In star clusters, the ____ stars are giant stars fusing helium in their cores and then in their shells
a. turnoff point
b. main sequence
c. turnon point
d. hydrogen flash
e. horizontal branch
E
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A 1.0-mm diameter extension cord is made of metal having a resistivity of 1.68 × 10-8 ? ? m. When it carries a current of 15 A, what is the potential difference between two points in the cord that are 100 m apart?
A) 12 V B) 23 V C) 32 V D) 41 V
Why is it difficult to observe an exoplanet directly through a telescope?
A. It is hard to see exoplanets against the blackness of space. B. Exoplanets are small compared to their parent star, so they reflect only a small portion of the star's light. C. Exoplanets tend to be far away from their parent stars, making it hard to get both the star and the exoplanet in the telescope's field of view. D. Exoplanet atmospheres absorb too much light
When a wheel is rolling without slipping, the magnitude of its velocity relative to the ground is greatest at
a. the point in contact with the ground. b. the point at the center of the wheel. c. the point at the top of the wheel opposite to the point in contact with the ground. d. the point farthest forward from the center of mass of the wheel. e. the point farthest behind the center of mass of the wheel.
What is the wavelength of the photon emitted when an electron in a hydrogen atom which is in the initial state n = 8 jumps to the final state n = 2?
(c = 3.00 × 108 m/s, h = 6.626 × 10-34 J ? s, 1 eV = 1.60 × 10-19 J) A) 486 nm B) 205 nm C) 104 nm D) 610 nm E) 389 nm