Chapter 33: Q. 7 (page 954)
Narrow, bright fringes are observed on a screen behind a diffraction grating. The entire experiment is then immersed in water. Do the fringes on the screen get closer together, get farther apart, remain the same, or disappear? Explain.
The edges of the fringes are getting closer to each other.
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Light of wavelength passes though two slits separated by and is observed on a screen behind the slits. The location of the central maximum is marked on the screen and labeled
a. At what distance, on either side of , are the bright fringes?
b. A very thin piece of glass is then placed in one slit. Because light travels slower in glass than in air, the wave passing through the glass is delayed by in comparison to the wave going through the other slit. What fraction of the period of the light wave is this delay?
c. With the glass in place, what is the phase difference between the two waves as they leave the slits?
d. The glass causes the interference fringe pattern on the screen to shift sideways. Which way does the central maximum move (toward or away from the slit with the glass) and by how far?
For what slit-width-to-wavelength ratio does the first minimum of a single-slit diffraction pattern appear at (a) , (b) , and (c)
Scientists use laser range-finding to measure the distance to the moon with great accuracy. A brief laser pulse is fired at the moon, then the time interval is measured until the "echo" is seen by a telescope. A laser beam spreads out as it travels because it diffracts through a circular exit as it leaves the laser. In order for the reflected light to be bright enough to detect, the laser spot on the moon must be no more than in diameter. Staying within this diameter is accomplished by using a special large diameter laser. If , what is the minimum diameter of the circular opening from which the laser beam emerges? The earth-moon distance is
The wings of some beetles have closely spaced parallel lines of melanin, causing the wing to act as a reflection grating. Suppose sunlight shines straight onto a beetle wing. If the melanin lines on the wing are spaced apart, what is the first-order diffraction angle for green light ?
One day, after pulling down your window shade, you notice that sunlight is passing through a pinhole in the shade and making a small patch of light on the far wall. Having recently studied optics in your physics class, you're not too surprised to see that the patch of light seems to be a circular diffraction pattern. It appears that the central maximum is about across, and you estimate that the distance from the window shade to the wall is about . Estimate (a) the average wavelength of the sunlight (in ) and (b) the diameter of the pinhole (in ).
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