The approximate main-sequence lifetime of a star of spectral type O is
A) 3 million years.
B) 10,000 years.
C) 300 million years.
D) 10 billion years.
A) 3 million years.
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Diffraction Gratings: A diffraction grating is to be used to find the wavelength of the emission spectrum of a gas. The grating spacing is not known, but light of a known wavelength of 632.8 nm is deflected by 43.2° in the second order by this grating. Light of the wavelength to be measured is deflected by 34.9° in the second order. What is the wavelength of the light that is to be measured?
Fill in the blank(s) with the appropriate word(s).
Optics of the Eye: A person's eye lens is 2.8 cm from the retina, and his near point is at 25 cm. What must be the focal length of his eye lens so that an object at the far point of the eye will focus on the retina?
A. -2.8 cm B. 2.8 cm C. -2.4 cm D. 2.4 cm E. 2.2 cm
How is the magnification, mo, of the objective lens in a microscope related to the focal length, fo, of the lens?
A. Amo= -1/fo B. mo= -fo/L C. mo= -L/fo D. mo= L - fo
Studying a spectrum from a star can tell us a lot. All of the following statements are true except one. Which statement is not true?
A) The total amount of light in the spectrum tells us the star's radius. B) The peak of the star's thermal emission tells us its temperature: hotter stars peak at shorter (bluer) wavelengths. C) We can identify chemical elements present in the star by recognizing patterns of spectral lines that correspond to particular chemicals. D) Shifts in the wavelengths of spectral lines compared to the wavelengths of those same lines measured in a laboratory on Earth can tell us the star's speed toward or away from us.