1.1 Gelombang - SPM - Fizik -Tingkatan 5

Chapter 1: Waves

1.1 Understanding Waves

Motion of Waves

• 1 An oscillating or vibrating motion in which

a point or body moves back and forth along a

line about a fixed central point produces

waves.

Motion of Waves

• 2. Examples of waves:

• (a) Light waves are produced as a result

of vibrations of electrons in an atom.

Motion of Waves

• 2. Examples of waves:

• (b)Sound waves are produced by

vibrating mechanical bodies such as

guitar strings or a tuning fork.

Motion of Waves

• 2. Examples of waves:

• (c) Water waves are produced by

disturbance (or vibration) on a still water

surface.

Propagation (Traveling) of Waves

• 1.When a wave travels through a

medium, the particles of the medium

vibrate about their equilibrium

positions.

Direction of

waves

Propagation (Traveling) of Waves

• 2.However, the particles of the medium

do not travel in the direction of the

wave.

Propagation (Traveling) of Waves

• 3 A wave transfers energy and the

momentum from the source of the wave

(the oscillating or vibrating system) to the

surroundings.

Propagation (Traveling) of Waves

• Activity 1.1: To demonstrate that waves transfer

energy without transferring matter

• Apparatus:

• Radio, candle and matches.

Propagation (Traveling) of Waves

• Activity 1.1: To demonstrate that waves transfer energy without transferring matter

• Procedure

• 1. A candle is placed about 10 cm from the speaker of a radio.

Propagation (Traveling) of Waves

• Procedure

• 2. The candle is lit and the movements of its flame is observed.

Propagation (Traveling) of Waves

• Procedure

• 3. Then, the radio is turned on and the volume of the sound is gradually increased until a change in the movement of the flame becomes noticeable.

Propagation (Traveling) of Waves

• Discussion

• 1. The flame vibrates when the radio is turned on.

Propagation (Traveling) of Waves

• Discussion

• 2. This observation shows that the propagation of the sound waves from the vibration of the cone of the speaker transfers energy (or momentum) to the flame and causes it to vibrate.

Propagation (Traveling) of Waves

• Conclusion

• Waves transfer energy from a vibrating

system without transferring matter.

Wavefronts

• 1. A wave front is a line or plane on

which the vibrations of every points on it

are in phase and are at the same

distance from the source of the wave.

Same

Phase

Wavefronts

• 2 . Points in a wave are in phase if they

vibrate in the same direction with the

same displacement.

Same

displacement

Plane Wave fronts

• 1 . Figure 1.3 shows the production of

plane water waves when a wooden bar

vibrates vertically at a constant frequency

on the surface of the water.

Plane Wave fronts

• 2. Lines PQ, RS, TU and VW are straight

lines along the respective crests of the

waves. These lines are called wave

fronts.

Circular Wave fronts

• 1. When we use a fingertip to touch the

surface of water repeatedly, circular wave

fronts are produced as shown in Figure

1.4.

Types of Waves

• There are two types of waves.

• (a) Transverse wave

• (b) Longitudinal wave

Transverse Waves

• 1. A transverse wave is a wave in which

the vibration of particles in the medium is

at right angle (perpendicular) to the

direction of propagation of the wave.

Transverse Waves

• 2. A model of a transverse wave can be

produced by a slinky spring as shown in

Figure 1.6.

Transverse Waves

• 3. Examples of transverse waves are

water waves and light waves.

Longitudinal Waves

• 1. A longitudinal wave is a wave in which

the vibration of particles in the medium is

parallel to the direction of propagation of

the wave.

Longitudinal Waves

• 2. 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 in

Figure 1.8.

Longitudinal Waves

• 3 . Example of longitudinal waves is

sound waves.

Amplitude, Period and Frequency of a Wave

• 1 . The amplitude, A, of a vibrating system is

maximum displacement from its equilibrium position.

It is a measure of height of the wave crest or depth of the

wave trough.

Amplitude

Amplitude, Period and Frequency of a Wave

• 2 . In Figures 1.9 (a) and (b), the distance OQ is the

amplitude, where O is the equilibrium position of the

vibrating system.

Amplitude

Amplitude, Period and Frequency of a Wave

• 3 . The period, T, of a vibrating system is the time

taken to complete an oscillation.

Period

Amplitude, Period and Frequency of a Wave

• 4. In the two vibrating (oscillating) systems show in

Figure 1.9, a complete oscillation are:

• (a) from P Q P or Q P Q,

• (b) from OPQO or

OQPO

Amplitude, Period and Frequency of a Wave

• 5. If a vibrating system makes n complete

oscillations in a time of t seconds, the

period of oscillation, T of the system is

second

• The SI unit of period is second.

n

t

Amplitude, Period and Frequency

of a Wave

• 6 The frequency, f, is the number of complete

oscillations made by a vibrating system in one second.

