Reflection of Waves

7/29/2019 Reflection of Waves

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8/12/13 Reflection of waves

www.oocities.org/wave032002/reflection.htm

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.

[Online quiz]

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Reflection of Waves

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