AP Physics 2
Unit 6
Wave Motion and Geometric Optics
Two features common to all
mechanical waves
• A wave is a traveling disturbance
• A wave carries energy from place to place
without transferring matter
Two types of waves
• Transverse – the disturbance is
perpendicular to the direction of the
motion
• Longitudinal – the disturbance is parallel to
the direction of the motion
Wave terminology
•
•
•
•
•
•
Equilibrium position
Crest and trough
Wavelength
Amplitude
Period
Frequency
Importante – the frequency of the
wave is determined by the source.
The speed of the wave is
determined by the medium.
Mathematical Description of a
Transverse wave
Superposition of waves
Reflections of a wave at a fixed and
free end.
Standing waves – demo
The electromagnetic Spectrum – no
medium required
All waves of electromagnetic
spectrum spectrum travel at the
speed of light, c = 2.99 x 108 m/s.
Note the relationship between
wavelength, frequency and energy.
The electromagnetic spectrum
• Radio (AM, FM, TV) > 30 cm
• Microwaves (radar, atomic-molecular research,
m-wave ovens) between 30 cm and 1 mm
• Infrared between 1 mm and 700 nm
• Visible light between 400 nm and 700 nm
• Ultraviolet between 400 nm and 60 nm
• X-rays between 60 nm and 10 EE -4 nm
• Gamma rays between 0.1 nm and 10 EE -5 nm
Electromagnetic waves are
transverse waves composed of
alternating electric and magnetic
fields
Polarization of Light
Let’s look at unpolarized light first
The fence and the rope
Geometric Optics
Wave Fronts and Rays
Reflection of Light
Law of Reflection
Specular (regular) and diffuse
reflection
Is all of the light incident upon
the mirror reflected?
Plane Mirrors
Five Properties of the image of a
Plane Mirror
• Upright
• Same size
• Located as far behind the mirror as the
object is in front of the mirror
• Left to right reversed
• Virtual image
Ray Diagram for a Plane Mirror
Spherical Mirrors (concave –
converging and convex –
diverging)
The focal length and radius of
curvature
Ray diagrams for curved mirrors.
Only two rays are needed to locate
an image
• Any ray drawn parallel to the principal axis is
reflected through the focal point
• Any ray drawn through the focal point is reflected
parallel to the principal axis
• Any ray incident upon the mirror is reflected at
the same angle when measured from the normal
• Any ray drawn through the center of curvature is
reflected upon itself
Six ray diagrams for converging
(concave) mirrors
Only one ray diagram for convex
(diverging mirrors)
The mirror equation and
magnification (and an impressive
proof thrown in for free)
Summary of sign conventions for
curved mirrors
• f is positive for a concave mirror and
negative for a convex mirror
• so is positive for an image located in front
of the mirror (our only concern at this
point)
• si is positive for a real image (in front of the
mirror) and negative for a virtual image
(behind the mirror)
Ex. A 2.00 cm object is placed 7.10 cm from
a concave mirror whose radius of curvature is
10.20 cm. Find the location and size of the
image.
Ex. An object with a height of 1.20 cm is
placed 6.00 cm in front of a concave mirror
with a focal length of 10.0 cm. Find the
location and height of the image.
Ex. An object is placed 66 cm in front of a
convex mirror that has a focal length of
46 cm. Find the image distance and
magnification.