When a star moves off the main sequence and becomes a red giant it is brighter because
A. the size of the star increases.
B. the star's mass increases.
C. the star moves closer to Earth.
D. the surface temperature increases.
Answer: A
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The diagram shown represents a portion of a wire in a circuit. A current is flowing in the wire in the direction shown. Under the convention that it is positive charge that flows the electric field points in the direction of the current. How can the electric field change direction where the wire bends?
A. There is an excess of negative charge in the center of the wire. B. There is an excess of positive charge at the bottom end of the wire. C. There is an excess of negative charge at the right end of the upper portion of the wire. D. There is an accumulation of positive charge on the surface, particularly at the bend, such that the sum of electric fields gives the new electric field. E. There is an accumulation of electrical potential as the current traverses the wire: The higher potential in the lower half is the source of the field.
A solid state pulsed laser has an energy of 400 mJ per pulse. If its wavelength is 1.06 × 10^-6 m, how many photons are in each pulse?
a. 2 × 10^25 b. 2 × 10^21 c. 3 × 10^18 d. 6 × 10^38 e. 2 × 10^18
X-rays are produced using a potential difference of V. The spectrum of wavelengths is found to contain
A. a single wavelength. B. all wavelengths from zero up to a maximum. C. all wavelengths from a minimum to a maximum. D. only discrete wavelengths.
Which of the following statements best describes one astronomical unit (AU)?
A) It is the distance from Earth to the Moon. B) It is equal to the average distance of the Sun from Earth. C) It is the distance that light travels in a vacuum in one year. D) It is the average distance between two stars in the Milky Way.