ConceptCheck 2-1: The speed of light is incredibly fast, which made it very difficult to measure its speed precisely before modern technology, except over enormous distances.
ConceptCheck 2-2: As Newton found when passing sunlight through a series of prisms, when one color is isolated from white light, there are no longer any other colors present in the remaining light. As a result, you cannot turn pure green into any other color by passing it through a plastic gel.
ConceptCheck 2-3: A more vigorous shaking of the pan would make more waves and make them crest higher, but the speed of waves across the water would stay the same, in much the same way that light can only travel so fast through outer space.
ConceptCheck 2-4: The width of your finger is about 1 cm, which falls in the range of the wavelength of microwaves (1 mm to 10 cm).
ConceptCheck 2-5: Because the relationship between wavelength and frequency is written as c = λ × f, wavelength and frequency are inversely related; as one increases the other decreases. Thus, the longest wavelengths have the lowest frequencies and the shortest wavelengths have the highest frequencies.
ConceptCheck 2-6: Infrared light is the most typical wavelength of light emitted by objects at temperatures common on Earth’s surface.
ConceptCheck 2-7: A star is hotter than our Sun if the dominant wavelength emitted is shorter than the light from our Sun.
ConceptCheck 2-8: The shorter the wavelength, the hotter the star, so the blue star will be at a higher temperature.
ConceptCheck 2-9: Photons with longer wavelengths will have lower energy than those with shorter wavelengths because the greater the wavelength, the lower the energy of a photon associated with that wavelength.
ConceptCheck 2-10: An absorption spectra results when the light from a hot, dense object passes through the cooler, transparent gas of our atmosphere.
ConceptCheck 2-11: When the distance between an object and a source is decreasing, the emissions lines will be shifted toward shorter wavelengths; alternatively, when the distance between an object and a source is decreasing, the emissions lines will be shifted toward longer wavelengths.
ConceptCheck 2-12: The diameter, because it is the width of the opening that determines how much light can be captured by the telescope.
ConceptCheck 2-13: The thin lens bends light less, so, according to Figure 2-21, it must focus light at a more distant location.
ConceptCheck 2-14: The larger the eyepiece focal length, the smaller the magnification.
ConceptCheck 2-15: Reflecting telescopes use mirrors that can be made to be lightweight rather than glass lenses, which are quite heavy and difficult to construct.
ConceptCheck 2-16: Adaptive optics actuators slightly deform the telescope’s mirror to match the apparent movement of a star due to distortions in Earth’s atmosphere. The actuators must deform the mirror more on nights when the stars appear more distorted due to a rapidly fluctuating atmosphere.
ConceptCheck 2-17: Given these three choices, astronomers would much prefer to have a new telescope in the microwave region because X-rays and ultraviolet wavelengths rarely pass through Earth’s atmosphere to the ground.
ConceptCheck 2-18: Orbiting space telescopes are placed far above most of Earth’s atmosphere, which blocks many wavelengths of light that astronomers want to see.
ConceptCheck 2-19: CCDs are able to detect 70% of the light that falls on them as compared to photographic film, which only captures 2% of the light, making CCDs far more efficient.
CalculationCheck 2-1: A popular radio station in Phoenix is 90.5 MHz. To calculate the wavelength of these radio waves, we rearrange the equation c = f ÷ λ to get λ = 3 × 108 m/s ÷ 90.5 × 106 Hz = 3.31 m.
CalculationCheck 2-2: Wien’s law can be rearranged to calculate the temperature of a star as T = 0.0029 K m ÷ (5800 K × 2) = 250 nm, which is ultraviolet.
CalculationCheck 2-3: F − σT4, so if temperature is 3 times greater, then the energy flux is 34, or 81 times greater than the flux from the Sun.
CalculationCheck 2-4: v = c × Δλ = 3 × 105 km/s × (486.3 nm − 486.2 nm) ÷ 486.2 nm = 61.7 km/s, and because it is moving toward longer wavelengths, the distance between the observer and the star must be increasing.