Physics lab 2021

physics lab on medels experiment

1. PH112 (PHYSICS-II) LAB MO-2021

2. To determine the frequency of electrically maintained tuning fork by Melde’s experiment OBJECTIVE OF THE EXPERIMENT

3. Riya Biswas (LEADER) Aayushi Sinha Akanksha Kumari Shristi Singh Mousumi Pradhan Rohan Sinha Saprativa Sarkar Tushar Kumar Mehul Verma 1. 2. 3. 4. 5 . 6 . 7 . 8 . 9 . Team Members

4. THEORY Standing waves and Normal mode of Vibration Melde’s experiment

5. Standing waves and Normal mode of Vibration We know =>   =wave length =frequency =velocity of wave   Again speed of wave in stretched string   =velocity of wave =tension in string =mass per unit length   The points of the medium which have no displacements called  nodes.   There are some points which vibrate with maximum amplitude called  antinodes.

6. The distance between two consecutive nodes is λ/2. Fundamental Frequency Or First harmonic frequency We know   and     hence,  

7. Second Harmonic / First Overtone     Third Harmonic / Second Overtone     NOTE : In general ( overtone / harmonic is    

8. = frequence of string = frequency of tuning fork = Number of Loops produced in string = length of thread T = tension produced in the string = (Mass of sting + Mass of suspended part)*g = ( M+m )*g =mass per unit length   Here we denote -

9. Melde’s Experiment Used to demonstrate stationary wave in a stretched string using a large electrically oscillating tuning fork Two Modes of Vibration Transverse Mode Longitudinal Mode

10. Transverse Mode In transverse Mode the string completes one vibration when tuning fork completes one  

11. Longitudinal Mode In Longitudinal Mode the string completes half of its vibration when the tuning fork completes one vibration.  

12. NOTE : In Transverse mode of vibration, vibration of prongs are in the direction perpendicular to the length of the string. In Longitudinal Mode of vibration, vibration of prongs are in the direction parallel to the length of the string In transverse drive mode the string follows the motion of the tuning fork, up and down, once up and once down per cycle of tuning fork vibration. However, one cycle of up and down vibration for transverse waves on the string is two cycles of string tension increase and decrease.

13.   The tension is maximum both at the loops’ maximum up position and again at maximum down position. Therefore, in longitudinal drive mode, since the string tension increases and decreases once per tuning fork vibration, it takes one tuning fork vibration to move the string loop to maximum up position and one to move it to maximum down position. This is two tuning fork vibrations for one up and down string vibration, so the tuning fork frequency is half the string frequency.  

14. In both case frequency of Tuning fork is constant This is called MELDE’S LAW In constant frequency if tension increases then number of loops will decrease. In constant frequency if tension decreases then number of loops will increase. If Melde’s experiment is performed for two different tension in string , say and for which stationary waves are obtained with loops in string we can use       Hence,

15. 1. Find the mass of the scale pan M' and arrange the apparatus as shown in figure. 2. Excite the tuning fork by switching on the power supply (advisable to use voltage more than 6V) 3. Adjust the position of the pulley in line with the tuning fork. 4. Change the load in the pan attached to the end of the string. 5. Adjust the applied voltage so that vibrations and well defined loops are obtained. PROCEDURE

16. 6. The tension in the string increases by adding weights in the pan slowly and gradually. For finer adjustment, add milligram weight so that nodes are reduced to points at the edges. 7. Count the number of loop and the length of each loop. For example, if 4 loops formed in the middle part of the string If 'L’ is the distance in which 4 loops are formed, then distance between two consecutive nodes is L/4. 8. Note down the weight placed in the pan and calculate the tension T . 9. Tension, T = ( wts on the pan + wt. of pan) g. 10. Repeat the experiment for longitudinal and transverse mode of vibrations. 11. Measure one meter length of the thread and find its mass to find the value of mass produced per unit length ( ms ).