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

Amplitude, Period and Frequency

of a Wave• 7 From the formulae of T and f, the relationship

between period, T and frequency, f is:

• T is inversely proportional to f and vice versa.

Amplitude, Period and Frequency

of a Wave

• Example 1:

• In an experiment, Aziz observes that a simple pendulum

completes 30 oscillations in 48.0 seconds. What is

• (a) the period of oscillation?

• (b) the frequency of oscillation?

Amplitude, Period and Frequency

of a Wave

• Example 1:

• Solution

• (a)

s6.130

48.0

oscllation completed ofnumber

takentimeTperiod,

Amplitude, Period and Frequency

of a Wave

• Example 1:

• Solution

• (b)

Hz625.06.1

1

T

1ffrequency,

Displacement-time Graph of a

Wave

• 1. The sinusoidal graph in Figure 1.10 is a

graph of displacement, s against time, t of

a load on a spring.

Displacement-time Graph of a

Wave

• 2 From the graph of s against t in Figure 1.10, the

following information is obtained.

• (a) Amplitude, A = a cm

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

• (i) O and F, (ii) C and G or (iii) P and Q.

Displacement-time Graph of a

Wave

• Example 2:

• Figure 1.11 shows the displacement-time graph of the

oscillation of a mass on a spring.

• Figure 1.11

Displacement-time Graph of a

Wave

• Example 2:

• From the graph,

• (a) state the amplitude,

• (b) calculate the period of the oscillation,

• (c) calculate the frequency of the oscillation.

Displacement-time Graph of a

Wave

• Example 2:

• Solution

• (a) Amplitude, A = 5 cm

•

• Example 2:

• Solution

• (b) Period of oscillation, T = 0.04 s

• Example 2:

• Solution

• (c) Frequency of oscillation,

HzT

f 2504.0

11

Displacement-distance Graph of a

Wave

• 1. Figures 1.12 (a) and (b) show the

propagation of a water wave and a sound

wave.

Displacement-distance Graph of a

Wave

R: Rarefaction

C:Compression

Displacement-distance Graph of a

Wave

• 2. The displacement, s of each particle of the medium

at different distances can be shown in a displacement-

distance graph as shown in Figure 1.12 (c).

Displacement-distance Graph of a

Wave

• 3. The wavelength, , is the distance between

successive points of the same phase in a wave.

Displacement-distance Graph of a

Wave

• For example:• (a) the distance between two successive crests or two

successive troughs in a water wave,

Displacement-distance Graph of a

Wave• (b) the distance between two successive compressions

or two successive rarefactions in a sound wave.

The SI unit of wavelength, , is metre (m).

Displacement-distance Graph of a

Wave• Example 3:

• Figure 1.13 shows a displacement-distance graph of a wave.

• Figure 1.13

• Find

• (a) the amplitude,

• (b) the wavelength of the wave.

Displacement-distance Graph of a

Wave• Example 3:

• Solution

• (a) Amplitude, A = 4 cm

•

Displacement-distance Graph of a

Wave• Example 3:

• Solution

• (b) Wavelength, =12 cm

Relationship between Speed (v),

wavelength, and Frequency (f)

• The relationship between speed,

wavelength and frequency can be

obtained by relating the SI unit of the

quantities.

fv

Relationship between Speed (v),

wavelength, and Frequency (f)

• Example 4:

• A wave of frequency 120 Hz has a

wavelength of 5.0 m. What is the speed of

the wave?

Relationship between Speed (v),

wavelength, and Frequency (f)

• Example 4:

• A wave of frequency 120 Hz has a

wavelength of 5.0 m. What is the speed of

the wave?

Solution

f = 120 Hz and =5.0m

Speed of wave,

v = f

= 120 x 5

= 600 m s-1

Relationship between Speed (v),

wavelength, and Frequency (f)

• Example 5:

• The displacement-distance graph in Figure

1.14 shows the motion of a transverse

wave. The source of the wave produces

10 complete waves in one second.

• Figure 1.14

Relationship between Speed (v), wavelength,

and Frequency (f)

• Example 5:

• Calculate

• (a) the amplitude,

• (b) the wavelength, and

• (c) the speed of the wave.

Relationship between Speed (v),

wavelength, and Frequency (f)

• Example 5:

• Solution

• (a) Amplitude, A = 6 cm

•

Relationship between Speed (v),

wavelength, and Frequency (f)

• Example 5:

• Solution

• (b) Wavelength, = 20 cm

•

•

•

1o 2o

Relationship between Speed (v),

wavelength, and Frequency (f)

• Example 5:

• Solution

• (c) Frequency, f = 10 Hz, = 20 cm

• Speed, v = f

=10x20

• = 200 cm s-1