1.1 waves

Chapter 1: WAVES

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WAVES
1.1 Waves
1.2 Reflection of waves
1.3 Refraction of waves
1.4 Diffraction of waves
1.5 Interference of waves
1.6 Sound waves
1.7 Electromagnetic waves

Learning outcomes 1
By the end of this lesson you should
able to:
Describe what is meant by wave motion
Recognize that waves transfer energy
without transferring matter
Compare transverse and longitudinal
waves and give examples of each
state what is meant by wavefront.
State the direction of propagation of
waves in relation to wavefronts.

Throw a stone in a pool, what can you see?

Ripple spread out in an expanding circle

Wave motion
Oscillating or vibrating
motion in which a point
or body moves back and
forth along a line about a
fixed central point

Oscillating/Vibrating System

Oscillating/Vibrating system =
Source
Produces waves


Waves
Waves transfer energy
from 1 point to another
Without transferring
matter


Matter

Receiver

Source


Trail of destruction in Penang


waves

transverse longitudinal

The vibration of The vibration of the
the medium is medium is
perpendicular parallel
to the direction of to the direction of
propagation of the propagation of the
wave wave
Electromagnetic wave Sound wave

Transverse Wave


crest
trough

Lines joining all the points of the same
phase : wavefront


Wavefronts are perpendicular to the direction of
propagation of wave

Learning outcomes 2
By the end of this subtopic you should able to:
 Define amplitude, period, frequency, wavelength and
speed of wave.
 Sketch and interpret a displacement-time graph for a
wave.
 Sketch and interpret a displacement-distance graph
for a wave
 Clarify the relationship between speed, wavelength,
and frequency.
 Describe damping in an oscillating system
 Describe resonance in an oscillating system


Terms to describe wave:
Unit?
1. Wavelength
Distance between 2 adjacent points
of the same phase* on a wave
*trough & trough//crest & crest//
*compression &
compression//rarefaction &
rarefaction

Wave form, showing wavelength & amplitude


Terms to describe wave:

Unit?
2. Amplitude (a or A)
maximum displacement from its
equilibrium position


Swing of simple pendulum

Relate displacement & amplitude

3. Period
Time taken for one complete
oscillation of a wave


4. Frequency (f)
The number of complete oscillation in
one unit time

f = 1/T T = period
Frequency, f = Velocity, v
Wavelength, λ
f=v/λ

5. Wave speed
The measurement of how fast a
crest is moving from a fixed point
v = fλ


1. Displacement-time Graph
(of a particle on a wave)
Period >> time between 2
consecutive point in phase in a
graph

Amplitude
T = Period Frequency? Wavelength?

2. Displacement-distance Graph
(of a particle on a wave)


Damping in an oscillating system

Amplitude decreases
Period & frequency constant

Resonance
Resonance is a phenomenon where a
system vibrates with maximum amplitude
when the external frequency is the same
as natural frequency.
External factor’s frequency //forced
frequency
natural frequency: Every object has it’s
own frequency :

Barton’s Pendulum

A

E
B D
C

Which one has same length?
Same length, same frequency

Example of resonant system
1. Playground swing
2. Soprano
3. Music instrument : guitar,
flute…


1. Playground swing

If the `push’ is according to the swing natural
frequency, the swing will resonate.
Oscillate with maximum amplitude

2. Soprano singer breaking glass


Tacoma Narrow Bridge


Exersices


Homework
Quick Review 1.1 Page 12
Question 2 only


bar


(a) Draw the wavefront of the water wave.


(b) Explain how wavefront can
be observed on the screen
below the ripple tank.


Acts as
Concave
lens

Acts as
Convex
lens

Crest acts like convex lens: converge the light onto the
screen, produce bright pattern on the screen

QR1.1
(c) What is the difference in λ of the waves
obtained if the v of the motor increased?

From vwater wave = fλ
when vmotor increases, fmotor
increases
Hence, λ decreases
*Vwater wave depended on depth

Extra Exersices


1.1 waves

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