1. 2 REFLECTION OF WAVES
NURUL FADHILAH BINTI ALIAS
MRSM KUALA KLAWANG, NEGERI SEMBILAN
What will happen to the waves after they hit the
retaining (tembok) wall?
Water waves hitting a wall
When an object, like a ball, is thrown
against a rigid wall it will…?
This "reflection" of the object
can be analyzed in terms of
momentum and energy
If the collision between ball and wall is
perfectly ELASTIC, then all the
incident energy and momentum is
reflected, and the ball bounces back
with the same speed
If the collision is INELASTIC, then the wall (or ball)
absorbs some of the incident energy and
momentum and the ball does not bounce back with the
Waves also carry energy and momentum
whenever a wave
encounters an obstacle,
they are reflected by the
reflection of waves is responsible for
echoes, radar detectors, and for allowing
standing waves which are so important
to sound production in musical
When a wave reaches a
boundary it is:
•Partially reflected (bounces off
•Partially transmitted through
Law of Reflection
Angle of incidence = Angle of reflection
Circular wave reflection from a concave
Source far from barrier
Circular wave reflection from a concave
Source near to the obstacle
Circular wave reflection from a convex
Source further from obstacle
SOURCE IS FLAT
SOURCE IS CIRCULAR
• When rays of light strike any surface the rays
are reflected , unless the surface is black, when
they are absorbed.
• The reflection depend on how smooth the
surfaces are. Good mirrors reflect well over 90%
of the light that reaches them, with only a small
amount being absorbed.
• A plane mirror is a flat smooth surface which
reflects regularly most of the light falling on it.
• The phenomenon of reflection of light obeys the
law of reflection.
(a) The angle of incidence is equal to the angle of
(b) The incident wave, the reflected wave and the normal
lie in the same plane.
• It also can be seen that
(a) The size of the image = the size of the object
(b) The distance of the image = the distance of the object
• A reflection produced by a smooth surface.
• Reflection from a rough surface.
Reflection from a Plane Mirror
(dotted lines show
Step by step to Draw image…
Please refer to the text book…
Learn and practice step by step how to draw the
Type of Image formed by a
• Laterally inverted
• Same size as the object
• Virtual and
• As far behind the mirror as
the object is in front of it
Refer pg. 133 in
your txt bk.
What is the minimum mirror
height required for a person to
see their full self in the mirror?
Curved mirrors can make things look
smaller or BIGGER.
C = center of curvature
(center of sphere of the
R = The distance between C
and the mirror is called the
radius of curvature
f = FP (FP = ½ CP)
F = Principal focus
Principal Axis = connecting
line from the centre of
curvature to point P
search-lights and vehicles headlights to get powerful
parallel beams of light.
They are often used as shaving mirrors to see a larger
image of the face.
The dentists use concave mirrors to see large images of
the teeth of patients.
Large concave mirrors are used to concentrate sunlight
to produce heat in solar furnaces.
commonly used as rear-view (wing) mirrors in
These mirrors are fitted on the sides of the
vehicle, enabling the driver to see traffic behind
him/her to facilitate safe driving.
Convex mirrors are preferred because they
always give an erect, though diminished, image.
Also, they have a wider field of view as they are
Thus, convex mirrors enable the driver to view
much large area than would be possible with a
If you were a sound engineer, what is the modification that you
have to do to improve a recording studio. In your explanations ,
include steps to overcome sound reflection problems.
You are engaged by an interior design company to help to design a
café in the town. You are required to make the café look more
spacious. Explain how to make the hall look bigger by fixing mirrors
on the wall.
Make a mind map of reflection of wave. Make sure all
important points are included. Use a manila card or a
Make a table of comparison of reflection waves of water
waves, light waves and also sound waves.
Experiments of Reflection
Aim : To observe and describe the reflection of water waves
in terms of the angle of incidence, angle of reflection and
Apparatus : ripple tank, straight dipper, straight reflector,
stroboscope, white mahjong paper, metre rule, power
1. Set up the apparatus as shown in the figure above.
2. Pour water into the ripple tank to a depth of about
1 cm and adjust the stands to ensure the depth of
the water in the tank is uniform.
3. Lower the straight dipper until it just touches the
surface of the water.
4. Place a straight reflector parallel to the dipper, 30
5. Switch on the lamp and the motor. Adjust the
frequency of the motor by sliding the rheostat so
that the image of the wave is clear.
6. Use the stroboscope to freeze the image of the
7. Mark the image on the white paper.
8. Measure the angle of incidence, angle of
reflection, wavelength of the incident waves and
9. Replace the paper, repeat steps 4 – 8 with the
angle between the reflector and the dipper at 15º,
30º ,45º and 60º.
10. Tabulate your data.
11. Deduce the relationship between
i. the angle of incidence and angle of reflection;
ii. The wavelength of the incident waves and reflected
•From the observation, the incident angle i, is equal to the
•The length of incident wave is the same as the length of
reflection wave after it is reflected
The angle of incidence, i is equal to the angle of reflection , r
A simple experiment of reflection of sound waves
Equipment and materials:
Stopwatch, 2 cardboard tube with length 50 cm, smooth wall,
1. Place a stop watch at the end of a hollow tube.
2. The tube is placed at an angle to a reflecting surface as shown in the above
3. Keep a smooth wood vertical on the table top.
4. Place another hollow tube on the other side of the smooth wood and hold it
close to ear.
5. Adjust the angle of the second tube until a loud ticking is heard.
Make a conclusion of this activity.
Appendix 2 (Sound Wave)
It is observed that the loudest ticking sound is heard when the angle of
incident is the same as the angle of reflection.
1.Soft board/wood is used to avoid the ticking sound of the stopwatch
from being heard directly by the listener’s ears.
2.Smooth wall reflects sound waves more efficiently.
The angle of incidence , i is equal to the angle of reflection , r.
Draw the pattern of reflected waves and describe its
characteristic. Make a comparison between incident waves and
reflected waves in terms of :
i. angle of incidence , i
ii. angle of reflection , r
iii. wavelength, frequency and speed
iv. direction of propagation of the wave