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S/E Physics LABBartlett Archer Shappee:

      Sunday, April 13, 2003

 

The goals of this lab were to show that light is a wave because it follows the two Laws of Reflection, to show that the position of the object, the position of the image and the focal length of a mirror are related by the equation 1/do + 1/di = i/f, to learn the differences between real and virtual images, and to learn how to use parallax to determine the position of a virtual image.  To accomplished this lab we performed a various number of test using a plane mirror, convex, and concave mirrors, light sources, and pencils as objects of reflection.

 

Two Laws of Reflection

  1. The angle of incidence is equal to the angle of reflection.
  2. The incident light ray, the reflected light ray and the normal to the interface all lie in the same plane.

 

A real image is one which is   .  A virtual image is one in which 

Part A:

 

            In order to test the first law of reflection in relation to light we set up an experiment with a plane mirror and a pencil and placed a pencil on one side a normal (non determined to point) and placed another marker on the other side of this normal in the line of site of the first pencil, determined the normal and measured the angels.

 

incidence =

reflection =

 

incidence

 

 

 

reflection

 

            We can conclude with significant evidence, the overlapping bar graph of angles to accept the first law of Reflection in relationship to light.  Also as seen in the diagrams of the expirment it can be seen in the planar representation of the experiment that the incident and reflected waves and the normal to the interface all lie in the same plane.

 

            To measure the focal length of a plane mirror we placed a pencil behind the plane mirror and one in front the mirror, we moved the one in front until the bottom of the pencil lined up with top of the first pencil from all views.

Plane

Mirror

 

Di = distance behind the mirror =

Do = distance in front of the mirror =

1/f = 1/do + 1/di = 1/  + 1/  =

f =    m

 

            The image produced by the pencils is erect.

 

 

 

 

 

Part B:

 

            The focal point of the convexing mirror is behind the mirror since triangle D1 and D2 are similar triangles, generating a virtual image.

To  determine the focal length focal length of a convexing mirror, we shone a narrowed film strip beam of light onto the mounted lens which is projected onto a screen, allowing us to get d2. 

 

d1 = diameter of reflection =

d2 = diameter of mirror =

x = distance between reflection and mirror =

 

 f    = d2

x+f    d1    d2 * (x+f) = d1 * f 

 

 

 

 

Next we placed a rubber stopper and pencil behind and in front of the mirror, moving the pencil behind the mirror until the image seemed to be aligned.

 

di = distance behind the mirror =

do = distance in front of the mirror =

1/f = 1/do + 1/di = 1/  + 1/  =

f =    m

 

Focal length with reflections

 

 

 

Focal length with pencil

 

            To find the magnification [M] of the mirror we found the ratio of the original template size and then compared it to the ratio of distances.

 

Ho (diameter of the pencil behind) =

Hi (diameter of the image of the pencil) =

M = Hi / Ho =

 

Magnification

 

 

Proportin of distance

di / do

 

 

            The image is erect.

 

 

Part C:

 

            To find the focal length of a concave mirror we mounted the mirror and a projection screen, and then added a light source point with a template on it aimed at the mirror. 

 

d0 =

d1 =

1/f = 1/do + 1/di = 1/  + 1/  =

f =    m

 

            Next we found the magnification of the mirror.

 

Ho =

Hi =

M = Hi / Ho =

 

Magnification

 

 

Proportin of distance

di / do

 

            The image is inverted.