Chapter 10: Light and Optics Flashcards
Electromagnetic waves are transverse or longitudinal?
Transverse; they can also travel through a vacuum
Electromagnetic waves consist of what two oscillating fields?
an oscillating electric field and an oscillating magnetic field; the two fields are perpendicular to each other and to the direction of the propagation of the wave
The electromagnetic spectrum is:
the range of frequencies and wavelengths found in electromagnetic waves
The electromagnetic spectrum from lowest energy to highest energy:
radio waves, microwaves, infrared, visible light, ultraviolet, x-rays, and gamma rays
Equation to determine the wavelength or frequency of light traveling in air or a vacuum:
c = fλ
where c is the speed of light and is equal to 3 X 108;
units = m/s
1 angstrom =
1 X 10-10
Electromagnetic waves vary in frequency and wavelength, but in a vacuum, they all travel at the same speed, which is:
the speed of light (3 X 108 m/s)
The visible spectrum ranges from what wavelengths?
380nm (violet) to 760nm (red)
The order of the colors in the visible spectrum:
ROY-G BIV
red (760nm), orange, yellow, green, blue, indigo, violet (380nm)
Rectilinear propagation:
when light travels in a straight line through a single homogenous medium
Theory of geometrical optics describes:
the behavior of light at the boundary of a medium or interface between two media
Reflection is:
the rebounding of incident light waves at the boundary of a medium
Law of Reflection equation:
θ1 = θ2
where θ1 is the incident angle and θ2 is the reflected angle
the angles are always measured from normal (a line perpendicular to the surface of the medium)
An image is real if:
the light converges at the position of the image
An image is virtual if:
the light appears to be coming from the position of the image, but does not actually converge there
Plane mirrors always create what kinds of images?
virtual, upright images the same size as the object since the light does not converge at all
The two types of spherical mirrors:
concave and convex; they both have centers and radii of curvature as well as focal points
Concave mirrors:
converging systems and can produce real, inverted images or virtual, upright images, depending on the placement of the object relative to focus
Convex mirrors:
diverging systems and will only produce virtual, upright images
The focal point of converging mirrors and converging lenses will always be:
positive
The focal point of diverging mirrors and diverging lenses will always be:
negative
Equation to determine the object or image distance from a mirror, focal length, or radius of curvature:
1/o + 1/i = 1/f = 2/r
where o is the distance of the object from the mirror, i is the distance of the image from the mirror, f is the distance from the focal point to the mirror (focal length), and r is the distance between the center of curvature and the mirror (for spherical mirrors)
units = m-1
For spherical mirrors, what does the focal length (f) equal?
f = r/2
For a plane mirror, the mirror equation becomes:
1/o + 1/i = 0
because at any time the object is at the focal point, the reflected rays will be parallels and the image will be at infinity
Equation to find the magnification of an image for both mirrors and lenses:
m = - i/o
where o is the distance of the object from the mirror and i is the distance of the image from the mirror or lens
if the absolute value of m is less than 1, the image is reduced
if the absolute value of m is greater than 1, the object is enlarged
For magnification, if the absolute value of m is greater than 1:
the image is enlarged
For magnification, if the absolute value of m is less than 1:
the image is reduced
Refraction is:
the bending of light as it passes from one medium to another and changes speed
In refraction, the speed of light changes depending on:
the density of the medium; this speed change is what causes diffraction
Equation to determine the index of refraction:
n = c/v
where c is the speed of light in a vacuum (3.8 X 108), v is the speed of light in the given medium, and n is the index of refraction
In regards to refraction, for all mediums besides air, what are v and n equal to?
