A simple way of observing an interference pattern is to look at a distant light source through a stretched handkerchief or an open umbrella. Explain how this works.

Why is it so much easier to perform interference experiments with a laser than with an ordinary light source?

A soap bubble (n = 1.33) having a wall thickness of 120 nm is floating in air. What is the wavelength of the visible light that is most strongly reflected?

Suppose the film has an index of refraction of $1.36$ and is surrounded by air on both sides. Find the minimum thikkness that will produce constructive interference in the reflected light when the film is illuminated by light of wavelength $500 \mathrm{~nm}$.

Determine the minimum thickness of a soap film ( $n=$ 1.330) that will result in constructive interference of (b) the blue $\mathrm{H}_\gamma$ line $(\lambda=434.0 \mathrm{~nm})$

An electromagnetic wave is traveling straight down toward the center of the Earth. At a certain moment in time the electric field points west. In which direction does the magnetic field point at this moment?

$$\begin{array}{lll}\text { (a) North. } & (d) \text { West. } & (g) \text { Either }(a) \text { or }(b) . \\ (b) \text { South. } & (e) \text { Up. } & (h) \text { Either }(c) \text { or }(d) . \\ (c) \text { East. } & (f) \text { Down. } & (i) \text { Either }(e) \text { or }(f) .\end{array}$$

Certain sunglasses use a polarizing material to reduce the intensity of light reflected from shiny surfaces, such as water or the hood of a car. What orientation of the transmission axis should the material have to be most effective?

Determine the minimum thickness of a soap film ( $n=$ 1.330) that will result in constructive interference of (a) the red $\mathrm{H}_\alpha$ line ( $\lambda=656.3 \mathrm{~nm}$ );

Would it be possible to place a nonreflective coating on an airplane to cancel radar waves of wavelength 3 cm?

Two narrow slits separated by $1.0 \mathrm{~mm}$ are illuminated by $544 \mathrm{~nm}$ light. Find the distance between adjacent bright fringes on a screen $4.0 \mathrm{~m}$ from the slits.

Suppose reflected white light is used to observe a thin, transparent coating on glass as the coating material is gradually deposited by evaporation in a vacuum. Describe some color changes that might occur during the process of building up the thickness of the coating.

(II) A parallel beam of light from a He-Ne laser, with a wavelength 633 nm, falls on two very narrow slits 0.068 mm apart. How far apart are the fringes in the center of the pattern on a screen 3.8 m away?

The waves from a radio station can reach a home receiver by two different paths. One is a straight-line path from the transmitter to the home, a distance of $30.0 \mathrm{~km}$. The second path is by reflection from a storm cloud. Assume that this reflection takes place at a point midway between receiver and transmitter. If the wavelength broadcast by the radio station is $400 \mathrm{~m}$, find the minimum height of the storm cloud that will produce destructive interference between the direct and reflected beams. (Assume no phase changes on reflection.)

For the photoelectric effect, make a table that shows expected observations for a particle theory of light and for a wave theory of light. Circle the actual observed effects.