### Conceptual Questions

### 4.1 Single-Slit Diffraction

As the width of the slit producing a single-slit diffraction pattern is reduced, how will the diffraction pattern produced change?

Compare interference and diffraction.

If you and a friend are on opposite sides of a hill, you can communicate with walkie-talkies but not with flashlights. Explain.

What happens to the diffraction pattern of a single slit when the entire optical apparatus is immersed in water?

In our study of diffraction by a single slit, we assume that the length of the slit is much larger than the width. What happens to the diffraction pattern if these two dimensions were comparable?

A rectangular slit is twice as wide as it is high. Is the central diffraction peak wider in the vertical direction or in the horizontal direction?

### 4.2 Intensity in Single-Slit Diffraction

In Equation 4.4, the parameter $\beta $ looks like an angle but is not an angle that you can measure with a protractor in the physical world. Explain what $\beta $ represents.

### 4.3 Double-Slit Diffraction

Shown below is the central part of the interference pattern for a pure wavelength of red light projected onto a double slit. The pattern is actually a combination of single- and double-slit interference. Note that the bright spots are evenly spaced. Is this a double- or single-slit characteristic? Note that some of the bright spots are dim on either side of the center. Is this a single- or double-slit characteristic? Which is smaller, the slit width or the separation between slits? Explain your responses.

### 4.5 Circular Apertures and Resolution

The resolving power of refracting telescope increases with the size of its objective lens. What other advantage is gained with a larger lens?

The distance between atoms in a molecule is about ${10}^{\mathrm{-8}}\phantom{\rule{0.2em}{0ex}}\text{cm}$. Can visible light be used to “see” molecules?

A beam of light always spreads out. Why can a beam not be created with parallel rays to prevent spreading? Why can lenses, mirrors, or apertures not be used to correct the spreading?

### 4.7 Holography

How can you tell that a hologram is a true three-dimensional image and that those in three-dimensional movies are not?

If a hologram is recorded using monochromatic light at one wavelength but its image is viewed at another wavelength, say $10\%$ shorter, what will you see? What if it is viewed using light of exactly half the original wavelength?

What image will one see if a hologram is recorded using monochromatic light but its image is viewed in white light? Explain.