v < c because the speed of light is slower in any other medium; n > 1
Equation to find the degree of refraction of a light ray upon entering a new medium:
n1sinθ1 = n2sinθ2
theta is always measured with respect to the perpendicular to the boundary
When light enters a medium with a higher index of refraction, it bends toward:
the normal
When lights enters a medium with a lower index of refraction, it bends away from:
the normal
The index of refraction for air:
1
Snell’s law states that:
there is an inverse relationship between the index of refraction and the sine of the angle of refraction (measured from the normal)
Total internal reflection occurs when:
light leaving a medium is instead reflected back inside it; it happens when light moves from a medium with a higher index of refraction to a medium with a lower index of refraction with a high angle of incidence
Critical angle:
the minimal angle of incidence at which total internal reflection occurs for that substance; the critical angle is when the refracted angle equals 90 degrees
Equation to determine the critical angle:
derived from Snell’s Law
sinθc = n2 / n1
When the incident angle is greater than the critical angle:
total internal reflection occurs and the light incident on the boundary will be reflected back into the original material
What do lenses do?
refract light to form images of objects
Thin, bilaterally symmetric lenses have focal points where?
on each side
Convex lenses are:
converging systems and can produce real, inverted images or virtual, upright images (are like concave mirrors)
Concave lenses are:
diverging systems and will only produce virtual, upright images (are like convex mirrors)
When traveling through a lens, how many times does the light refract?
twice; from air to lens and from lens to air
Equation to determine object distance (o), image distance (i), focal length (f), and magnification (m) for lenses:
1/o + 1/i = 1/f
m = -i/o
Equation to determine the focal length in lenses where thickness cannot be ignored:
1/f = (n-1)(1/r1 - 1/r2)
where n is the index of refraction of the lens material, r1 is the radius of the curvature of the first lens surface, and r2 is the radius of curvature of the second lens surface
To simplify sign conventions, think about if the image is on the side it’s supposed to be on or not. Mirrors reflect light back; lenses let light pass though. If the image is on the wrong side:
then the image is a virtual image
Equation to determine the power of a lens:
P = 1/f
where f is the focal length in meters; P is positive for converging lenses and negative for diverging lenses
Lenses in contact definition and equation:
a series of lenses with negligible distances between them (contact lenses). They behave as a single lens.
1/f = 1/f1 + 1/f2 + 1/f3 + …
P = P1 + P2 + P3 + …
Equation to determine the magnification of a system of lenses not in contact:
M = (m1)(m2)(m3)…
Causes and process of dispersion:
depending on the wavelength of the light, it will bend differently when going through a dispersive medium (i.e. a prism). It is when the speed of light varies with wavelength
Diffraction:
the bending and spreading out of light as it passes through a narrow slit; the light emerges from the narrow slit in a wide arc, not a narrow beam
Equation to determine the location of dark fringes due to single-slit diffraction with a lens:
asinθ = nλ (n = 1, 2, 3,…)
where a is the width of the slit, lambda is the wavelength of the incident wave, and theta is the angle made by the line drawn from the center of the lens to the dark fringe and the line perpendicular to the screen
Interference demonstrates:
the wave/particle duality of light
Young’s double-slit experiment shows:
the constructive and deconstructive interference of waves that occur as light passes through a double slit; the interference pattern shows minima and maxima of intensity
Equation to determine the position of maxima on the screen in a double slit experiment:
dsinθ = mλ (m = 0, 1, 2, …)
where d is the distance between the slits, θ is the angle between the center of the slits and the maxima, λ is the wavelength of the light, and m is the integer representing the order
USE SMALL ANGLE APPROXIMATION:
SINθ ≈ TANθ
Equation to determine the position of minima on the screen in a double slit experiment:
dsinθ = (m + 1/2)λ (m = 0, 1, 2, …)
where d is the distance between the slits, θ is the angle between the center of the slits and the maxima, λ is the wavelength of the light, and m is the integer representing the order
USE SMALL ANGLE APPROXIMATION
SINθ **≈ **TANθ
Plane polarized light is:
light in which electric fields of al the waves are oriented in the same direction (their electric field vectors are parallel). Light waves exist in 3D, polarizing it limits its oscillations to only 2D
