Light
INTRODUCTION
Light is electromagnetic radiation at
wavelengths which the human eye can see.
Visible light is the very narrow band of
wavelengths located to the right of infrared
and to the left of ultraviolet waves. Visible
radiation is emitted by everything from fireflies
to light bulbs to stars, and also by fast-moving
particles hitting other particles. A typical
human eye can see wavelengths from about
380 to 750 nm (nanometers) and in terms of
frequency this corresponds to a band of about 790 – 400 terahertz.
Source: NASA
Isaac Newton was one of the earliest pioneers of the visible spectrum. Newton observed that
when a narrow beam of sunlight strikes the face of glass prism at an angle, some of the beam is
reflected and some passes into and through the glass, emerging as different colored bands.
Newton hypothesized that light was made up of infinitesimally small particles of different
colors, and that the different colors of light moved at
different speeds in transparent matter, with red light
moving more quickly in glass than violet light. The
result is that red light was refracted (bent) less sharply
Color Wavelength Frequency
than violet light as it passed through the prism, creating a
violet 380–450 nm 668–789 THz spectrum of colors. The separation of visible light into its
blue 450–495 nm 606–668 THz different colors is known as dispersion. Each color has a
distinct wavelength in which different wavelengths of
green 495–570 nm 526–606 THz light bend varying amounts upon passing through a
yellow 570–590 nm 508–526 THz prism. Dispersion of visible light produces the colors of
red (R), orange (O), yellow (Y), green (G), blue (B) and
orange 590–620 nm 484–508 THz
violet (V), also referred to as ROY G BIV. As a note,
red 620–750 nm 400–484 THz the color indigo is actually not observed in the spectrum
but is traditionally added to help in the memorization for
Source: Wikipedia
the sequence of colors in the visible light spectrum.
LENSES
Lenses cause rays of light to come to focus. A lens is a grounded
or molded piece of glass, plastic, or other transparent material
with opposite surfaces either or both of which are curved. The
curved surface(s) allow the light rays to be refracted so that they
converge or diverge to form an image.
In the top figure to right, light rays converge passing through a
biconvex lens. In the bottom figure, light rays diverge passing
through a biconcave lens. The label f is the focal point where the
nearly straight rays of light meet after passing through the convex
lens, or reflecting off of a concave lens.
Optics Lab
Purpose:
To understand that the speed of light changes when it encounters a change of
media causing rays to bend and that lenses cause rays of light to come to focus by
building a refracting telescope.
TASK 1: GROUP ACTIVITIES (Understanding the Concepts)
Station 1 – Light through a glass block
Show how light bends when it propagates between different media.
Materials
• 2 laser pointers
• 2 acrylic blocks
1. Point the laser directly at large flat side of acrylic.
2. Move the laser in a semi-circle so that it still points at the same location, but at different
incidence angles.
3. Make observations of the angle inside of acrylic (refracted angle).
a. Describe what happens to the light.
b. Describe refraction.
Station 2 – Three lasers converging at a focal point
Show how the shape of an object creates an incident angle causing light to bend.
Materials
• 3 laser pointers
• 1 acrylic block
1.
2.
3.
4.
•
•
1 large positive lens
Can of spray fog
Set up three laser pointers parallel to each other.
Laser beams will pass through acrylic block and hit screen.
Use spray fog to see the path of the beams.
Make observations of what happens to beams.
a. Describe what happens to the beams through the acrylic block.
5. Repeat for lens.
a. Describe what happens to the beams through the lens.