Castle Learning Review Assignments

As we prepare for our comprehensive Regents examination in June, it is important to make sure we are up to speed on material covered throughout the entire year.  Toward that end, we will undertake a series of seven Castle Learning review assignments consisting of 50-60 multiple choice questions on each of the major topics we have covered this year.  These topics correspond to the short review podcasts available on iTunes and on our course videos page.  I would recommend viewing the appropriate review lessons before tackling the Castle Learning assignments.  Then, take the Castle Learning assignments with your reference table, the calculator you will use on the Regents exam, and your notebook handy.

Each assignment is worth 50 to 60 points, with second chance correct scores counted for full credit!  These are weighty assignments, with distinct opening and closing dates.  Because these are being provided well in advance of due dates, you should have opportunity to plan your time accordingly.  No credit will be given for late assignments or submissions, regardless of attendance or illness issues.  Assignments and Review Schedule is as follows:

NewImagePlease take these assignments seriously, and be diligent in your planning and submissions.  This is a large portion of our fourth quarter grading, and is an excellent opportunity to put yourself in position for achieving an optimal score on the Regents Physics Exam!

Refraction

When a wave reaches the boundary between media, part of the wave is reflected and part of the wave enters the new medium. As the wave enters the new medium, the speed of the wave changes, and the frequency of a wave remains constant, therefore, consistent with the wave equation, Wave Equation, the wavelength of the wave must change.

Question: When a wave enters a new material, what happens to its speed, frequency, and wavelength?

Answer: Speed changes, frequency remains constant, and wavelength changes.

 

The front of a wave has some actual width, therefore if the wave does not impinge upon the boundary between media at a right angle, not all of the wave enters the new medium and changes speed at the same time. This causes the wave to bend as it enters a new medium in a process known as refraction.

To better illustrate this, imagine you’re in a line in a marching band, connected with your bandmates as you march at a constant speed down the field in imitation of a wave front. As your wavefront reaches a new medium that slows you down, such as a mud pit, the band members reaching the mud pit slow down before those who reach the pit later. Since you are all connected in a wave front, the entire wave shifts directions (refracts) as it passes through the boundary between field and mud!

 

The index of refraction (n) is a measure of how much light slows down in a material. In a vacuum, all electromagnetic waves have a speed of c=3*108 m/s. In other materials, light slows down. The ratio of the speed of light in a vacuum to the speed of light in the new material is known as the index of refraction (n). The slower the wave moves in the material, the larger the index of refraction:

Index of Refraction

 

Question: A light ray traveling in air enters a second medium and its speed slows to 1.71 x 108 m/s. What is the absolute index of refraction of the second medium?

Answer: IndexRSoln

 

 

 

Snell's Law

The amount a light wave bends as it enters a new medium is given by the law of refraction, also known as Snell’s Law. Snell’s Law states that Regents Physics Snell's Law, where n1 and n2 are the indices of refraction of the media, and theta corresponds to the angles of the incident and refracted rays, again measured from the normal. Light bends toward the normal as it enters a material with a higher index of refraction (slower material), and bends away from the normal as it enters a material with a lower index of refraction (slower material).

 

Not only does index of refraction depend upon the medium the light wave is traveling through, it also varies with frequency. Thankfully, its variation is typically fairly small, and the Regents Physics Reference Table even provides you a table of indices of refraction for common materials at a set frequency.

 

Indices of Refraction

 

 

Snell's Law Question

Question: A ray of monochromatic light having a frequency of 5.09 × 1014 hertz is incident on an interface of air and corn oil at an angle of 35° as shown. The ray is transmitted through parallel layers of corn oil and glycerol and is then reflected from the surface of a plane mirror, located below and parallel to the glycerol layer. The ray then emerges from the corn oil back into the air at point P.

Calculate the angle of refraction of the light ray as it enters the corn oil from air.

Answer: Snell's Law Answer

Question: Explain why the ray does not bend at the corn oil-glycerol interface.

Answer: The indices of refraction are the same for corn oil and glycerol (the speed of the wave does not change at the corn-oil / glycerol interface).