherent sources. Sources which are

coherent produced waves of the ________________, ________________ and _____________________

4. Coherent sources of sound can be produced by two speakers connected to the same audio signal generator.

5. A loud sound corresponds to the occurrence of ______________________

6. A weak sound corresponds to the occurrence of ______________________

7. The wavelength of a sound wave is given by the formula, λ = D

ax

Where,

a = distance between the two loudspeakers.

x = distance between consecutive loud or soft sounds.

D = distance between the straight path and the loudspeakers.

Example 1

In an experiment on the interference of waves, two loudspeakers are placed at a distance of 1.5 m from each other.

They are connected to an audio signal generator to produced coherent sound waves at a frequency of 0.5 kHz.

Calculate

(a) the wavelength of the sound wave if the speed of sound is 300 m s-1

.

(b) the distance between two consecutive soft sounds at a perpendicular distance of 5 m from the source of the

sound.

Solution


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Example 2

Two loudspeakers placed 1.5 m apart, are connected to an audio signal generator adjusted to a frequency of 600 Hz.

When a student walks at a distance 0f 3.0 m in front of the loudspeakers, he hears 4 consecutive loud sounds at a

distance of 3.3 m.

(a) Calculate the wavelength of the sound waves.

(b) Calculate the speed of the sound waves in air.

Solution


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6.6 ANALYSING SOUND WAVES

1. Sound waves are longitudinal waves which require a medium for its propagation.

2. The ________ of sound waves depends on its ______________. The _____ the sound, the ________ is its

__________.

3. The __________ of sound waves depends on its _______. The _______ the pitch of the sound, the ________ is

its ____________

4. Figure below shows the relationships between amplitude and loudness of sound and frequency and pitch of

sound.

Application of Sounds Waves

1. Sound waves generated between 20 Hz and 20 kHz can be heard by normal human ears and are known as audio

waves.

2. Sound waves below 20 Hz are called infrasound and those above 20 kHz are known as ultrasound.

3. A bat can navigate in darkness by emitting very high-pitched sound waves in the ultrasonic range.

4. Dolphins use ultrasonic frequency of about 150 kHz for communication and navigation.


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5. Ultrasonic wave is used to the process of detecting cracks of flows inside a block of metal using the echo-

sounding method.

6. Sonar (Sound Navigation and Ranging) in ships use ultrasonic echoes to detect underwater objects or to determine

the depth of the water. The depth of sea water can be calculated using the formula:

7. Ultrasonic imaging is a save technique for diagnostic procedure. It is safer to use than X-ray. This technique

enables doctors to evaluate structural aspects of the organ inside the body as well as the fetus of a pregnant

mother.

8. Opticians and goldsmiths use ultrasonic cleaner to clean spectacles, jewellery and ornaments. The water used for

the cleaning purpose is vibrated by ultrasound. The vibrations shake off dirt attached to these objects.

Example 1

An ultrasonic is used to determine the depth of a seabed. A pulse of ultrasound is generated and travels to the

seabed and reflected by it. The time taken by a pulse of ultrasonic wave to travel to and fro the seabed is 0.28 s. If

the speed of sound in the water is 1500 ms-1, calculate the depth of the seabed.

Solution

Example 2

Ali shouts in front of mountain and hears his echo 4.5 seconds later. If the mountain is 765 m from Ali, calculate

the speed of sound in air.

Solution

2d = v x t


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Example 3

A microphone is connected to a cathode-ray oscilloscope. Three types of sound waves are received by the microphone.

Three types of sound waves are received by the microphone. The wave forms A, B and C displayed on the screen of

the CRO was obtained as shown in the diagram below.

(a) Which wave form represents a sound wave of large magnitude? Explain your answer

_______________________________________________________________________________________

(b) Which wave form shows a sound wave with the lowest pitch? Explain your answer.

_______________________________________________________________________________________

Example 4

A student is standing at a distance of 45 m from a wall. He gives a loud clap and the echo is heard after 0.3 s.

Calculate the speed of sound in air.

Example 5

A student is standing two high walls at a distance of 400 m and 150 m from each wall. The student gives a loud

scream.

Calculate the time interval between the two echoes he hears if the speed of sound in air is 300 m s-1.


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6.7 ELECTROMAGNETIC WAVES

Electromagnetic Spectrum

1. When you watch television, listen to the radio or cook something in a microwave oven, you are using

electromagnetic waves.

2. These waves are transverse waves and have electrical and magnetic components.

3. The components oscillate at right angles to each other and to the direction of propagation as shown below;

4. Electromagnetic wave carries ____________ but do not require _______________


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5. The electromagnetic spectrum consists of a group of waves with similar natures. The members of the

electromagnetic spectrum arranged in increasing frequencies and decreasing wavelengths are radio waves,

microwaves, infrared rays, visible light, ultraviolet rays, X-rays and gamma rays.

Electromagnetic spectrum

6. Table 1 list out the sources, characteristics and applications of the electromagnetic spectrum.

Type and wavelengths Sources Applications

Radio waves

λ: 10-1

– 103 m

- Radio

- Television transmitter

- For broadcasting and wireless

communication.

- UHF (Ultra high frequency) radio waves –

television and hand phones.

- VHF (Very high frequency) radio waves –

local rdio and wireless communication used

by the police.

Microwaves

λ: 10-1 – 10-3 m

- Radar transmitter

- Microwaves oven

- Communication system with satellites.

- Used in radar system

- Global Positioning System (GPS)

- For cooking – microwaves oven.

Infrared rays

λ: 10-3 – 10-6 m

- Warm or hot objects

- The sun

- For cooking food – ovens, grills and

toasters.

- Remote controls for televisions and video

players.

- Intruder alarm system

- Night vision


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Visible light

λ: 4 x 10-7 – 8 x 10-7 m

- The sun

- Hot objects

- Electric bulbs

- Fire

- LED

- Photography

- Photosynthesis by plants

- Enable human beings and animals to see.

Ultraviolet rays

λ: 10-6 – 10-9 m

- The sun

- Mercury lamps

- Very hot objects

- Fluorescent lamp

- Detection of security markings in currency

notes

- Production of fluorescent effects.

- Sterilisation of surgical tools and plant

seedlings

X-rays

λ: 10-8 – 10-12 m

- X-ray tubes

- Outer space

- Help doctors to check bones and teeth.

- Help engineers to check welds and metal

joints

- Detection of cracks in building structure.

- Radiotherapy

Gamma rays

λ: 10-12

- Radioactive

substances

- Cosmic rays

- Cancer treatment

- Sterilisation of surgical tools and food

- Pest control in agriculture

Prepared by:

En. Adnan Shamsudin

(Dip Sc, BSc, Dip Edu)

Head of Physics Department

SMK Sultan Ismail, Johor Bahru.

waves chapter 1 form 5

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