#### Transcript Wave optics

```A water wave is incident on a breakwater as sketched below.
Use Huygen’s principle to make a careful sketch the form of the
waves on the back side of the breakwater.
wave
fronts
A water wave is incident on a
breakwater as sketched
below. Huygen’s principle
has been used to make a
careful sketch of the form of
the waves on the back side of
the breakwater. The dotted
lines represent the peaks of
wave
Huygens waves from the
fronts
lower opening.
Is the interference along
Path I
Path II
(a) constructive
(b) destructive
(c) Not enough information to tell
I
II
III
Path III
The top drawing was used to
determine the angles  at which
dark fringes occur, since any two
waves #1 and #2 which originate
from positions a/2 apart in the slit
are out of phase by /2.
#2
light
intensity
#1
a

incident
light, 
Can the lower drawing be used to
determine the angles  for the
a
bright fringes, where the waves
incident
shown also originate from
light, 
positions a/2 apart?
a/2
(a/2) sin
#2
#1
a/2

(a/2) sin
(a) Yes. Any 2 waves such as #1 and #2 are in phase.
(b) No. A wave originating halfway between #1 and #2
would cancel wave #1.
(c) No. Amplitudes of the waves #1 and #2 are
different.
screen
For a 2 slit interference pattern, rays A and B shown coming from the
2 slits below
P (dark)
light
A

d
B
Screen
  wavelength of the light
If point P at the screen is dark is B’s path length
a) the same as A’s
b) longer by n

2
where n = odd integer
c) longer by n  where n = even integer
2
d) none of the above
For a 2 slit interference pattern, rays A and B shown coming from the
2 slits below
P (dark)
light
A
d

B
Screen
  wavelength of the light
If point P at the screen is dark, B’s path length is longer than A’s path
by approximately
a) d sin 
d) d
b) d cos
c) d tan 
e) none of the above
Newton’s Rings Apparatus
visible  5000  1010 
A B
500nm
d
Optical flat
2nd bright ring
What is the thickness d of the air film for the 2nd bright ring from
the center?
a)

b)

2
4
e) none of the above
c) 
d)
3

4
Two glass slides are touching at one side to make a wedge between
them. The wedge is filled with oil of index of refraction 1.6, the glass
has an index of 1.5. The glass is illuminated from above with light of
wavelength  and viewed from above
ng=1.5
t
no=1.6
P
Which of the following expressions gives the thickness t where the
first bright fringe from point P is observed?
a )t 
d )t 

2

4
b) t 
e)t 

2no

4no
f ) none of the above
c)t  
```