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Representing waves
1. Representing waves
2. Representing waves
There are two ways we can represent awave in a graph;
3. Displacement/time graph
This looks at the movement of one point ofthe wave over a period of time
displacement
cm
1
0.1
-1
-2
0.2
0.3
0.4
Time s
4. Displacement/time graph
This looks at the movement of one point ofthe wave over a period of time
displacement
cm
1
PERIOD
0.1
-1
-2
0.2
0.3
0.4
Time s
5. Displacement/time graph
This looks at the movement of one point ofthe wave over a period of time
displacement
cm
1
PERIOD
0.1
-1
-2
0.2
0.3
0.4
Time s
6. Displacement/time graph
This looks at the movement of one point ofthe wave over a period of time
displacement
cm
1
PERIOD
0.1
-1
-2
0.2
0.3
0.4
Time s
IMPORTANT
NOTE: This
wave could be
either transverse
or longitudnal
7. Displacement/distance graph
This is a “snapshot” of the wave at aparticular moment
displacement
cm
1
0.4
-1
-2
0.8
1.2
1.6
Distance cm
8. Displacement/distance graph
This is a “snapshot” of the wave at aparticular moment
displacement
cm
1
WAVELENGTH
0.4
-1
-2
0.8
1.2
1.6
Distance cm
9. Displacement/distance graph
This is a “snapshot” of the wave at aparticular moment
displacement
cm
1
WAVELENGTH
0.4
-1
-2
0.8
1.2
1.6
Distance cm
10. Displacement/distance graph
This is a “snapshot” of the wave at aparticular moment
displacement
cm
1
WAVELENGTH
0.4
-1
-2
0.8
1.2
1.6
Distance cm
IMPORTANT
NOTE: This
wave could also
be either
transverse or
longitudnal
11. Wave intensity
12. Wave intensity
This is defined as the amount of energy perunit time flowing through unit area
It is normally measured in W.m-2
13. Wave intensity
For example, imaginea window with an
area of 1m2. If one
joule of light energy
flows through that
window every second
we say the light
intensity is 1 W.m-2.
14. Intensity at a distance from a light source
I = P/4πd2where d is the distance from the light source
(in m) and P is the power of the light
source(in W)
15. Intensity at a distance from a light source
I=2
P/4πd
d
16. Sound intensity
The lowest intensity that can normally beheard by a human ear is 1 x 10-12 W.m-2
This is a sound intensity level of 0 dB
17. Intensity and amplitude
18. Intensity and amplitude
The intensity of a wave is proportional tothe square of its amplitude
I α a2
(or I =
2
ka )
19. Intensity and amplitude
This means if you double the amplitude of a wave,its intensity quadruples!
I=
2
ka
If amplitude = 2a,
new intensity = k(2a)2
new intensity = 4ka2