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INTERFERENCE

1.

A sheet of glass having an index of refraction of 1.50 is to be coated with a film of material having a refractive index of 1.60 such that green light (wavelength = 525 nm) is preferentially transmitted.

(a): What is the minimum thickness of the film that will achieve the desired result?
(b): Why are other parts of the visible spectrum not also preferentially transmitted?
(c): Will the transmission of any colors be sharply reduced?

2.

A pefectly flat piece of glass (n = 1.4) is placed over a perfectly flat piece of black plastic (n = 1.25) as shown at upper right. They touch at A. Light of wavelength 550 nm is incident normally from above. The location of the dark fringes in the reflected light is shown in the sketch at lower right.

(a): How thick is the space between the glass and the plastic at B?
(b): Water (n = 1.33) seeps into the region between the glass and plastic. How many dark fringes are seen when all the air has been displaced by water?

(The straightness and equal spacing of the fringes is an accurate test of the flatness of the glass.)

3.

Light of wavelength 600 nm is incident normally on three parallel narrow slits separated by 0.60 mm. Sketch the intensity pattern observed on a distant screen as a function of angle $\theta$ for the range of values $0 \le \theta \le 0.0040$ radians.

4.

The figure shows the intensity pattern produced by light passing through an opaque foil with N narrow slits 0.3 mm apart and falling on a screen parallel to the foil 3 m distant.

(a): What wavelength of light is being used?
(b): How many slits were there?

(Neglect the finite widths of the slits; this is an interference problem, not a diffraction problem.)

$\begin{figure} \epsfysize 2.0in \mbox{\epsfbox{/home/jess/P120/PS/n-slit_pattern.ps} } \end{figure}$

5.

A phase synchronized linear array of 6 radiotelescopes separated by 40 km operates on a wavelength of 25 cm.

(a): What angular separation of distant sources can it resolve? Please give your answer in arc seconds.
(b): If it ``looks at'' a source 800 light years away, what is the source linear resolution compared to the Sun-Jupiter distance?

Next: INTERFERENCE & DIFFRACTION Up: Old P120 Homework Questions Previous: MORE SOUND