Why is a variable star so convenient for measuring distances to very remote objects?
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Certain types of variable stars, such as Cepheids and RR Lyrae stars, pulsate with a precise period that is easily determined by observing variations in the star's apparent magnitude. The period of a Cepheid is directly related to the absolute magnitude of the Cepheid and RR Lyrae stars have generally all the same absolute magnitude. When the apparent and absolute magnitudes of a star are known, its distance can be immediately calculated. Because Cepheids, in particular, are among the brightest stars known, they can be seen over large distances. Thus Cepheids are excellent for determining distances to remote objects.
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Photoelectric Effect: Monochromatic light is incident on a metal surface, and the ejected electrons give rise to a current in the circuit shown in the figure. The maximum kinetic energy of the ejected electrons is determined by applying a reverse ('stopping') potential, sufficient to reduce the current in the ammeter to zero. If the intensity of the incident light is increased, how will the required stopping potential change?
A. It will remain unchanged. B. It will increase. C. It will decrease.
When a vertically falling firecracker bursts, the vector sum of momentum fragments
A) in the horizontal direction cancels to zero. B) in the vertical direction equals the momentum of the firecracker before bursting. C) both of these D) neither of these
Explain how some stars form in binary systems
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A capacitor, initially charged, and an inductor form an LC circuit. When the electric current in the circuit is equal to zero how much energy is stored on each device?
A) Inductor: zero energy. Capacitor: zero energy B) Inductor: Half of the maximum energy. Capacitor: Half of the maximum energy C) Inductor: maximum energy. Capacitor: zero energy D) Inductor: zero energy. Capacitor: maximum energy E) Inductor: maximum energy. Capacitor: maximum energy