The first known telescopes, used around 1600, consisted of a lens and an eyepiece. today, telescopes are often computer controlled and consist of a complicated array of sophisticated lenses. which statement correctly describes how telescopes have changed over time? a. the telescopes of the 1600s were used until the year 2000, when a more sophisticated telescope was built. b. the telescopes of the 1600s were gradually improved upon over time, resulting in the telescopes that are available today. c. the telescopes of the 1600s were used until the year 1900, when a more sophisticated telescope was built that was used until the year 2000. d. the telescopes of the 1600s were abandoned after about 50 years, and the technology was completely replaced.

Under conditions for which the same room temperature is maintained by a heating or cooling system, it is not uncommon for a person to feel chilled in the winter but comfortable in the summer. provide a plausible explanation for this situation (with supporting calculations) by considering a room whose air temperature is maintained at 20â°c throughout the year, while the walls of the room are nominally at 27â°c and 14â°c in the summer and winter, respectively. the exposed surface of a person in the room may be assumed to be at a temperature of 32â°c throughout the year and to have an emissivity of 0.90. the coefficient associated with heat transfer by natural convection between the person and the room air is approximately 2 w/m2 â‹…â‹… k. what is the ratio of the thermal resistance due to convection to the thermal resistance due to radiation in the summer? what is the ratio of thermal resistances in the winter

The movement of electrons between atoms is called an

Cyclotrons are widely used in nuclear medicine for producing short-lived radioactive isotopes. these cyclotrons typically accelerate h- (the hydride ion, which has one proton and two electrons) to an energy of 5 mev to 20 mev. this ion has a mass very close to that of a proton because the electron mass is negligible—about 1 2000 of the proton’s mass. a typical magnetic field in such cyclotrons is 1.9 t. (a) what is the speed of a 5.0-mev h-? (b) if the h- has energy 5.0 mev and b = 1.9 t, what is the radius of this ion’s circular orbit?