Light and Spectra

In this lab we placed a diffraction grating before a charged gas in order to locate the peak wavelengths that are produced.

The view of charged Hydrogen Gas from a diffraction grating

The view of charged Mercury Gas from a diffraction grating

Relativity of Length

In this thought experiement we used a simulation to explore the concept of length contraction as viewed from various frames of reference when objects are traveling at relativistic speeds.

Question 1: Round-trip time interval, as measured on the light clock
Imagine riding on the left end of the light clock. A pulse of light departs the left end, travels to the right end, reflects, and returns to the left end of the light clock. Does your measurement of this round-trip time interval depend on whether the light clock is moving or stationary relative to the earth?

A. Yes, the measurement depends on ones frame of reference

Question 2: Round-trip time interval, as measured on the earthWill the round-trip time interval for the light pulse as measured on the earth be longer, shorter, or the same as the time interval measured on the light clock?

A. The round-trip interval as seen by all observers other than those sharing the same frame of reference as being on the light clock would count a larger time interval due to the effects of time dilation.

Question 3: Why does the moving light clock shrink?You have probably noticed that the length of the moving light clock is smaller than the length of the stationary light clock. Could the round-trip time interval as measured on the earth be equal to the product of the Lorentz factor and the proper time interval if the moving light clock were the same size as the stationary light clock?

Relativity of Time

This thought process explores the idea of time dilation for objects at speeds approaching the speed of light using a simulation.

Question 1: Distance traveled by the light pulseHow does the distance traveled by the light pulse on the moving light clock compare to the distance traveled by the light pulse on the stationary light clock?

A. The light pulse on the moving light clock covers a longer distance than the stationary clock.

Question 2: Time interval required for light pulse travel, as measured on the earthGiven that the speed of the light pulse is independent of the speed of the light clock, how does the time interval for the light pulse to travel to the top mirror and back on the moving light clock compare to on the stationary light clock?

A. The stationary completes a rountrip from source to mirror and back in less time than that of the mobile light clock

Question 3: Time interval required for light pulse travel, as measured on the light clockImagine yourself riding on the light clock. In your frame of reference, does the light pulse travel a larger distance when the clock is moving, and hence require a larger time interval to complete a single round trip?
A. In my frame reference, I would feel as if I had completed the roundtrip in the same amount of time as I would be traveling at the speed of light which is the same regardless of ones frame of reference.

Measuring a human hair

In this lab, we determined the width of a human hair by utilizing the properties of diffraction from a light source from two slit.  Interference between the light propograting from two source points will result in areas of maximum and minimum intensities.

The Setup:

A notecard has a hole punched through it.  A human hair is attached over the hole vertically and splits the single hole into two.  The width of the hair, 'd', is the width between the newly created dual source point.  A laser will be focused on the hair and will be split by the hair.  The laser will now propogate from two source points and interfere with itself.



Here, we are observing and marking diffraction maximas

A laser is focused on the hair that is attached to a notecard.
An interference pattern is now projected onto the whiteboard.



Measuring a group of maximum intensities.

A diagram of the experiment with known and calculated values. 
We have solved for the distance, d, between the two source points - the width of the human hair.

Conclusion:

We find that the human hair used is approximately 122.4 micrometers and are now familiar with the order of magnitude of the width of a human hair.

Lenses

This lab explores the effects of placing a converging lense before a real image projected by a filament.  Our goal is to observe the changes in the image produced by the lense as it is moved along the axis between the real image and the projection.

It is necessary to determine the focal length of the lense to be used in the experiment.  In order to do so, we place the lense along a meter stick and focus the sunlight and then note the distance from the lense to the floor (see below).

The focal point of the lense is determined

The lense will now be moved along a meter stick in factors based on the lense's focal lenght.  We will be noting the distance from the object, the image distance, the object height and the image height.  Using the Image height and Object height, we can determine the magnification, M.

A real image is projected through the lense and onto a whiteboard

The results:

Concave and Convex Mirrors

This lab introduces the optical effects of curved mirrors.  We will evaluate how images are formed by both convex and concave mirrors.

Convex mirrors are curved mirrors whose center of curvature reside behind the reflecting surface of the mirror.

Ray Diagram for Convex Mirror

An object before the reflecting surface of a convex mirror will produce a real image.

A Convex Mirror

Myself holding a marker before an convex mirror. 
Note the size of the image

The object is held before the convex mirror.  The image is upright and is smaller than it appears.

Concave Mirrors are curved mirrors whose center of curvature reside in front of the reflecting surface of the mirror.

A ray diagram for a concave mirror

The image created in a concave mirror is a virtual image when the object resides outside the focal point.

A Concave Mirror

The image in a concave mirror.  Note the orientation of the image.