Astraight, cylindrical wire lying along the x axis has a length l and a diameter d. it is made of a material described by ohm's law with a resistivity rho. assume potentialv is maintained at the left end of the wire at x = 0. also assume the potential is zero at x = l. in terms of l, d, v, rho, and physical constants, derive expressions for the following. (use the following as necessary: l, d, v, rho, and π.)

(a) the electric field in the wire

magnitude
direction +i -i +j -j +k -k

(b) the resistance of the wire
r =

(c) the electric current in the wire

magnitude
direction +i -i +j -j +k -k

(d) the current density in the wire

magnitude
direction +i -i +j -j +k -k

Sawyer is studying diffraction. he draws a diagram of a plane wave to show how light waves travel. which best describes sawyer’s error? the wave fronts should be perpendicular to the direction in which the waves move. the arrow showing the direction of movement of the waves should be pointing to the left. the arrow showing the direction of movement of the waves should be pointing downward. the wave fronts should be both parallel and perpendicular to the direction in which the waves move.

Some material consisting of a collection of microscopic objects is kept at a high temperature. a photon detector capable of detecting photon energies from infrared through ultraviolet observes photons emitted with energies of 0.3 ev, 0.5 ev, 0.8 ev, 2.0ev, 2.5ev, and 2.8ev. these are the only photon energies observed. (a) draw and label a possible energy-level diagram for one of the microscopic objects, which has four bound states. on the diagram, indicate the transitions corresponding to the emitted photons. explain briefly. (b) would a spring–mass model be a good model for these microscopic objects? why or why not? (c) the material is now cooled down to a very low temperature, and the photon detector stops detecting photon emissions. next, a beam of light with a continuous range of energies from infrared through ultraviolet shines on the material, and the photon detector observes the beam of light after it passes through the material. what photon energies in this beam of light are observed to be significantly reduced in intensity (“dark absorption lines”)? explain briefly.

What determines the amount of inertia an object has