Chapter 10: Light and Optics

Question 1

Electromagnetic waves are transverse or longitudinal?

Answer 1

Transverse; they can also travel through a vacuum

Question 2

Electromagnetic waves consist of what two oscillating fields?

Answer 2

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

Question 3

The electromagnetic spectrum is:

Answer 3

the range of frequencies and wavelengths found in electromagnetic waves

Question 4

The electromagnetic spectrum from lowest energy to highest energy:

Answer 4

radio waves, microwaves, infrared, visible light, ultraviolet, x-rays, and gamma rays

Question 5

Equation to determine the wavelength or frequency of light traveling in air or a vacuum:

Answer 5

c = fλ

where c is the speed of light and is equal to 3 X 10⁸;

units = m/s

Question 6

1 angstrom =

Answer 6

1 X 10^-10

Question 7

Electromagnetic waves vary in frequency and wavelength, but in a vacuum, they all travel at the same speed, which is:

Answer 7

the speed of light (3 X 10⁸ m/s)

Question 8

The visible spectrum ranges from what wavelengths?

Answer 8

380nm (violet) to 760nm (red)

Question 9

The order of the colors in the visible spectrum:

Answer 9

ROY-G BIV

red (760nm), orange, yellow, green, blue, indigo, violet (380nm)

Question 10

Rectilinear propagation:

Answer 10

when light travels in a straight line through a single homogenous medium

Question 11

Theory of geometrical optics describes:

Answer 11

the behavior of light at the boundary of a medium or interface between two media

Question 12

Reflection is:

Answer 12

the rebounding of incident light waves at the boundary of a medium

Question 13

Law of Reflection equation:

Answer 13

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)

Question 14

An image is real if:

Answer 14

the light converges at the position of the image

Question 15

An image is virtual if:

Answer 15

the light appears to be coming from the position of the image, but does not actually converge there

Question 16

Plane mirrors always create what kinds of images?

Answer 16

virtual, upright images the same size as the object since the light does not converge at all

Question 17

The two types of spherical mirrors:

Answer 17

concave and convex; they both have centers and radii of curvature as well as focal points

Question 18

Concave mirrors:

Answer 18

converging systems and can produce real, inverted images or virtual, upright images, depending on the placement of the object relative to focus

Question 19

Convex mirrors:

Answer 19

diverging systems and will only produce virtual, upright images

Question 20

The focal point of converging mirrors and converging lenses will always be:

Answer 20

positive

Question 21

The focal point of diverging mirrors and diverging lenses will always be:

Answer 21

negative

Question 22

Equation to determine the object or image distance from a mirror, focal length, or radius of curvature:

Answer 22

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

Question 23

For spherical mirrors, what does the focal length (f) equal?

Answer 23

f = ^r/₂

Question 24

For a plane mirror, the mirror equation becomes:

Answer 24

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

Question 25

Equation to find the magnification of an image for both mirrors and lenses:

Answer 25

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

Question 26

For magnification, if the absolute value of m is greater than 1:

Answer 26

the image is enlarged

Question 27

For magnification, if the absolute value of m is less than 1:

Answer 27

the image is reduced

Question 28

Refraction is:

Answer 28

the bending of light as it passes from one medium to another and changes speed

Question 29

In refraction, the speed of light changes depending on:

Answer 29

the density of the medium; this speed change is what causes diffraction

Question 30

Equation to determine the index of refraction:

Answer 30

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

Question 31

In regards to refraction, for all mediums besides air, what are v and n equal to?

Answer 31

v \< c because the speed of light is slower in any other medium; n \> 1

Question 32

Equation to find the degree of refraction of a light ray upon entering a new medium:

Answer 32

n₁sinθ₁ = n₂sinθ₂ theta is always measured with respect to the perpendicular to the boundary

Question 33

When light enters a medium with a higher index of refraction, it bends toward:

Answer 33

the normal

Question 34

When lights enters a medium with a lower index of refraction, it bends away from:

Answer 34

the normal

Question 35

The index of refraction for air:

Answer 35

1

Question 36

Snell's law states that:

Answer 36

there is an inverse relationship between the index of refraction and the sine of the angle of refraction (measured from the normal)

Question 37

Total internal reflection occurs when:

Answer 37

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

Question 38

Critical angle:

Answer 38

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

Question 39

Equation to determine the critical angle:

Answer 39

derived from Snell's Law sinθ_c = n₂ / n₁

Question 40

When the incident angle is greater than the critical angle:

Answer 40

total internal reflection occurs and the light incident on the boundary will be reflected back into the original material

Question 41

What do lenses do?

Answer 41

refract light to form images of objects

Question 42

Thin, bilaterally symmetric lenses have focal points where?

Answer 42

on each side

Question 43

Convex lenses are:

Answer 43

converging systems and can produce real, inverted images or virtual, upright images (are like concave mirrors)

Question 44

Concave lenses are:

Answer 44

diverging systems and will only produce virtual, upright images (are like convex mirrors)

Question 45

When traveling through a lens, how many times does the light refract?

Answer 45

twice; from air to lens and from lens to air

Question 46

Equation to determine object distance (o), image distance (i), focal length (f), and magnification (m) for lenses:

Answer 46

¹/_o + ¹/_i = ¹/_f m = ^-i/_o

Question 47

Equation to determine the focal length in lenses where thickness cannot be ignored:

Answer 47

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

Question 48

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:

Answer 48

then the image is a virtual image

Question 49

Equation to determine the power of a lens:

Answer 49

P = ¹/_f where f is the focal length in meters; P is positive for converging lenses and negative for diverging lenses

Question 50

Lenses in contact definition and equation:

Answer 50

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 + ...

Question 51

Equation to determine the magnification of a system of lenses not in contact:

Answer 51

M = (m₁)(m₂)(m₃)...

Question 52

Causes and process of dispersion:

Answer 52

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

Question 53

Diffraction:

Answer 53

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

Question 54

Equation to determine the location of dark fringes due to single-slit diffraction with a lens:

Answer 54

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

Question 55

Interference demonstrates:

Answer 55

the wave/particle duality of light

Question 56

Young's double-slit experiment shows:

Answer 56

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

Question 57

Equation to determine the position of maxima on the screen in a double slit experiment:

Answer 57

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**

Question 58

Equation to determine the position of minima on the screen in a double slit experiment:

Answer 58

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**

Question 59

Plane polarized light is:

Answer 59

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