Measuring a human hair

Today we measured the thickness of a human hair by diffraction of light.
For a double slit diffraction of a light beam, light and dark interference spots are created on a surface some distance L from the slots.
If the slots are separated by a distance d,  the distance from the center bright spot and bright spot #m is y = λL*m/d
We treat the human hair as the separation between openings and if we shine a laser at the hair, we get a corresponding diffraction pattern on a distant surface.

We placed a whiteboard 1 meter away from the hair, to simplify calculations. our λ was 680nm for a red laser. We measured the distance between the center and the 4th bright spot and got y=4.8 cm
Rearranging and plugging in we got d = 680e-9*1m*4/.048 = 5.67e-5m = 56.7 μm

My hair is on the very lower border of human hair thickness according to google. Makes you think I have alopecia or something haha

Lenses Lab

In this lab, we looked at the behavior of light through a magnifying glass which is a double convex lens.
We used a light box which illuminated a pattern on a piece of paper, and placed the magnifying glass at specific distances away from the light box, and had a blank sheet on which to project the image.

Before we could do anything, however, we needed to measure the focal length of our lens. To do this, we went outside and focused the light from the sun onto the ground until the light entering the lens was focused at a single point. The focal length was simply the height above the ground.
The focal length of our magnifying glass was found to be  f = 14 cm +/- 0.5 cm

After that, we placed the light box at various distances (object distance) from the lens, and found the image distance (where the projection on the sheet was most clear) and measured the image height on the sheet. The object height is constant and is simply the height of the printed pattern on the paper on the light source.

Object distance (cm)	Image Distance (cm)	Image Height (cm)	Object height (cm)	Magnification
5*f = 70	22.5	1	3 cm	1/3
4*f = 56	24	1.5		1/2
3*f = 42	28	2		2/3
2*f = 28	43	4.8		1.6
1.5*f = 21	85	12.5		4.2

We then tried to get an image when the light box was only 0.5*f away from the lens. We were unable to get a image to show up on the sheet at any distance. However, we are able to see a very clear virtual image by looking through the lens from any point.

Concave and convex mirrors

In this lab, we looked at reflected images in concave and convex mirrors.

In a convex mirror, (curved outward) objects appear smaller than normal and warped. This stays the same regardless of where the object is in relation to the mirror.

In a concave mirror, however, interesting things happen. Close to the mirror, objects look much bigger than normal. This happens at distances closer than the focal length of the mirror. When the object is moved farther away, the image inverts and appears to shrink.

After observing the concave and convex mirrors, we constructed ray diagrams and calculated magnification.

From the ray diagrams, we measured the object and the image height in order to calculate magnification, which is M = obj height / img height.
For the convex mirror, the theoretical magnification was 1.25/.25 = 5
For the concave mirror, it was negative 5 because the image is upside-down. (the rays don't intersect properly because the focal point isn't placed quite right)