purpose of this minilab
DESCRIPTION
Purpose of this Minilab. Apply the basics of ray tracing to learn about reflection and refraction of light. Activity 1: Light Reflection at Plane Surfaces. Angle of incidence. Angle of reflection. Index of refraction of the two materials. n i. n t. Angle of transmission (refraction). - PowerPoint PPT PresentationTRANSCRIPT
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
i
r
Mirror
Optics 1 - Activities with Light Rays
Measuring refraction
0
45
45
90
90
135
180
135
Light Source
Polar graphpaper
i
t
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
crit
Semicircularlens
Light musthit the centerof the flat side
Optics 1 - Activities with Light Rays
Snell’s Law for Critical Angle
90sinsin aircriticalplastic nn
criticalplasticn
sin1
=1
Optics 1 - Activities with Light Rays
Light beam displacement by plane parallel plate
Light Source
i
t
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
i
t
d• Trace light ray on polar graph paper.• Outline location of rectangular plastic on paper.• Measure angles i and t.• 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 i (and corresponding t 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
1111RR
nf
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
1111RR
nf
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
25.15
)2(65.05
151165.11111
21
cmf 4
Optics 1 - Activities with Light Rays
The Imaging Equation for Lenses and Mirrors
fPS111
S: Object DistanceP: Image Distancef: Focal Length
2Rf For Mirrors: where R = Radius of Mirror
RPS211
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