assignment-3 (MaxwellNeedle)..pptx

Maxwell Needle Experiment physics honours

1. MAXWELL’S NEEDLE

2. AIM:- To determine the modulus of rigidity of a wire of some material using maxwell’s needle.

3. APPARATUS REQUIRED:- Maxwell Needle Screw Gauge Meter Scale Weighing Machine Stop Watch. Knitting needle as a reference Telescope as a point of viewing.

4. THEORY:- Modulus of Rigidity:- Modulus of Rigidity is basically the ratio of shear stress to the displacement per unit sample length (shear strain). More specifically, modulus of rigidity (Shear Modulus) is the coefficient of elasticity for a shearing force. Modulus of Rigidity = Shear stress/Shear strain.

5. Maxwell’s needle is basically an empty hollow brass tube tied to a string.The free end of string is attached to the fixed support. In addition to this, there is a mirror present on the maxwell’ s needle which helps in recording time period of oscillations. We also have 2 solid cylinders and 2 hollow cylinders. Diameters of all 4 cylinders are identical and slightly less compared to the long brass rod. The length of small 4 cylinders is L/4 ( where L is the length of long cylinder.) In the Maxwell’s needle experiment, 2 major configurations are used :- Configuration 1 :-

6. Configuration 2 :- For both these configurations time period is to be noted as shown in the procedure.

7. Formulae Used; 1- Here, L = length of Maxwell Needle l = length of wire. M(s) = Mass of solid cylinder. M(h) = Mass of hollow cylinder. T1 = Time period in configuration-1 T2 = Time period in configuration -2 r = radius of wire

8. PROCEDURE:- Measure the length of wire using meter scale through which the maxwell needle is hanged . This will give you value of ‘l’. Measure the length of maxwell needle wing meter scale . This will give you value of ‘L’. Measure the mass of both solid cylinders using balance and do its half, this will give you value of M(s). Measure the mass of both the hollow cylinders and do its half to get M(h). Find out the least count of screw gauge and zero error in it. Using screw gauge , measure the diameter of wire.(Observation table.) Find out least count of stopwatch. Now make the first configuration and oscillate it in horizontal plane about vertical axis . Note the time for 20 oscillations using the knitting needle as reference and using telescope for viewing. [Note- the first oscillation is to be taken as 0 th oscillation.] Repeat the same thing for configuration-2. Note the values , fill the observation table , put the values in the required formula and hence calculate the modulus of rigidity.

9. Calculating time period for oscillations as instructed in the following video…..

10. OBSERVATIONS:- Calculating diameter of wire using screw gauge. Mean diameter = 0.0475 cm Mean radius = 0.02375 cm

11. Calculating time period for configuration 1 and 2 :- Mass of solid cylinder = 250 grams. Mass of hollow cylinder = 70 grams. Length of wire = 54.5 cm. Length of Maxwell Needle = 40 cm.

12. CALCULATIONS:- Putting values We get, This Photo by Unknown Author is licensed under CC BY-ND

13. RESULT:- Hence, Modulus of Rigidity of the given wire comes out to be 0.830 × 10 ^ 11 N/m^2. On seeing the table we find , The value of η corresponds to that of iron wrought cast. Therefore, we conclude material is Iron wrought.

14. PRECAUTIONS:- 1-There should be kink in the wire. 2-The maxwell needle should remain horizontal in the same plane . 3-the amplitude of oscillation should be small so that wire is not twisted beyond elastic limit. 4-To avoid backless error, circular scale of screw gauge should be moved in only one direction. ****