Activity

Experiment 12: CD&DVD DIFFRACTION

10/11/2012

The purpose of the experiment is that the grooves on the CD and DVD. And compare to the manufacturer's standard value.

Equipment for the experiment: Laser, CD & DVD, a paper with a small central hole, meter stick.

First, we placed the paper with a hole by two wood. Make sure the laser go through the hole and then place the CD and DVD on the other side. Try your best to make the CD and DVD perpendicular to the laser and measure the distance between CD, DVD and the paper. 

Try to make the all dots show on the paper.

The first one is for CD and the second one is for DVD. Because the distance between the grooves are different and we want to make it easy to measure the two bright dot we place DVD much closer to paper. Then we use pen mark it down. And use rule to measure the distance.

Then, we use the equation from the class which showing below.

The CD grooves distance we got is 1590nm which is closed to 1600nm. And the DVD we got is 743nm. And to explain the equation, because this is the first order maxima, so m=1. Then d=a.We follow the equation sin(theta)=lumda/d theta is angle which the dot is bright. but d=a so we can use this equation to find a. And this is exactly a triangle. So use the geometry to solve for a which we got is 1590nm for CD and 743nm for DVD. So this experiment we got almost correct measurement. And we learn how difference the distance between CD and DVD, because DVD can storage more information, so the distance should be closer so that can storage more. And base on the technology,that's why CD is cheaper than DVD. 

Experiment 11: Measuring a human hair

10/9/2012

In this experiment, we used two different methods to measure the thickness of a hair. Accurately measuring the thickness of a human hair can appear to be a difficult undertaking. However, with the aid of a laser or a a micrometer, we find that obtaining this measurement is not as difficult as we may thought.

First, we using a note card and make a clean hole. Then tape a hair across the hole in the card so that the hair is taut. Clamp the card so that it is parallel to the white board. Mount the laser so that it points perpendicularly toward the wall through the hole in the card. Note the wavelength of the light that the laser emits. Measure the distance from the card to the whiteboard. 

 We try to tape the hair in the middle of the hole.

 We use a cell phone to hold the card so that it cant move.

 We measure the distance from the white board to the laser which is 147.3cm+/-0.1cm

As you can see, it is existing interference on the white board.

Then use a marker to make points. We made the minima points. 

Then we collected all datas and find the d.

Follow the equation, d=lumda*L/Y which d we got is 0.11mm+/-0.03. And we measured by micrometer is 0.08mm+/-0.01mm. It is still existing a big errors. 

In conclusion, we learned how to use the micrometer to measure and the equation y=lumda*l/d is alright. And we find that when the white board go further. The imagine is turning ambiguous, but if we put the white board too close to the laser, it is hard to measure the distance between the minima. 

Experiment 10: Lense

10/4/2012

In this Exploration we observe some other characteristics of a converging lens when the object is placed on one side of the lens and the real, inverted image is placed on the other side of the lens.Also, we develop a mathematical relationship between the object distance and the image distance.

The equipment we need: lamp, converging lens, lens holder, paper, meter and meter stick.

First, we measured the focal length under the sun. When the image on the ground is a bright dot, then measure the distance from the dot to the middle of lens by ruler. f=4.5+/-0.2cm

Then we set up the equipment.Measure the height of the object.

And make the object distance to 1.5f, 2f, 3f, 4f, 5f. The place a paper on the other side so that can get a clear image. Then measure the image height. And the object distance and image distance.

Of course, we also reserve the lens in the same object distance. But we got the same image distance. And we also cover the top half of the lens by a paper. It is dimmer as you can see.

Then collect all data and make a form.

Change the object distance to 0.5f There is no image on the paper but we look through the lens at the object to view the image. The image is virtual and repeating.

Set up a graph for those datas. 

The y-axis is inverse image distance and the x-axis is negative inverse object distance.The slope is 1.0233 and the y-intercept is 0.218

The y-intercept should be the image distance when x close to zero which means object distance is infinity. The inverse of y-intercept is the focal length of lens which is 4.587. It is closer to what we measured.(4.5+/-0.2) 1/di=1/do(1.0233)+0.2180

Experiment 9: Concave and Convex Mirrors

9/25/2012

The purpose of this experiment is discovering the image formed by both a convex and concave mirror.

For this experiment, we need a convex mirror, concave mirror, object(marker), ruler and worksheets.

First, we measure the height of the marker which is 11.95+/-0.05cm.

Then we place an object in front of a convex mirror. 

The image appears smaller than the object. The image is upright. The image is in front of object and seem further in the mirror. When we move the object closer to the mirror. The image is changing larger till it is as same size as the object.

When we move the object further from the mirror than it was in step 1, we find that the image is changing smaller.

 Then we measure the distance between object and mirror which is 50.00+/-0.1cm, and the height of image is 3.9+/-0.1cm. Then we can calculate the magnification is hi/h0=0.326+/-0.01, then due to the relationship between distance and height, we can find the distance between image and mirror is 16.32+/-0.52 cm.

In part B, we place the marker in front of a concave mirror.

The image appears bigger than the size of object. The image is upright. The image is in front of the object and it is closer in mirror. When move the object until it is close to the mirror, the image is changing smaller till it is as same as the size of the object. And it is upright. When we move the object much further from the mirror than it was in step1, we find that the image is changing bigger first then become smaller and smaller and from upright to inverted.

We measure the distance between object and mirror is 89.05+/-0.05cm. And the height of image is 24+/-0.1cm. Then we can calculate the magnification is 2+/-0.02cm. Then we also can calculate the distance between image and mirror is 178.85+/-1.6cm.

Expriment 7: Introduction to Reflection and Refraction

9/22/2012

The purpose of the experiment is measure the incident angle and the refractive angle and find the relationship between them.

Equipment: Light box, semicircular plastic or glass prism, circular protractor, pasco optical kit or hardtl disk.

The angle of incidence for the light ray at the flat surface is theta1, the angle of refraction at the flat surface is theta2. When light ray leaves the plastic piece at the curved edge and goes in to the air, it has no refraction between the cured edge and air; just a straight light ray passing through it. This experiment is from lower density to higher density.

Set up the equipment shown as above and begin measure it. Let make theta1 begin from 5 degree to 70 degree.

Then we can collect the measurement and make a graph which is linear. We found that the slope is 0.6676. n1*sin(theta1)=n2*sin(theta2) We know that n1 is the index of air which is 1. so the 1/n2=sin(theta2)/sin(theta1)=0.667 then we can calculate the n2 which is index of glass is 1.49.

Then we change the the glass direction. And set up the equipment shown below.

 When the light ray through the first curved surface of the semicircular prism, the light ray doesn't have any changes. Because the angle of incidence is ever zero. When it strikes the flat surface, there is refractive angle. This experiment is from greater density to one of lower density.
Then we begin measure the angle of refraction and make a graph.

From the graph, we know we can complete all 10 trails, because when the incident angle is over 45degree. There has no refraction.

The slope of the graph is 1.46. n1*sin(theta1)=n2*sin(theta2) n2 is the index of air which is 1. So n1=sin(theta2)/sin(theta1) n1 is the index of glass which is 1.46.
Summary: Ok, now we have two slope of the graph which one of them is 0.667 and other is 1.46. Is it incorrect??? No for sure. Because they are different cases, one is from lower density to higher density; other is opposite. Although we used the same equation n1*sin(theta1)=n2*sin(theta2), but because the situation is different, so the n1, n2 will be changed. n2 is the index of glass from part one; n1 is the index of glass from part two. So the result we got 0.667 is closed to 1/1.46. Of course, we have some errors when we measure the refractive angle because the light is so wide not just like a small line.