PASCO OS-8536 OPTICS TABLE - Manual (Page 15)

11
012-06557A Optics Table
Rotate the Ray Table until the light ray emerging from the Cylindrical
Lens just barely disappears. Hold a piece of white paper next to the edge
of the Ray Table so you can see the light ray.
Just as it disappears, the ray separates into colors. The table is rotated far
enough if the red color has just disappeared.
Use the pencil to trace the edges of the Cylindrical Lens onto the Ray
Table. Mark the point on the table where the light ray is internally re-
flected. Also mark the entrance point of the incident ray and the exit point
of the reflected ray.
Remove the Cylindrical Lens and draw the rays that are incident upon and reflect off the inside flat surface of
the Cylindrical Lens. Measure the total angle between these rays using a protractor. Note that this total angle is
twice the critical angle because the angle of incidence equals the angle of reflection.
Experiment 7: Refraction – Convex and Concave Lenses
EQUIPMENT NEEDED
– Light Source – Optics Bench
– Ray Table and Base – Convex Lens
– Concave Lens – ruler
Purpose
To explore the difference between convex and concave lenses and to determine their focal lengths.
Theory
Parallel rays of light passing through a thin convex lens cross at the focal point of the lens. The focal length is
measured from the center of the lens to the focal point.
Procedure
Mount the Light Source, Ray Table Base, and Ray Table on the Optics Bench. Place the Convex Lens on the
edge of the Ray Table nearest to the Light Source. Shine five light rays from the Light Source straight into the
convex lens. Trace the outline of the lens and trace the incident and transmitted rays. Indicate the incoming and
the outgoing rays with arrows in the appropriate directions.
The place where the five refracted rays cross each other is the
focal point of the lens. Measure the focal length from the cen-
ter of the convex lens to the focal point.
Repeat the procedure for the concave lens. Put the concave
lens about two-thirds of the way across the Ray Table from the
Light Source. Note that the rays leaving the lens are diverging
and they will not cross. After you trace the outline of the lens
and the incident and refracted rays, use a ruler to extend the
outgoing rays straight back through the outline of the lens. The
focal point is where these extended rays cross.
Nest the convex and concave lenses together and place them in
the path of the parallel rays. Trace the rays. What does this tell Double
Convex
Lens
OS-8517
P
A
TTERN
LIGHT
SOURCE
COLOR
TO
REPLACE BULB SEE
INSTR
UCTION MANUAL.
BULB
: 12V
10W G-4
DO NOT
T
O
UCH BULB
WI
TH
FINGERS.
DISCONNECT
PO
WE
R
BEFORE CHAN
GING BULB
. 5 3 1
RA
Y
SLITS
Five parallel rays
Figure 7
Ray
Box
Exit point
Reflected Ray
Total Internal
Reflection
Entrance point
Figure 6.3
2
θ
c