== Lecture 14: Chapters 34 (Young's Double Slit) and Section 35-11 (Polarization) ==


== Gone fishing, 1 ==

To shoot a fish with a gun, how should you aim?

<<c>>
<<lia(fishing_1.png, align = center)>>
<<c(1)>>

 A. aim directly at the image
 A. aim slightly above
 A. aim slightly below

Ans: C.  Due to Snell's law, the fish looks higher than it really is.

== Gone fishing, 2 ==

To shoot a fish with a '''laser''' gun, how should you aim?

<<c>>
<<lia(fishing_2.png, align = center)>>
<<c(1)>>

 A. aim directly at the image
 A. aim slightly above
 A. aim slightly below

Ans: A.

== Superposition ==

<<c>>
<<lia(superposition.png, align = center, width = 50%)>>
<<c(1)>>

Ans: 3.

== Phase difference ==

The two waves shown are

<<c>>
<<lia(phasediff.png, align = center)>>
<<c(1)>>

  A. out of phase by $\pi$.
  A. out of phase by $\pi / 2$.
  A. out of phase by $\pi / 4$.
  A. in phase.

Ans: B.  One wavelength corresponds to $2\pi$.  Quarter wave length difference here.

== Young's double slit experiment ==

An interference pattern is seen from two slits.  Now, cover one slit with glass, introducing a phase difference of $\pi$ (180$^\circ$; half wavelength) at the slits.  How is the pattern altered?

<<c>>
<<lia(double_slit.png, align = center)>>
<<c(1)>>

  A. pattern vanishes.
  A. pattern expands.
  A. bright and dark spots are interchanged.
  A. no change at all.

Ans: C.  Oveall phase difference is what matters.

== Young's double slit experiment ==

In a double slit experiment, if the wavelength of the light is increased, the interference pattern will

  A. spread out.
  A. shrinks together.
  A. stays the same.
  A. disappears.

Ans: A.  $d\sin \theta = m \lambda$.  With $d,m$ fixed, bigger $\lambda$ means bigger $\theta$.