Ch 8 - Light and Optics

Question 1

Electromagnetic waves

Answer 1

• radio waves - microwaves - IR - visible - UV - Xrays - gamma rays
• transverse waves - field is perpendicular to direction of travel
• radio - long wavelength, low frequency, low energy
• gamma - short wavelength, high frequency, high energy
• all travel at the speed of light
  
  • 3*10^8 m/s = c = frequency * wavelength

Question 2

Visible spectrum

Answer 2

• light with all colors in equal intensity = white
• color of object depends on color of light that it reflects
• blackbody - ideal absorber of all wavelengths (appears black)

Question 3

Reticular Propagation

Answer 3

• light travels in straight line when in homogenous medium

Question 4

Reflection

Answer 4

• rebounding of incident light waves at boundary of a medium
• incident angle = reflection angle
  
  • angle measured from normal line to the surface

Question 5

Real/Virtual

Answer 5

• real - if light actually converges at position of the image
• virtual - if light only appears to be coming from position of image but doesnt converge there
• plane mirrors - always create a virtual image
  
  • no convergence or divergence
  • light remains in front of the mirror, but image appears to be behind the mirror

Question 6

Sperical mirrors

Answer 6

• center of curvature - point equal distance to radius of curvature (center of sphere)
• radius of curvature
• concave - inside the sphere, center of curvature is in front of mirror
  
  • converging
• convex - center of curvature behind the mirror
  
  • diverging
• focal length - distance between focal point and the mirror
  
  • f = r/2
  • o = distance between object and mirror
  • i = distance between image and mirror
  • 1/f = 1/o + 1/i = 2/r
• image distance (i) - if positive than real, means in front of mirror
  
  • if negative than virtual, behind the mirror
• magnification: m = -i/o
  
  • negative magnification - inverted image
  • positive magnification - upright image

Question 7

Convex Mirrors

Answer 7

• aka diverging
• only produces virtual, upright, reduced image
• think of security mirror at convenience store

Question 8

Refraction

Answer 8

• bending of light
• speed through any medium is always less than through a vacuum (3x10^8 m/s)
• n = c/v
  
  • n is index of refraction
  • v is velocity in medium
• Snell’s law
  
  • n₁sin(theta1) = n₂sin(theta2)
• light entering medium with higher index of refraction causes light to bend toward the normal
• critical angle - angle of incidence that causes the angle of refraction to be 90deg and the light runs along interface of 2 media
• total internal reflection - due to incidence angle greater than critical angle
  
  • reflected back into original media

Question 9

Lenses

Answer 9

• refract light
• one focal point for thin lenses
• converging lense - thicker at center
  
  • convex lense
  • farsighted (reading glasses)
  • similar to concave mirror
  • positive r and f
• diverging lens - thinner at center
  
  • concave lense
  • similar to convex mirror
  • nearsighted (distance glasses)
  • negative r and f

Question 10

PRI NVU

Answer 10

positive real inverted

negative virtual upright

• real and inverted from (i) value
  
  • positive than real, opposite side of lens from light
  • negative than virtual, same side of lens as light

Question 11

Power of lense

Answer 11

• (P)
• P = 1/f
• f is focal lenght
• positive in converging
  
  • faresighted
  • hyperopia
  • image converges beyond the retina
• negative in diverging
  
  • nearsighted
  • myopia
  • image converges before the retina

Question 12

Spherical aberration

Answer 12

• blurring of periphery of image
• due to inadequate reflection of parallel beams at edges

Question 13

Multiple lens system

Answer 13

• power is cumulative
  
  • add powers together
• 1/f = 1/f₁ + 1/f₂ +1/f₃
• multiply magnifications

Question 14

Dispersion

Answer 14

• various wavelengths of light seperate from each other
  
  • prism of color
• shorter wavelength are refracted the most
• wavelength of light changes, but frequency remains the same

Question 15

Chromatic aberration

Answer 15

• dispersive effect in a spherical lens
• causes rainbow halo around image
• corrected with coating over lenses

Question 16

diffraction

Answer 16

• spreading of light as it passes through a narrow opening or around an obstacle
• exits narrow slit in an arch instead of a beam

Question 17

Slits and light

Answer 17

• slit-lens system
  
  • lenses between slit and screen
  • alternating dark and bright fringes
• Multiple slits
  
  • interference - displacements of waves add together
  • light through 2 slits interfereces with one another
  • constructive interference is brighter
  • destructive interference is not as bright
• Diffraction gratings - multiple slits in a pattern cause iridescent rainbow
  
  • can also be caused by thin films (due to reflected rays)
    
    • bubbles, oil puddles

Question 18

X ray diffraction

Answer 18

create model of molecules

combined with protein crystallography

analyze protein structure

Question 19

Plane polarized light

Answer 19

• linearly polarized light
• electric fields of all waves oriented in same direction
  
  • determines plane of polarization
• magnetic fields also parallel
• chiral centers cause a specific rotation of plane polarized light
  *

Question 20

Circular Polarization

Answer 20

• uniform aplitude and continuous change in direction
• helical shape propagating wave