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Student’s name: _________________________ Grade: _______
RAY OPTICS LAB
Objective: To study the ray model of light and its applications in optical
instruments such as mirrors and lens.
Theory: Refer to chapter 34 of Randall D. Knight
Introduction:
The study of light is called optics. We learned that light is a part of
electromagnetic spectrum. Light is a real physical entity, but the nature of light is
elusive. Under some circumstances, light acts like particles traveling in straight
lines. But change the circumstances, and light shows the kind of wave-like
behavior as sound waves or water waves. Change the circumstances yet again,
and light behavior that neither wave-like nor particle-like but has characteristics
of both. There are three models of light:
A light ray is a concept, not a physical thing. Any narrow beam of light, such as
the laser beam, is actually a bundle of many light rays.
A light ray is the line along which light energy flows. Two rays can cross without
disturbing one another. The ray model is an oversimplification of reality but
nonetheless is very useful for study lenses and mirrors.
It’s useful to think of each point on an object as a point source of light rays and
a parallel bundle of rays come from a distant object.
Reflection:
Reflection of light is a familiar, everyday experience. You see your reflection in
the bathroom mirror, in your car’s rearview mirror, from a flat, smooth surface,
etc.
Law of reflection:
– The incident ray and the reflected ray are in the same plane normal to the
surface
– The angle of reflection equals the angle of incidence.
The plane mirror:
Refraction and Snell’s law:
Two things happen when a light ray is incident on a smooth boundary between
two transparent materials, such as the boundary between air and glass:
– Part of the light reflects from the boundary, obeying the law of reflection
(this is how you see reflections from storefront windows)
– Part of the light continues into the second medium. It’s transmitted and the
transmitted ray changes direction as it crosses the boundary (refraction
ray).
Index of refraction (or refractive index) is a value calculated from the ration of
the speed of light in a vacuum to that in a second medium of greater density.
It measures the bending of a ray of light when passing from one medium into
another.
According to Einstein, c is the max speed in universe, so n > 1.
Total internal reflection:
When a ray comes from a higher index of refraction to the boundary with a lower
index of refraction, a total internal reflection phenomenon can be happened.
From the following photo, we can compute the critical angle θc (at which the total
internal reflection happened).
The most important modern application of total internal reflection is the
transmission of light through optical fibers. The light rays pass easily into the
glass fiber, but they then impinge on the inside wall of the glass tube at an angle
of incidence almost 90o, bigger than the critical angle, so the light beam remains
inside the glass fiber and can be detected at the other end.
APPLICATION OF RAY OPTICS
QUESTIONS
(20 points)
1. A laser beam in air is incident on a water at an angle of 50 o with respect to
the normal. Index of refraction of air is 1.02 and of water is 1.33. What is
the angle of refraction? Show your works. Open this Snell’s law simulation
drag the light source to create an incident angle of 50 o to verify your
answer. Insert your screenshot here.
2. A 9-cm tall object is 30 cm in front of a convex mirror with focal length of
-20 cm. Is the image real or virtual? Is the image upright or inverted?
Calculate the position and height of the image? Show your works. Open
this simulation
to verify your answer. Insert your screenshot here.
3. A 9-cm tall object is 30 cm in front of a concave mirror with focal length
of 20 cm. Is the image real or virtual? Is the image upright or inverted?
Calculate the position and height of the image? Show your works. Open
this simulation
to verify your answer. Insert your screenshot here.
4. A 9-cm tall object is 50 cm in front of a converging lens (convex lens) with
focal length of 20 cm. Is the image real or virtual? Is the image upright or
inverted? Calculate the position and height of the image? Show your
works. Open this simulation
to verify your answer. Insert your screenshot here.
5. A 9-cm tall object is 40 cm in front of a diverging lens (concave lens) with
focal length of -20 cm. Is the image real or virtual? Is the image upright or
inverted? Calculate the position and height of the image? Show your
works. Open this simulation
to verify your answer. Insert your screenshot here.
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