17. S.No Weight( Mgm ) No. of loops (P) Length of thread(cm) Length of each loop Tension( M+m )gm Frequency 1 10gm 5 148.5cm 29.7cm 25g 68.8Hz 2 15gm 5 148.5cm 29.7cm 30g 74.8Hz 3 20gm 4 148.5cm 37.1cm 35g 81.4Hz 4 23gm 4 148.5cm 37.1cm 38g 84.2Hz 5 25gm 4 148.5cm 37.1cm 40g 86.4Hz 6 30gm 4 148.5cm 37.1cm 45g 98.4Hz 7 33gm 7 145.8cm 20.8cm 48g 94.0Hz 8 35gm 7 145.8cm 20.8cm 50g 137.9Hz 9 40gm 3 145.8cm 48.6cm 55g 61.9Hz 10 42gm 3 145.8cm 48.6cm 57g 63Hz 11 45gm 3 145.8cm 48.6cm 60g 64.6Hz Table-1: Frequency of transverse mode arrangement.

18. Graph for Table 1 Mean frequency= 70.04 Hz

19. T able-2: Frequency of longitudinal mode of arrangement SL NO. WEIGHT M (gm) NO. OF LOOPS (P) LENGTH OF THREAD (cm) LENGTH OF EACH LOOP (cm) TENSION T (M+m) gm FREQUENCY(Hz) 1 7 gm 2 8 cm 3.5 cm 10 gm 60 Hz 2 12 gm 2 8 cm 3.5 cm 15 gm 60 Hz 3 15 gm 3 8 cm 3.2 cm 18 gm 60 Hz 4 18 gm 3 8 cm 3.2 cm 21 gm 60 Hz 5 22 gm 3 8 cm 3.2 cm 25 gm 60 Hz 6 24 gm 3 8 cm 3.2 cm 27 gm 60 Hz

20. Voltage= 8v Mass of pan(m) =3 gm Mean frequency= 60 Hz  

21. A string undergoing transverse vibration illustrates many common to all vibrating acoustic systems like the vibrations of violin or guitar. The change in frequency produced when the tension is increased in the string-similar to change in pitch when a guitar string is tuned-can be measured. Tuning of instruments like guitar The vocal organs of human beings form a continuous hallow tube with different cross sectional areas acting as a filter to regulate the output sound. The interaction between air flow and the vocal cords periodically opens and closes the glottis, resulting in a harmonic sound wave, which in fact is the source of the sound. Human speech analysis Applications The standing waves formation in strings(Melde’s experiment)can demonstrate that the formation of waves in air column is the result of reflections of the vibrating air inside the instrument, and thus sound is produced. These patterns are complex and usually waves of several frequencies are present. Standing waves in air column, soprano saxophone, etc .

22. 1. The thread should be uniform and inextensible. 2. Friction in pulley should be small. Otherwise it causes the tension to be less than the actual applied tension. 3. The loops in central part of thread should be counted for measurement. The nodes at pulley and tip of prong should be neglected as they have some motion. 4. The longitudinal and transverse arrangements should be correct otherwise the length measured will be wrong . Precautions :

23. Contribution Of Team Members Riya Biswas Leader of the team Application slide-prepared and presented Editing the ppt. Aayushi Sinha Procedure slide- prepared and presented Shristi Singh Precautions slide –prepared and presented

24. Contribution Of Team Members Rohan Sinha Transverse wave Graph slide- prepared . Editing of PPT Tushar Kumar Transverse wave Graph slide- prepared and presented. Editing of PPT Mehul Verma Theory slides-prepared and presented.

25. Contribution Of Team Members Saprativa Sarkar Theory slides-prepared and presented Mousumi Pradhan Longitudinal wave Observation table- prepared(performed in virtual lab) Longitudinal wave slides- presented Akanksha Kumari Longitudinal wave Graph slide- prepared

26. THANK YOU