Two glass tubes of 3 ft. in length and 2 inches in diameter.
Vertical reflector (say a polished wooden drawing board).
Sounding body (Galton's whistle or clock).
Procedure: As done in a real labArrange two glass tubes;
AB and CD each horizontally at some angle in front of a vertical reflector R1R2 (a polished wooden drawing board).
At the mouth A, of the tube AB, place a sounding body (a tuning fork or a clock).
Adjust the inclination of the tube CD with respect to the reflector R1R2 so that the sound is distinctly and loudly heard when the ear is placed at D.
Mark the portion of tube AB and CD.Draw a dotted line from the centre of diameter of tube AB and CD and extend up to reflector board.
Draw a normal
.Measure the angle between the sound waves coming from the tube AB and the normal (ie. the angle of incidence of sound waves)∠AON called angle of incidence, ∠i.
Then measure the angle of reflection, ie., angle between normal and the central line drawn from the tube CD, when the sound is distinctly and loudly audible.
This is the angle of reflection of sound wave, ∠r, ie. ∠DON
As done using the simulator--
Select the ‘Show Protractor’ button to show the protractor.
The protractor can be rotated by clicking over the two way arrow mark shown on the protractor and dragging it.
The speaker icon depicts that the simulation involves sound which ensure that you must use an audio device (head phone or speakers).
Now move the lower end of Tube 1 to the left at an angle of 20o on the protractor.Then position the tuning fork at the mouth of Tube 1.
This can be done by dragging the tuning fork with the mouse
.You can hear the sound waves passing through Tube 1.Now move the lower end of Tube 2 towards the right to catch the sound waves passing through Tube 1.
Once you get the maximum sound through Tube 2, fix the tube at that angle.Note down the Angle of Incidence and Angle of Reflection.
You will notice that both are the same ie., 20o
.Repeat the same by moving Tube 1 to the left at angles 40o, 60o and 80o and note down the angles at which the maximum sound is obtained through Tube 2.
Note:The ‘Hide Tubes’ button can be used to hide the tubes so that you can take accurate readings.The ‘Hide Waves’ button can be used to hide the waves.
Observations:The tubes carrying sound waves, the normal to the vertical reflector and the reflected wave are in the same plane.
Measure the angle of incidence and angle of reflection and record the observations in a table as given below:
Sl. No Angle of incidence ∠i = ∠AON Angle of reflection ∠r = ∠DON
From the above observations, we can conclude that angle of incidence ∠i = angle of reflection ∠r.Inference: Since the tubes are normal to the vertical reflector, and the reflected wave lie on one and the same plane, the First Law is verified.The angles of incidence and the angle of reflection of sound are found to be equal, which verifies the Second Law.
Precautions:The inner surface of the metallic tube should be highly polished.
Metal plate should be highly polished.
The tuning fork should be close to the tube, but it should not touch the tube.
There should be complete silence in the laboratory so that sound from other sources does not interfere.
The ends of metallic tubes should project out at least 1cm from the edge of the table top.