reflection of waves
TRANSCRIPT
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Reflection of waves
Reflection of wave takes place when a wave strike an obstacle. The wave will change its direction of propagation when it is reflected.
Characteristics of Reflection of waves:
1. It obeys the Law of Reflection.
2. The wavelength, of the reflected wave is the same as that of the incident waves.
3. The frequency,f of the reflected waves is the same as that of the incident waves.
4. Therefore the speed, v of the reflected waves is the same as that of the incident waves.
The phenomenon of reflection of waves obeys the Laws of reflection:
i. the incident wave, the reflected wave and the Normal lie in the same plane which is perpendicular to
the reflecting surface at the point of incident.
ii. The angle of incident, i is equal to the angle of reflection, r.
Angle of Reflection= Angle of Incidence
Angles are measured withrespect to the normal line
(the perpendicular line).
Reflection of water waves
The phenomenon of reflection of water waves can be investigated using a ripple tank. The water waves are produced by a vibrating
source on the water surface.
A horizontal bar will produced a plane wave. While a round source will produce circular wave
Wavelength of a circular wave.
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Study more about water wave here.
Video clips on ripple tank
Virtual lab on wave
Being a transverse wave, the crest of the water wave acts as a convex lens that converge the light ray and produced a bright area on the white paper. While the
trough acts a concave lens that diverge light ray and produced a dark area on the white paper. Hence a series of bright and dark regions are produced on the
white paper. A mechanical stroboscope is used to observed the pattern of the reflected waves. The moving waves will appear to be stationary when the
frequency of the stroboscope is the same as the frequency of the water waves. The frequency of the stroboscope = np, where n = the number of slits on the
stroboscope and p = the frequency of rotation of the stroboscope (the number of the stroboscope is turned in a second). View some photographs taken by
stroboscopic camera.
Characteristics of reflection of wave:
1. angle of reflection = angle of incidence
2. wavelength, frequency and speed of the wave do not change after reflection.
3. direction of propagation and velocity of wave changes.
Video clips on:
Reflection of plane wave on a plane reflector Reflection of circular wave on a plane reflector
Reflection of plane wave on a circular reflector
Reflection of light waves
Reflection of light on a Plain mirror
Light rays from an object strike the surface of a plane mirror. The rays are reflect
appear to come from behind the mirror. The reflected rays are drawn as if they ar
image is virtual. Therefore the rays behind the mirror do not exist. They are virtua
represented by dotted lines. The continuous lines from the mirror to the eye indica
The distance between the object and the mirror is the same as the distance betwe
mirror.
Characteristics of the image of a plane mirror:
1. Virtual
2. Same size as the object
3. laterally inverted
Application of reflection of light on plane mirror
Defence & safety Telecommunication
1. A periscope is an optical instrument used to view objects beyond obstacles. Light waves
from an object which is incident on a plane mirror in the periscope are reflected twice
before entering the eyes of the observer.
2. The rear view mirror and side mirror in a car are used to view cars behind and at the side
while overtaking another car or making a turn. The mirrors reflect light waves from the cars
and objects into the driver's eye.
3. The lamp of a car emit light waves with minimum dispersion. The light bulb is placed at the
focal point of the parabolic reflector of the car lamp so that the reflected light waves are
parallel to the principal axis of the reflector. Parallel light waves have a further coverage
(shines further).
1. Optical fibres have many advantages compared to conventional cables in t
information. Optical fibres are light, flexible, electrically non-conducting an
information.
2. Infrared waves from a remote control of electrical equipment (TV / Radio)
the surroundings and received by the TV or radio.
http://www.oocities.org/wave032002/reflection3.asfhttp://www.oocities.org/wave032002/reflectioncircular.asfhttp://www.oocities.org/wave032002/reflection1.asfhttp://d/MIT/websites/Physics%20Fm4/stroboscope/ABM/More%20High%20Speed%20and%20Photoinstrumentation%20Photography.htmhttp://d/MIT/websites/Physics%20Fm4/stroboscope/ABM/digital%20stroboscopic%20camera.htmhttp://www.falstad.com/wavebox/http://www.oocities.org/wave032002/watertank1.asfhttp://www.oocities.org/wave032002/Ripple_tank.htm -
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Reflection of a curved mirror
If a concave mirror is thought of as being a slice of a
sphere, then there would be a line passing through the
center of the sphere and attaching to the mirror in the
exact center of the mirror. This line is known as the
principal axis. The point in the center of the sphere
from which the mirror was sliced is known as the
center of curvature and is denoted by the letterC in
the diagram below. The point on the mirror's surface
where the principal axis meets the mirror is known as
the vertex and is denoted by the letterA in the diagram
below. The vertex is the geometric center of the mirror.
