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6.3 Analysing Reflection Wave

Reflection of waves

Reflection of a wave occurs when a wave strikes an obstacle such as barrier, plane reflector , mirror and wall.

The reflection of waves obeys the law of reflection :

(a) The angle of incidence is equal to the angle of reflection.

(b) The incident wave, the reflected wave and the normal lie in the same plane.

When the reflection of a wave happened , the wavelength ,λ, the frequency, f and the speed , v do not change but the direction of propagation of the wave changes.

Reflection of water waves

To investigate the reflection of water waves a metallic plane reflector is placed at the centre of a ripple tank. The motor with a wooden bar attached is switched on to produce plane waves which propagate towards the reflector. The reflector repositioned to produce different angles of incidence.

The following figure shows two examples pattern of the reflection of the water waves.

(a)

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Analysis result:

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(b)

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Analysis result :

 clip_image007

The experiment to investigate the relationship between the angle of incidence and the angle of reflection of a water wave.

Hypothesis:

The angle of reflection increases as the angle of incidence increases.

Aim of the experiment :

To investigate the relationship between the angle of incidence and the angle of reflection.

Variables in the experiment:

Manipulated variable: Angle of incidence

Responding variable: Angle of reflection

Fixed variable: depth of water in ripple tank

List of apparatus and materials:

Ripple tank, lamp, motor ,wooden bar , power supply white paper , protractor ,plane reflector and mechanical stroboscope.

Arrangement of the apparatus:

clip_image009

The procedure of the experiment which include the method of controlling the manipulated variable and the method of measuring the responding variable.

The power supply is switched on to produce plane waves which propagate towards the reflector.

The incident waves and the reflected waves are freeze by a mechanical stroboscope.

The waves are sketched on the screen.

By using a protractor , the angle of incidence is measured = i and the angle of reflection = r

The experiment is repeated 5 times for the other angles of incidence.

Tabulate the data:

  i

           

   r

           

Analysis the data:

Plot the graph r against i

clip_image011

some analysis of water wave reflection with a different reflector.

clip_image002

clip_image002[5]

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clip_image012

Reflection of light waves

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 reflection.

(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

The experiment to investigate the relationship between the angle of incidence and the angle of reflection of a light wave.

Hypothesis:

The angle of reflection increases as the angle of incidence increases.

Aim of the experiment :

To investigate the relationship between the angle of incidence and the angle of reflection.

Variables in the experiment:

Manipulated variable: Angle of incidence

Responding variable: Angle of reflection

Fixed variable: position of the plane mirror

List of apparatus and materials:

Ray box, plane mirror, plasticine, protractor and white paper

Arrangement of the apparatus

clip_image013

The procedure of the experiment which include the method of controlling the manipulated variable and the method of measuring the responding variable.

A normal line ,ON is drawn on the white paper.

A ray of light from the ray box is directed to the plane mirror.

By using a protractor , the angle of incidence is measured = i and the angle of reflection = r

The experiment is repeated 5 times for the other angles of incidence.

Tabulate the data:

i

           

r

           

Analysis the data:

Plot the graph r against i

clip_image011[1]

Reflection of sound waves

The sound waves is reflected by walls and ceilings of buildings, unborn baby or sea bed.

Echo is a phenomenon when a sound wave has been reflected of a surface , and is heard after the original sound.

The experiment to investigate the relationship between the angle of incidence and the angle of reflection of a sound wave.

Hypothesis:

The angle of reflection increases as the angle of incidence increases.

Aim of the experiment :

To investigate the relationship between the angle of incidence and the angle of reflection.

Variables in the experiment:

Manipulated variable: Angle of incidence

Responding variable: Angle of reflection

Fixed variable: the position of stop watch from the smooth wall.

List of apparatus and materials:

Cardboard tube, soft wood , stop watch, protractor and smooth wall.

Arrangement of the apparatus:

clip_image015

The procedure of the experiment which include the method of controlling the manipulated variable and the method of measuring the responding variable.

By using a protractor , the angle of incidence is measured = i

The stopwatch is started.

The cardboard tube B is moved around until the watch can be heard most clearly.

By using the protractor , the angle of reflection is measured = r

The experiment is repeated 5 times for the other angles of incidence.

Tabulate the data:

i

           

r

           

Analysis the data:

Plot the graph r against i

clip_image011[2]

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