Aphysics professor wants to show an interference pattern made by shining a laser on two thin slits that are separated by a distance of o.075 mm. the professor knows that she cannot get the interference pattern large enough to show to her class by just placing the slits 7 m away from the wall, so she asks her colleagues for advice. one colleague seems to remember that another professor, who retired several years ago, used to do a similar demonstration and sends the first professor to the demo room to see what she can find. the professor finds a piece of equipment that seems to be what she is looking for. a translucent screen is connected to a metal bracket that can hold two lenses. one lens is located about 10 cm from the screen and the second lens could be placed anywhere from 5 cm to 15 cm in front of the first lens (farther away from the screen) on an adjustable arm. the professor figures that an interference pattern could be made on one side of the translucent screen and the lenses could form a system that allows the final image to be projected on a distance wall or screen. a quick measurement of the first lens indicates that it has a focal length of -17 cm assume that the physics professor has a variety of lasers available to use for this demonstration. the apparatus will be placed on a table 7 m away from the wall upon which she wishes to display the projected interference pattern. (the laser is separate from the screen/lens apparatus but it will sit on the same table.) the professor decides that an interference pattern with a distance of about 75 cm between the two m- 2 bright fringes will be easy enough for her entire class to see (a) determine the focal length of the second lens that could make the demonstration work. (b) the professor cannot find a lens with that focal length that fits in the bracket on the ap- paratus the one that the retired professor used must have broken years ago! she decides to call in a favor to a friend from graduate school that now works at an optics fabrication shop. what should her "order" be? (consider the lens maker's equation) c) how many times larger is the projected interference pattern than one that could be made with just the slits alone? assume that the intensity of the image is enough for it to be seen easily note: there are many possible answers to this problem depending on choices that you? ve made be sure to clearty state any assumption that you?

  sequence  is a continuous and distinctive band of  stars  that appears on plots of stellar  color  versus  brightness. these color-magnitude plots are known as  hertzsprung–russell diagramsafter their co-developers,  ejnar hertzsprungand  henry norris russell. stars on this band are known as  main-sequence stars  or  dwarf stars. these are the most numerous true stars in the universe, and include the earth's  sun.after condensation and ignition of a star, it generates  thermal energy  in its dense core region through  nuclear fusion  of  hydrogen  into  helium. during this stage of the star's lifetime, it is located on the main sequence at a position determined primarily by its mass, but also based upon its chemical composition and age. the cores of main-sequence stars are in  hydrostatic equilibrium, where outward thermal pressure from the hot core is balanced by the inward pressure of  gravitational collapse  from the overlying layers. the strong dependence of the rate of energy generation on temperature and pressure to sustain this balance. energy generated at the core makes its way to the surface and is radiated away at the  photosphere. the energy is carried by either  radiation  or  convection, with the latter occurring in regions with steeper temperature gradients, higher opacity or both.the main sequence is sometimes divided into upper and lower parts, based on the dominant process that a star uses to generate energy. stars below about 1.5 times the  mass of the sun  (1.5  m☉) primarily fuse hydrogen atoms together in a series of stages to form helium, a sequence called the  proton–proton chain. above this mass, in the upper main sequence, the nuclear fusion process mainly uses atoms of  carbon,  nitrogen  and  oxygen  as intermediaries in the  cno cycle  that produces helium from hydrogen atoms. main-sequence stars with more than two solar masses undergo convection in their core regions, which acts to stir up the newly created helium and maintain the proportion of fuel needed for fusion to occur. below this mass, stars have cores that are entirely radiative with convective zones near the surface. with decreasing stellar mass, the proportion of the star forming a convective envelope steadily increases. main-sequence stars below 0.4  m☉undergo convection throughout their mass. when core convection does not occur, a helium-rich core develops surrounded by an outer layer of hydrogen.in general, the more massive a star is, the shorter its lifespan on the main sequence. after the hydrogen fuel at the core has been consumed, the star  evolves  away from the main sequence on the hr diagram, into a  supergiant,  red giant, or directly to a  white dwarf.

  concave means having an outline or surface that curves inward like the interior of a circle or sphere. so the mirror curves inward.

Answer(b) 60 miles per hour;