3B Scientific Optical Bench U, 1200 mm - Manual (Page 14)

14
•
Use the lens to generate a parallel beam.
•
The incidenting rays are reflected so that they all
pass through and converge at a single point F. This
point is the focal point of the mirror.
•
Repeat the experiment with converging and diverg-
ing light beams.
•
Result: a concave mirror causes the rays to converge.
•
Rotate the optical disc by 180° so that the incident
rays are reflected by the convex mirror. Carry out
the same procedural steps as stated above.
•
A convex mirror causes the rays to diverge.
Experiment 5: Snell's law of refraction
5.1 Equipment:
•
Optical bench U17150
•
Experimental lamp U17140
•
Object holder, shaft-mounted U17000
•
Diaphragm with single slit from U17040
•
Concave lens f = +150 mm U17108
•
Optical disc U17128
•
Semi-circular body from U17128
•
3 optical riders 75 mm U17160
•
1 optical rider 30 mm U17161
•
Plug-in power supply unit U13900
5.2 Set up
•
Place the experimental lamp horizontally on the
rail at the 10 cm position.
•
Place the object holder with single slot diaphragm
horizontally on the rail at the 20 cm position.
•
Place the concave lens at the 25 cm position.
•
Mount the optical disc with semi-circular body on
the small rider at the 40 cm position.
5.3 Procedure
•
Fasten the semi-circular body on the optical disc
on the 90°-90° line so that the plane side is facing
the light source.
•
Adjust the height of the disc so that the incident-
ing light ray propagates along the 0° line and is
incident at the precise center of the semicircular
body. The ray of light then propagates uninterrupt-
ed along the 0° line.
•
When the disc is rotated, the light ray is refracted
toward the normal at the point of incidence.
•
The disc is now rotated by 180° so that the convex
disc is facing the light source. The light ray is now
refracted away from the normal at the point of in-
cidence.
•
When the light ray passes from one medium with
the refractive index n
1
to another medium with the
refractive index n
2
its directional change is deter-
mined by Snell's law of refraction:
sin
α
/ sin ß = constant or sin
α
/ sin ß = n
2
/ n
1
α
is the angle of incidence in medium n
1
and ß is
the angle of refraction in medium n
2
.
•
The bigger the angle of incidence is, the larger the
angle of refraction becomes. If n
1
< n
2
, there is a
critical angle
α
. At this angle the refracted ray of
light is refracted along the interface between two
media. If the angle of incidence is greater than the
critical angle, then there is no longer any refrac-
tion and all light is reflected. This case is referred
to as total internal reflection.
Experiment 6: Refraction in a plane-parallel plate
6.1 Equipment:
•
Optical bench U17150
•
Experimental lamp U17140
•
Object holder shaft-mounted U17000
•
Diaphragm with single slit from U17040
•
Concave lens f = +150 mm U17108
•
Optical disc U17128
•
Trapezoidal body from U17128
•
3 Optical rider 75 mm U17160
•
1 Optical rider 30 mm U17161
•
Plug-in power supply unit U13900
6.2 Set up
•
Place the experimental lamp horizontally on the
rail at the 5 cm position.
•
Set up the object holder including diaphragm with
single slit at the 20 cm position.
•
Place the concave lens at the 25 cm position.
•
Set up the optical disc with trapezoidal body on
the small optical rider at the 40 cm position.