Midway between the vertex and the center of curvature
is a point known as the focal point; the focal point is
denoted by the letterF in the diagram below. The
distance from the vertex to the center of curvature is
known as the radius of curvature (represented by R).
The radius of curvature is the radius of the sphere fromwhich the mirror was cut. Finally, the distance from the
mirror to the focal point is known as the focal length
(represented by f). Since the focal point is the midpoint
of the line segment adjoining the vertex and the center of
curvature, the focal length would be one-half the radius
of curvature.
Concave mirror Characteristics of
image
1. Light rays from very far object are parallel. A real image is formed at the Principle
Focus.
Real
formed at
Principle
Focus
2. Object placed > 2f
Real
Diminished
Inverted
3. Object placed at 2f
Real
same size
as the
object
Inverted
Rules of reflection of curved mirror
1. Incident light rays that is parallel to the principle
axis is reflected towards the point Principle
Focus, F.
2. Any light ray that passes through the Principle
Focus, F is reflected parallel to the principle axis.
3. Image is form at the point of intersection of 2
reflected rays.
Look at the animation below.
4. Object placed between f and 2f
Real
Diminished
in size
Inverted
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5. Object placed at F
Image is formed
at infinity
6. Object is placed < f. Virtual
MagnifiedUpright
At this position,
concave mirror
acts as a
magnifying
mirror.
Convex mirrorImage is always
virtual,diminished,
upright
irrespective of
where the object
is placed.
Application of Reflection of a curved mirror
Convex Mirror Concave Mirror
The image of a
convex mirror is
always Virtual,
Diminished,
upright.
The image of a concave mirror depends on the
object distance.
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A
convex
mirror
has a
wider
field of
vision
than a
plane
mirror.
Therefore it is used as a surveillance mirror and a blind
corner mirror which is placed at a sharp bend on a
road.
A concave mirror converge all parallel
light rays to a point along its principle
axis called Focal point.
A
convex mirror is used as a side mirror of a car because
it gives an upright image and a wider field of vision than
a plane mirror.
Concave mirror with long focal
lengths can be used as makeup
mirror, shaving mirror or a
dentist's mirror as they form
magnified and upright image.
A dentist mirror
The lamps of a car emit light waves with minimum
dispersion. The light bulb is placed at the focal point of the parabolic reflector of the car lamp so that
the reflected light waves are parallel to the principal axis of the reflector. Parallel light waves shine far
and have a further coverage.
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Parallel light rays reflected and focused on oil-filled pipes placed at the Principle focus of the parabolic
mirror, which collect heat, make steam, propel generator turbines.
Application of the reflection of sound waves
1. Sonar (Sound Navigation and Ranging). Sonaris used to detect underwater objects (corals /
fishes) or to determine the depth of the water by
means of an echo. Sonar equipment emits a high
frequency sound signal which is reflected by the
object in the water. The reflected sound wave is
received by the sonar receiver. The time taken
for the echo to return is used to determine the
distance of the object below the water surface.
2. The phenomenon of the reflection of sound wave is used to determine the distance between 2 objects, eg. depth of awell or width of a valley.
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3. Bat detect its prey by means of echo from sound
wave.
4. The high frequency vibrations caused by ultrasound can be used in the cleaning of small, intricate items such as spect
jewellery and small machine parts. The items are placed in a liquid bath which is vibrated by ultrasound to loosen dirt
corrosions.
5. Ultrasound is also used to clean our teeth.
6. Sonogram. Ultrasound scanning is used widely in the medical field to check the development of foetuses in pregnant
women or to detect cancerous growth in a patient's body. Ultrasound produced by a transducer probe is sent into a
patient's body. The reflected ultrasound from the foetuses is detected again by the transducer. The transducer relays
received signal to a computer to form an image of foetuses on a screen.
Ancient theater is circular.
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