Tuesday, May 3, 2016

49th Annual Summer School Day 7:(02-05-2016) Physics Olympiad Experiments

On 2nd May 2, 2016 in the Summer School of Science we had the privilege to try out the experiments on various aspects of physics prescribed by the International Olympiad for Science under the guidance of professors like Sreedhar Swamy Sir, Kamala Madam and many others.
The list of the experiments that we tried out included:
1. The calculation of Surface Tension and Viscosity of Water.
2. The calculation of Acceleration due to Gravity
3. Diffraction
1. Calculation of surface tension and viscosity of   water:
Aim: To use diffraction of a laser on the water surface to determine surface tension.
In this experiment we use the diffraction pattern emitted by the vibrating water surface to calculate the surface tension of water.
Firstly we determine theta by using trigonometry i.e. we move the light sensor to different markings and then we note down X and Y component then plot a graph and find the slope which is theta.

Calculation of SurfaceTension                                                                       
For calculating the surface tension we use the sound emitting device to produce desired and controlled vibrations in the water surface. Then we obtain a series of diffracted laser points on the light detector then we need to measure the distance between the 2nd order points, then we repeat the same from a frequency of 60 to 180 Hz with an interval of 10 Hz and then plot a graph of f v/s x1. We then calculate slope1. Then we plot another graph of f2 v/s  x13. Then we calculate slope2. Must calculate surface tension using   the given formula.
 Calculation of Viscosity:

For calculating the viscosity of water we must first set the frequency of the sound to 100Hz. We must then set the vibrator marker at 8cm. We must adjust the light sensors using vernier calipers to the 1st order. We must adjust the amplitude such that the lux meter shows a reading of 100 and then note down the Vrms. Then we find out the natural log of Vrms. We must plot a Vrms v/s S and calculate slope3. Then we must calculate Delta and Viscosity.
2. Calculation of time period of a simple pendulum 
 First we need to suspend a metallic bob from a support with its length as 100cm. Then we need to take number of oscillations per minute. After taking down the oscillations we must find out the frequency of the pendulum. Then repeat the same for lengths of 50 and 25cm. Since time period is the reciprocal of frequency
3. Diffraction
A  Brief Introduction about Diffraction:
The bending of waves around the obstacles.  

Diffraction takes place with sound waves, with electromagnetic radiation, such as light, x-rays, and gamma rays and with small moving particles such as atoms, neutrons, and electrons, which show wave like properties.

In light diffraction is the slight bending of light as it passes around the edge of the object. The amount of bending depends on the relative size of the wavelength of light to the size of opening. If the opening is much larger than the light’s wavelength, the bending will be almost unnoticeable.
Applications of diffraction

The effects of diffraction are often seen in everyday life. The most striking examples of diffraction are those that involve light; for example, the closely spaced tracks on CD or DVD acts as a diffraction grating to form the familiar rainbow pattern seen when looking at the disk. The principle can be extended to engineering a grating with a structure such that it will produce any diffraction pattern desired; the hologram on a credit card is also one of the examples.

Today in the lab we studied about LASER DIFFRACTION ANALYSIS also known as LASER SPECTROSCOPY, … this is a technology that utilizes diffraction patterns of  a laser beam passed through any object ranging from nanometers to millimeters in size, to quickly measure geometrical dimensions of a particle .

The apparatus required for this experiment is:  a red laser light which is attached to a wooden platform.  Then we need a lens where the sample is attached (here we studied the structure of spring – or the helical structure).  Then we need 2 reflectors, a black surface which receives the laser light after reflection, and a particular X shape is formed on the black surface.  Then we require a sample holder, a wooden platform, a direct current source, clips, a mirror and a plane white sheet
Procedure or the process of the LASER BEAM ANALYSIS
First we switch on the direct current source from where the laser will get power, the laser light is lit up. We were asked to make the reflected ray to go back to the laser i.e. we will have 2 points of the laser on the white paper which will be clipped on the black surface. So to make the rays meet we will have to adjust the black screen, or even sometime the laser. If the apparatus is correct we get an X shaped pattern, and if we observe keenly we get to see small spring shaped structures on the white paper. Then we had to mark the distance between the two consecutive springs using a pen pencil, we were also asked to mark the center of the laser beam and the small area around it. Then Y.C.Kamala madam took us through a little bit of trigonometry. 
i.e. sin theta = opposite side /hypotenuse,  
cos theta   = adjacent side/hypotenuse,  
tan theta  = perpendicular/base.  

Based on this basic formula of trigonometry the whole experiment was dependent. So we were asked to measure 2x distance (i.e. the distance between the center point, the upper and the lower widths this would give us 2x), my group took 7 measurements. Then we were asked to construct an order v/s width graph. The slope formula is: measurement on y axis * 2/ measurement of x axis, my team got the value as 2.35.  Then madam told us to measure the thickness of the spring using the formula 2*  (value 635*10-9) * 277/ slope value. As it’s in m form we have to convert it into mm form.  So the denominator is like this slope * 10-2.  Our team got the value as 0.1496* 10– 3m. Then after finding the thickness we have to find the angle in the curve of the spring.  So to find it we have the formula tan theta.  Tan theta = perpendicular / base.  Our team got the answer as 22.29 degrees. So there the experiment ends. In this experiment lot of mathematics, physics and trigonometry is used. 

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