Experiment 11: CD Diffraction

Purpose: to figure out the distance beween the grooves on a CD using diffraction methods.

Equipment:

• Laser
• CD
• Meter stick(2)
• Clamps
• White board

Experiment:

The laser was arranged to shine a beam through the hole in a screen and strike the compact disk, a distance of ~0.5 meters.

The beam was perpendicularly striking the disk at a place where the grooves were tangentially vertical with the first order maxima.

Once the diffraction pattern appeared, the distance between the maxima was measured using the a smaller ruler at a known fixed distance fromt he CD.


Conclusion:

Based on the calculations made in this experiment, the distance of the grooves are 1535nm apart, which is a close answer to 1600nm with a 4.06% error

Experiment 10: Measuring human hair

Purpose: to measure the thickness of human hair using a laser and a micrometer in order to compare the two different methods of measureming.

Equipment:

• Notecard
• Human hair
• Tape
• Lazer
• Meter stick

Experiment:

A hole was punched into a notecard, for which a human hair from a classmate was then taped across the diameter of the small perfuration.



In a darkened classroom, the red lazer was turned on, turning the thickness of the hair into a slit to cause a diffraction pattern as observed bellow.

The distance from which the hair was positioned was measured to be ~1meter as displayed bellow

The diffraction pattern was then physically drawn onto the white board suface for further measurements with the classroom light on. This allowed us to visualize the distance between minima as shown in the next image.

Conclusion: 

It was determined that the experimental method of using a lazer to measure human hair was within an acceptable range of value after calculating the uncertainty of its diameter based on the average diameter for black hair.

Experiment 9: Lenses

Purpose: To observe some of the 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.

Equipment:

• Convergering lens
• Light box with outline image
• Meter stick
• 12 inch ruler
• Lens holder
• White board



Experiment:

Light Box with outline image to be projected

Physical Set up of the experiment

In the experiment we determined the focal length of the lens by using a simple visual analysis and measurement.

A focal point distance from the surface to lens was measured by holding the lens horizontally above a lamp until the light was maximized using a 12 inch ruler.

f = 5.2 ±0.5 c.m


The lens was then clamped onto a holder, and set at a distance of 1.5f, 2f, 3f, 4f, and 5f and fixed at an object height for the experiment.


This resulted in different image distance and image heights.


Table 1: Measured Data

The uncertainty was calculated using the max/min values for Magnification calcuation. And bellow is a sample calculation.  

At an object distance of 0.5f, the image was completely blurred and it bacame virtual, as shown in the image bellow

As shown in the picture above, it is completely viewable inside the lens itself.


Conclusion:

In plotting the inverse image distance vs. negative inverse object distance yileded a linear relationship confirming a correct initial focal length.

Eqs.        1/q = -m/p +b
                1/q = -1/p +1/f