Calculate the threshold concentration of electron-hole pairs needed for lasing in gaas as a function of temperature. at room temperature (= 300k) for gaas: nc = 4.7 x 10" cm"; ny = 7 x 108 cm? ; and e, = 1.42 ev.

Three different objects, all with different masses, are initially at rest at the bottom of a set of steps. each step is of uniform height . the mass of each object is a multiple of the base mass : object 1 has mass 4..00m , object 2 has mass 1..96m , and object 3 has mass . when the objects are at the bottom of the steps, define the total gravitational potential energy of the three-object system to be zero. if the objects are then relocated as shown, what is the new total potential energy of the system? each answer requires the numerical coefficient to an algebraic expression. each algebraic expression is given using some combination of the variables , , and , where is the acceleration due to gravity. enter only the numerical coefficient. (example: if the answer is 1..23mgd , just enter 1.23)

Astronomers studying the planet of rhombus have detected sedimentary rock on its surface. one astronomer wonders if material in this sedimentary rock used to be in igneous rock deep in rhombus’s interior. can igneous rock become sedimentary rock? explain your answer.

Which sentences describe point source pollution? in this type of pollution, the source of the pollution is single and easily identifiable. when runoff water from the melting of snow mixes with debris, it creates pollution. the runoff water, mixed with pollutants, reaches large areas with disastrous effects. alternatively, when a wastewater treatment plant releases harmful chemicals into a stream, the chemicals pollute the stream water because they are not treated for safety.