The coolest white-dwarf: Surveys have been carried out to identify isolated white-dwarfs throughout the galaxy and its globular clusters
They have been found to span a range of temperatures, with a sharp lower limit of about 3000 K (i.e. many have been found at all temperatures from 10s of thousands of Kelvin down to 3000K, but none cooler). What does this observation reveal about the age of our galaxy?
The galaxy has a finite age, when enough gas must have become present to generate stars which could go on to become white dwarfs. (This observation is one of the supporting pieces of evidence for the approximately 13 billion year age of the universe — the coolest observed white dwarfs are about 10 billion years old)
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What is the electric potential at a given point in space, in terms of the work done to bring a small positive test charge from a reference location where the potential is taken to be zero?
a. The work done to bring the test charge to the point, divided by its charge, expressed in volts. b. Charge per amount of work, expressed in volts. c. The same as the electric potential energy. d. The electric force experienced by the charge divided by charge, or newtons per coulomb. e. The electric force experienced by the charge, calculated as charge divided by electric potential energy.
As sediment travels in a downstream river, it changes by getting
A) coarser. B) finer. C) more poorly sorted. D) more angular.
A marble has a diameter of 2 cm. At what distance would the marble have an angular diameter of 1 arc second
a. 4.1 cm b. 4.1 miles c. 4.1 m d. 4.1 ft e. 4.1 km
Graphical Interpretation of Work: A force acts on an object, causing it to move parallel to the force. The graph in the figure shows this force as a function of the position of the object. How much work does the force do as the object moves from 0 m to 4 m?
A. 20 J B. 30 J C. 0 J D. 40 J E. 70 J