PHYSICS LAB EXPERIMENT
EXPERIMENT # 4
LAWS OF REFLECTION OF
SOUND
Our Objective
To verify the laws of
reflections of sound.
The Theory
What is reflection?
Reflection is the change
in direction of a wavefront at an interface between two different media so that
the wavefront returns into the medium from which it originated. Common examples
include the reflection of light, sound and water waves.
Do you know how sound propagates?
Sound propagates through
air as a longitudinal wave. The speed of sound is determined by the properties
of the air, and not by the frequency or amplitude of the sound. If a
sound is not absorbed or transmitted when it strikes a surface, it is
reflected. The law for reflection is the same as that of light, ie., the angle
of incidence of a sound wave equals the angle of reflection,
just as if it were produced by a 'mirror image' of the stimulus on the opposite
side of the surface.
How do we describe the reflection of sound?
When sound travels in a
given medium, it strikes the surface of another medium and bounces back in
some other direction, this phenomenon is called the reflection of sound. The
waves are called the incident and reflected sound waves.
What are incident and reflected sound waves?
The sound waves that
travel towards the reflecting surface are called the incident sound waves. The
sound waves bouncing back from the reflecting surface are called reflected
sound waves. For all practical purposes, the point of incidence and the point
of reflection are the same point on the reflecting surface.
A perpendicular drawn on
the point of incidence is called the normal. The angle which the incident sound
waves makes with the normal is called the angle of incidence, "i".
The angle which the reflected sound waves makes with the normal is called the
angle of reflection, "r".
Let’s look at the two laws of reflection
The following two laws
of reflection of light are applicable to sound waves as well:
- The
incident wave, the normal to the reflecting surface and the reflected wave
at the point of incidence lie in the same plane.
- The
angle of incidence ∠i is equal to the angle of reflection ∠r.
Materials Required:
Protractor table with
two hollow tubes and a reflecting surface, alarm clock
Procedure:
1. Take a sound reflection apparatus
that consists of two hollow cylindrical tubes, a sound reflecting surface and a
protractor.
2. Move tube 1 towards left
at an angle of 200 on the protractor.
3. Now take a alarm clock
and position it at the mouth of tube 1.
4. You can hear sound waves
passing through tube 1.now move tube 2 to catch the sound wave from tube 1. Once
the maximum intensity is obtained through tube 2,fix the tube at that angle.
5. Note the angle of
incident and angle of reflection.
6. Repeat the same above
steps by moving tube 1 and then tube 2 at various angles.
Observations:
Result:
The angle of incidence
is equal to angle of reflection.
Learning Outcomes
Student will understand
the First and Second Laws of Reflection.
First Law of Reflection: The incident wave, the reflected wave, and the normal at the point of incidence lie on the same plane.
Law of Reflection: The angle of incidence is equal to the angle of reflection.
First Law of Reflection: The incident wave, the reflected wave, and the normal at the point of incidence lie on the same plane.
Law of Reflection: The angle of incidence is equal to the angle of reflection.
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