Chapter 17

Question 1

what is diffraction?

Answer 1

waves after passing through an opening, spread out and fill the space behind the opening

Question 2

what is light?

Answer 2

the nature of light is…

light is a wave and light is a beam of tiny particles, blowing around like the wind

Question 3

what is the speed of light?

Answer 3

v = c = 3.0*10^8
v = fλ

Question 4

what is the visible light spectrum?

Answer 4

400nm - 450nm = violet light
450nm - 500nm = blue light
500nm - 570nm = green light
570nm - 590nm = yellow light
590nm - 610nm = orange light
610nm - 700nm = red light

Question 5

what ere the two models of light?

Answer 5

1. The Ray Model: under some circumstances, light acts like particles travelling in a straight line (large openings/ acts on beam)
2. The Wave Model: Under other circumstances, light acts like a wave (small openings/ diffraction)

Question 6

Interference pattern can be observed from two slits?

Answer 6

bright and dark lines (or fringes)

Δy = fringe spacing

Question 7

what is path difference?

Answer 7

Δr is path difference

Question 8

what is phase difference?

Answer 8

Δφ = 2piΔr/λ

Question 9

If Δr = λ, 2λ, 3λ, 4λ,….. then this is ?

Answer 9

This is constructive interference = mλ

Question 10

If Δr = λ/2, 3λ/2, 5λ/2,…. then this is?

Answer 10

This is destructive Interference = (m+ 1/2)λ

Question 11

How do we solve for bright fringes (double-slit interference)?

Answer 11

Δr = dsinθ = mλ
tanθ = y/L

Question 12

how do we find the position of bright fringes (double-slit interference)?

Answer 12

y = mλL/d 
m = 0, 1, 2, 3,.....

Question 13

how do we find the position of dark fringes (double-slit interference)?

Answer 13

y' = (m + 1/2)λL/d 
m = 0, 1, 2, 3,....

Question 14

what is a diffraction grating?

Answer 14

it is a multi-slit device, the waves emerge from each slit in phase

Question 15

how do we find the angles of bright fringes due to a diffraction grating with slits distance d apart?

Answer 15

dsinθ = mλ m= 0, 1, 2, 3,…..

- solve for sinθ; if sinθ

Question 16

what is spectroscopy?

Answer 16

the science of measuring the wavelengths of atomic and molecular emissions

Question 17

what is single-slit diffraction?

Answer 17

Is diffraction through a tall narrow slit with a slit width of (a)

Question 18

what is Huygen’s principle?

Answer 18

1. each point on a wave front is the source of a spherical wavelet(mini wave that is spherical) that spreads out at the wave speed
2. at a later time, the shape of the wave front is the curve that is tangent to all the wavelets

Question 19

how can we find the angles (in radians) of dark fringes in a single-slit diffraction with a slit width of a?

Answer 19

θp = p(λ/a) p= 1, 2, 3,...
y = pλL/a p= 1, 2, 3,... (position of dark fringes for single-slit diffraction)

Question 20

How do you find the width of the central maximum for a single-slit diffraction grating?

Answer 20

w = 2λL/a

Question 21

what is circular-aperture diffraction?

Answer 21

light diffracts and generates a circular diffraction pattern

Question 22

how do we find the first minimum intensity for a circular-aperture diffraction?

Answer 22

θ1 = 1.22λ/D
w = 2y1 = 2Ltanθ1 = 2.44λL/D (width of central maximum for diffraction from a circular aperture of diameter D)

Question 23

what does resolve mean?

Answer 23

separate out details of an object that is being viewed

Question 24

what is thin-film interference?

Answer 24

1. incidence wave is transmitted through the thin film and the glass
2. Part of the incidence wave reflects from the first surface
3. Part of the transmitted wave reflects from the second surface
4. The two reflected waves overlap and interfere

Question 25

Thin film interference is due to path difference, what are these path differences?

Answer 25

actual: path differences in the distances travelled (just like in double and single slit experiments)
effective: path differences due to passage through different media and phase inversion at a boundary

Question 26

Index of refraction is?

Answer 26

n = c(speed of light)/v(speed of light in the medium)
c = n1v1 = n2v2
n1λ1 = n2λ2
frequency does not change when you transition from different mediums

Question 27

How do we solve thin-film interference problems?

Answer 27

1. draw the path of light rays through the film
2. determine the phase shifts due to reflection
3. Calculate the path difference due to the extra distance travelled by the rays crossing the film
4. Don’t forget to take into account the index of refraction of the film

Question 28

0 and 2 phase inversions?

Answer 28

constructive interference = 2t = mλ/nfilm

destructive interference = 2t = (m+1/2)λ/nfilm

Question 29

1 phase inversions?

Answer 29

always destructive interference

2t = mλ/nfilm or 2t = 1/2λ/nfilm

Question 30

If the ray reflects from a high to low medium that means that there is?

Answer 30

a phase inversion

Question 31

if the ray reflects from a low to high medium that means there is?

Answer 31

no phase inversion