Lab Report: C S G G M E

 

 

 National University University of Sciences and Technology (NUST) SMME

LAB REPORT Report # 2

Course : Applied Physics Section : ME-10 (A) Group : B-3 Group Members:  Ali Asad Altaf Ahmad Ali Raza

Experiment Info:  Experiment Date: Sep 25, 2018  Topic: Ripple Tank Submitted to: Mam Bushra Yasin

 

  INTRODUCTION: 

Ripple tank is an apparatus to study the processes like reflection, refraction, diffraction etc. It consists of a tank, wave generator and a light source. source. Waves are generated by wave generator generator whose frequency and amplitude can be controlled. A light source helps to projects the waves onto a screen. It has two parts: •

Screen display: consists of a reflector and projection screen

•

Ripple tank display: It consists of a the body of ripple tank, light source and and its stand

 

REFLECTION   Abstract: The purpose of this experiment is to show the law of reflection. This can be proved by using a vibrator to generate waves which will then collide with a relatively denser obstacle and waves reflect by the denser part. The angle of incidence and reflection will be measured in plan surface and if equal, it shows that the law of reflection is true. Three types of barriers will be used plane barriers, convex barriers and concave barriers. In the case of convex or concave barriers, the distance between the point where the reflected waves interfere destructively and the middle of the barrier will be one half of the distance of the two normal drawn from 2 points, symmetrically placed, at a distance away from the middle of the barrier.

Theory: Reflection encompasses the bouncing back of a wave front when it strikes another medium(denser). The direction of a wave front is shown by a ray. Ray is basically a line perpendicular to a wave front and it used to show the wave front. This property of waves is explained by the law of reflection which emphasizes that the angle of incidence and reflection must be same in all cases. The angle of incidence is the angle between the incident ray and the normal to surface. The angle of reflection is the angle between the reflected ray and the normal to the surface.

REFLECTION BY A PLANE SURFACE: Procedure:

 

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The ripple tank is set up and level by balancing screws on the stand and the frequency generator. Add the sufficient amount amount of water and barrier is placed at a certain angle to the generator generator in the water . Turn on the generator and light. Set the light in strobe mode. Adjust the specific frequency of the ripple generator and strobe light so that stationary image of waves obtained. The frequency is generally set up at 20 Hz. The amplitude of generator is set up slightly less than half of its max value. Place a sheet below the glass plate of the ripple tank. Using a ruler, draw lines parallel to the wave wave fronts obtained on the paper. Draw two lines each for incident and reflected waves respectively. Mark the boundary of the barrier to show the straight surface of the long barrier.

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Make clear, accurate and straight lines using the ruler.

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Draw a line perpendicular to the line of the incident wave front. Join this line to the straight surface of the long barrier. Draw a normal at the surface of the long barrier.

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•

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Draw a line perpendicular to the reflected wave front at the point where a normal was previously drawn. Using a protractor, measure the angle of incidence and angle of reflection respectively (with respect to the normal). Percentage Error formula

is

then

calculated

             ))  ( 

%Error=

           

∗100 

using the

 

Data Analysis:

%Error = (

Angle of incidence

37.5 

Angle of reflection

39 

37.5 −39 37.5

)*100 = - 4.0 %

.Conclusion: The angle of incidence is not equal e qual to angle of reflection, thus there is a slightly error of --4.0%. 4.0%. The -ve sign shows that the obtained value is less than intended value.

REFLECTION BY A PLANE SURFACE IMAGE:

 

REFLECTION USING A CONVEX BARRIER Procedure: •

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Add water to the tray of ripple tank and place a curved convex barrier in front of the wave generator Adjust the frequency of strobe light so that waves become clearly visible Place a sheet under the tray as a screen and trace the curved barrier the produced wave fronts as well as the reflected ones. Mark the spot at which the reflected waves appear to converge. Draw tangent lines to the reflected curved waves to show their direction of travel. When the normal at the points of tangency drawn they should pass through the marked focal point. Measure the distance, f, to the focal f ocal point from the middle of the barrier. Draw tangents to the surface of barrier and construct their normal. Extend the normal so that they meet each other at a point. This is the radius of curvature of the convex barrier. Measure the radius, R.

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Multiply the f with 2 it gives the radius R.

•

Calculate the percentage error by, %error =

| Measured Measured  R−Expected R−Expected  R| Expected R Expected 

 * 100

Date Analysis:

Focal Length

6 cm

Radius of Curvature, R. Expected R

12.2 cm 12 cm

12.2−12 

%error =(

12

)*100 = 1.67 %

CONCLUSION: The error in the experiment e xperiment comes to 1.67 % which is an acceptable error, therefore it can be concluded that the focal length is approximately equal to one-half of the radius of the curvature. The error can be accounted by the difficulty to find the exact point of focus due to

 

the slight disturbance of the water at the point, furthermore the inability to sketch the exact curve of the barrier, thus resulting in i n errors in the radius of curvature measured.

REFLECTION USING A CONVEX BARRIER IMAGE: 

 

REFRACTION OF WAVES Abstract The refraction is done in a ripple tank with the help of refractors like: 1. Trapezoidal Refractor  

2. Convex Refractor  

3. Concave Refractor  

REFRACTION:

“Refraction is the bending of waves on passing from one medium to another.” In refraction the angle of refraction depends upon the ratio of refractive indices of two media of travel.

Theory: Refraction show the change in direction, speed and wavelength of waves on entering from one medium to another. Frequency does not change by the phenomena refraction. The ray which iiss refracted may be bent towards the normal or away the normal. Angle of refraction depends upon the refractive index of the medium.

REFRACTION FROM A TRAPEZOIDAL REFRACTOR: PROCEDURE:

 

  Adjust the horizontal level of the ripple tank. Add water water in the tank with the help of dropper. Place a trapezoidal refractor in the tank with its straight edge parallel to plane wave dipper. It should be carefully noticed that the refractor fully immersed in water. •

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Set the light to ‘STROBE’. Turn on the plane wave generator with its frequency equal to 15 Hz. Note the pattern of the plane waves. On the sheet below, trace the pattern of the plane waves with the help hel p of ruler. Also trace the pattern of the refracted waves on the outline of the refractor. Repeat the same procedure by reversing the sides with the triangular part on top.

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Turn off the device.

•

Calculate the percentage error by, %error = (

Measured  n−Expected n−Expected  n | |Measured   Expected n Expected 

) ∗100 

DATA ANALYSIS: •

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•

Draw a line perpendicular to incident waves with an arrow head pointing towards the refractor. This line is the incident line. Similarly, at the outline of the refractor where the incident wave bends, draw another line perpendicular to the refracted wave. This line is the refracted line. Draw a normal to the refractor’s refracting edge and measure the angles made by the incident line and refracted line with the normal. They are called as angle of incidence and angle of refraction respectively.

TRAPEZOID UP:

Angle of incidence