Optics 1 - Activities with Light Rays Purpose of this Minilab Apply the basics of ray tracing to...
Transcript of Optics 1 - Activities with Light Rays Purpose of this Minilab Apply the basics of ray tracing to...
Optics 1 - Activities with Light Rays
Purpose of this Minilab
• Apply the basics of ray tracing to learn about reflection and refraction of light.
Optics 1 - Activities with Light Rays
Activity 1: Light Reflection at Plane Surfaces
i r
t
ni
nt
Index of refractionof the two materials
Angle of incidence Angle of reflection
Angle of transmission (refraction)
Optics 1 - Activities with Light Rays
ir Law of Reflection:
Snell’s Law of Refraction: ttii nn sinsin
Incident, reflected, and transmitted ray lie in one plane.
…..the laws….
.
Optics 1 - Activities with Light Rays
Checking the law of reflection with a plane mirror
0
45
45
90
90
135
180
135
Light Source
Polar graphpaper
Qi
Qr
Mirror
Optics 1 - Activities with Light Rays
Measuring refraction
0
45
45
90
90
135
180
135
Light Source
Polar graphpaper
Qi
Qt
Semicircularlens
Light musthit the centerof the flat side
Use Snell’slaw to determinenplastic.
nplastic
Optics 1 - Activities with Light Rays
Measuring angle of total internal reflection
0
45
45
90
90
135
180
135
Light Source
Polar graphpaper
Qcrit
Semicircularlens
Light musthit the centerof the flat side
Optics 1 - Activities with Light Rays
Snell’s Law for Critical Angle
90sinsin aircriticalplastic nn
criticalplasticn
sin
1
=1
Optics 1 - Activities with Light Rays
Light beam displacement by plane parallel plate
Light Source
Qi
Qt
dt
Optics 1 - Activities with Light Rays
0
45
45
90
90
135
180
135
Polar graphpaper
Light beam displacement by plane parallel plate
Light Source
Qi
Qt
d• Trace light ray on polar graph paper.• Outline location of rectangular plastic on paper.• Measure angles Qi and Qt.• Measure widths d and t.
t
Let the beam hit therectangle in centerof the polar paper
Optics 1 - Activities with Light Rays
Light beam displacement by plane parallel plate
t
ii n
tdcos
cos1sin
• Use one incident angle Qi (and corresponding Qt and d and t) calculate n.
• Use this calculated n to predict the displacement d for a different incident angle. (Hint: You will also need to use Snell’s Law for this calculation.)
• Verify experimentally d for the new angle.
Optics 1 - Activities with Light Rays
180
Polar graphpaper
R0
45
45
90
90
135
135
Move mirror untilcurvature matchesthe curvature onpolar graph paper.then measure Ras shown.
Activity 2: Reflection and Refraction at Spherical Surfaces – Getting the Radius of Curvature
Optics 1 - Activities with Light Rays
Finding the focal point of the concave mirror
Regular graph paper: Trace the rays and determine f.
Light Source
parallel rays
f
Optics 1 - Activities with Light Rays
Finding the focal point of the convex mirror
Regular graph paper: Trace the rays and determine f.
Light Source
parallel rays
f
Extend the light rays backward to where they seem to come from.
Virtual image(isn’t reallythere).
Optics 1 - Activities with Light Rays
Imaging with the convex mirror
Regular graph paper: Trace the rays and determine f.
P
Light Source
Semicircular or Circular lens
Here is ourobject point
S
Optics 1 - Activities with Light Rays
Thin Lens Equation (how to calculate focal length from the radii of a lens and it’s index of refraction)
21
111
1
RRn
f
Each lens has two interface with the air (#1 and #2).Interface #1 is the one that is encountered by the light when entering the lens.Interface #2 is the one that is encountered by the light when exiting the lens.
Interface #1 hasradius R1.
Interface #2 hasradius R2.
Optics 1 - Activities with Light Rays
Thin Lens Equation (how to calculate focal length from the radii of a lens and it’s index of refraction)
21
111
1
RRn
f
Sign rules for R1:
R1 positive R1 negative
R2 negativeR2 positive
Optics 1 - Activities with Light Rays
Example of using the lens equation
A double concave lens (concave on interface #1 and also on #2)with both radii being 5cm and the index of refraction n=1.65 :
R1 = - 5 cm and R2 = + 5 cm
cmcmcmcmRR
nf 5
25.1
5
)2(65.0
5
1
5
1165.1
111
1
21
cmf 4
Optics 1 - Activities with Light Rays
The Imaging Equation for Lenses and Mirrors
fPS
111
S: Object DistanceP: Image Distancef: Focal Length
2
Rf For Mirrors: where R = Radius of Mirror
RPS
211
Optics 1 - Activities with Light Rays
Sign Rules For Lenses and Mirrors
Convex Lens: +Concave Lens: -Convex Mirror: -Concave Mirror: +
f
Real objects: S is positiveVirtual objects: S is negative
Real images: P is positiveVirtual images: P is negative
Means: a positive number
Most objects are real.
Optics 1 - Activities with Light Rays
Example of signs for f, S, and P
P
Light Source
S
Real object
Virtual image
positive negative
Convex mirror: f is negative
Optics 1 - Activities with Light Rays
Using the Desk Lamp
Dimmer
Lamp Plug (black) must be pluggedinto dimmer plug.Dimmer plug (white) must be pluggedinto power outlet.
On/Offswitchof lamp