Midterm I

Question 1

What are the two types of radiation based on radiation effect?

Answer 1

Ionizing Radition - particle and EM radiation with ultraviolet or shorter wavelengths

Non-Ionizing Radiations - visible light and lower wavelengths, sound and ultrasound

Question 2

What is the formula for attenuation of radiation?

Answer 2

J = J₀⋅e^−μx

Where J is attenuated radiation, J_{<strong>0</strong>}is initial radiation, μ is a constant for the attenuating material and x is the thickness of the material.

Question 3

What is the difference between transverse and longitudinal waves?

Answer 3

**Transverse **- wave oscillates perpendicular to its direction of travel

Longitudinal - wave oscillates in the same direction as its travel

Question 4

What are the two types of waves categorized by source?

Answer 4

Mechanical - elastic disturbance through elastic medium

Electromagnetic - electronic disturbance propagating through space (vacuum)

Question 5

What are the 3 types of waves according to their dimension of propagation?

Answer 5

one-dimensional - rope

surface - pond ripples

spatial - sound

Question 6

What does the Huygens-Fresnel principle state?

Answer 6

Every point in a wavefront is a source of further waves

Question 7

Describe the image in the retina.

Answer 7

Real, diminished, inverted

Question 8

What is Wien’s Displacement Law?

Answer 8

the wavelength distribution of thermal radiation from a black body at any temperature has essentially the same shape as the distribution at any other temperature, except that each wavelength is displaced on the graph

Question 9

What is Snell’s Law, both as it relates to wave velocity and index of refraction?

Answer 9

Snell’s law states that the ratio of the sines of the angles of incidence and refraction is equivalent to the ratio of phase velocities in the two media, or equivalent to the reciprocal of the ratio of the indices of refraction:

• Can be rearranged as V₁/sin θ₁ = V₂/sin θ_{<strong>2</strong>} or as

n₂ x sin θ₂ = n₁ x sin θ₁

Question 10

What is the trigonometric mnemonic for what sine, cosine and tangent mean?

Explain it.

Answer 10

SOH CAH TOA

Sine = Opposite/Hypotenuse

Cosine = Adjacent/Hypotenuse

Tangent = Opposite/Adjacent

Question 11

What is the critical angle?

Why does it exist?

Answer 11

The **critical angle **is the angle of incidence at which the angle of refraction is 90 degrees (and thus the refracted ray travels along the interface of the 2 media).

• Critical angles exist because when light moves from a slow medium to a fast medium, its angle of refraction will always be greater than its angle of incidence.

Question 12

How does one find the critical angle, past which total internal reflection will occur, when shining light from a slow to a fast medium?

Answer 12

n_i× sin θ_i = n_r

Same as Snell’s law, but sin θ_r = 1 (and is therefore left out) because the angle of refraction (θ_r) is 90 degrees.

Question 13

According to Abbe’s formula, how is the resolution limit of a microscope decreased?

Answer 13

by decreasing wavelength of illuminating light and increasing aperature angle of the objective lens

Question 14

How will decreasing the refractive index affect its optical power? focal length?

Answer 14

Will decrease optical power and increase focal length

Question 15

What are some of the manifestations of light’s wave nature and when do they occur?

Answer 15

Light acts as a wave during propagation:

- diffraction

- interference

- polarization

Question 16

What are some of the manifestations of light’s particle nature and when do they occur?

Answer 16

Light acts as a particle during interactions:

- photoelectric effect

- refraction

- excitation/ionization

- Compton scatter

- pair production

Question 17

What is the photoelectric effect?

Answer 17

the effect of electron emission from many metals that is caused when light is shined upon them

Question 18

What are the particle vs. non particle radiations?

Answer 18

Alpha radiation and Beta radiation are particle radiations.

Gamma radiation is non-particle.

Question 19

Describe Alpha radiation.

Answer 19

An atom gives off 2 protons and 2 neutrons, releasing a Helium atom.

• the atom therefore loses 4 AMUs and 2 atomic numbers

Question 20

Describe the two types of Beta radiation.

Answer 20

Positron Emission (B+ decay)

• a proton emits its positive charge as a positron, but keeps its mass, becoming a neutron
• atom keeps its mass but loses 1 atomic number

Electron Emission (B- decay)

• a neutron loses an electron and becomes a proton
• atom keeps its mass and gains 1 atomic number

Question 21

Describe Gamma radiation.

Answer 21

Unlike alpha and beta, there is no major change in subatomic constituents.

Neutrons and protons simply bundle tighter together in the nucleus, increasing the energy state of the atom and emitting radiation.

Question 22

What is optical power?

What is is measured in?

Describe its relationship to focal length.

Answer 22

Optical power is the light ray converging power of a lens.

It is measured in diopters or 1/m.

It is inversely proportional to focal length.

(A “stronger” lens of greater optical power converges rays a a closer distance or shorter focal length.)

Question 23

What is the lens makers equation?

Answer 23

D = (n₁₂ - 1)(1/R₁ + 1/R₂)

Question 24

What is the lens equation?

Answer 24

1/f = 1/i + 1/o

Question 25

What is the equation which relates image size and distance to object size and focal length?

Answer 25

O/f = (O + I)/i

Question 26

How is magnification determined?

Answer 26

Image size or distance divided by object size or distance.

M = I/O = i/o

Question 27

What does a negative image distance indicate?

Answer 27

a virtual image on the same side of the lens as the object

Question 28

What does a negative image size indicate?

Answer 28

an upright, virtual image

Question 29

How is absolute refractive index determined?

Answer 29

n₁= C/C₁

abs. refractive index = speed of light in vacuum over speed of light in medium

Question 30

How can the critical angle be determined?

Answer 30

by setting the incident angle at 90 degrees

Question 31

How can the angle of total internal reflection be determined?

Answer 31

by setting the refracted angle to 90 degrees

Question 32

What is Fermat’s principle?

Answer 32

Rather than taking the shortest distance between two points, light takes the route which would take the least time.

In other words, it travels as long as possible in the less optically dense medium.

Question 33

How can electron volts be determined from wavelength?

Answer 33

• convert wavelength from nm to m
• use E = hf = h(c/λ) to get Joules
• convert to eV with 1 eV = 1.6x10^-19 J

Question 34

How can λ causing photochemical effect be determined if given required energy in kJ/mol?

Answer 34

• convert to J/mol
• divide by avogadro’s number to get J
• use E = h * (C/λ) to find wavelength