AP Physics 2 Unit 7
Refraction and Physical Optics
Refraction and Lenses
Refraction – the bending of light as it
passes between two media with
different optical densities
The index of refraction
𝑐
𝑛=
𝑣𝑚
Ex. The index of refraction for a diamond
is 2.42. What is the wavelength of green
light in a diamond if the frequency of
light in air is 5.45 x 1014 Hz?
Snell’s Law – “Proof Ahoy”
Ex. Light is incident in air (nair = 1.00) upon
an equilateral crown glass prism (ng = 1.52)
at an angle of 45.0⁰ to one face. Calculate
the angle at which the light emerges from
the opposite face.
Total Internal Reflection
Ex. A ray of light in a diamond (n = 2.42)
strikes an interface at 28⁰. Will the beam of
light enter the air or will it be reflected
internally? Will the beam of light be
reflected internally if the diamond is
surrounded by water (nw = 1.33)?
Applications of total internal reflection
Dispersion of Light
Lenses
Two types of lenses
Images formed by converging lenses
Image formed by a diverging lens
A familiar friend
Sign conventions for lenses:
• f is positive for converging lenses and
negative for diverging lenses
• so is positive when light is reflected from
the object (a real object)
• si is positive when it is behind the lens (real
image) and negative when it is in front of
the lens (virtual image)
Physical Optics
First, what is diffraction of light?
The trumpet and the spotlight
outside of the door.
Huygen’s Principle
Linear Superposition
Young’s Double Slit Experiment
and Wave Properties of light
Bright and dark fringes, also known
as maxima and minima also known
as bright and dark bands
Position of the maxima and minima
“Order in the fringe!”
Intensity of the maxima and minima
Two equations for double-slit interference
𝑚λ = 𝑑 sin 𝜃
and
𝑚λ𝐿
𝑥𝑚 =
𝑑
Ex. The distance between two slits is
1.20 x 10 –4 m. An interference pattern is
projected onto a screen 2.75 m away. Find the
distance on the screen between the central
maximum and and the third order maximum.
Single slit interference
Diffraction grating
The electromagnetic Spectrum
All wave of e-m spectrum travel at the
speed of light c (2.99 x 108 m/s, like really,
really fast). Note the relationship between
wavelength, frequency and energy.
E-m spectrum
• Radio (AM, FM, TV) > 30 cm
• Microwaves (radar, atomic-molecular research,
microwave 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 10-4 nm
• Gamma rays between 0.1 nm and 10-5 nm
Polarization of Light
Let’s look at unpolarized light first
The fence and the rope