4.38 a diode operates in a series circuit with a resistance r and a dc source v. a designer, considering using a constant-voltage model, is uncertain whether to use 0.7 v or 0.6 v for vd. for what value of v is the difference in the calculated values of current only 1%? for v = 3 v and r = 1 k! , what two current estimates would result from the use of the two values of vd? what is their percentage difference?

As you are trying to move a heavy box of mass m, you realize that it is too heavy for you to lift by yourself. there is no one around to , so you attach an ideal pulley to the box and a massless rope to the ceiling, which you wrap around the pulley. you pull up on the rope to lift the box. use g for the magnitude of the acceleration due to gravity and neglect friction forces. once you have pulled hard enough to start the box moving upward, what is the magnitude f of the upward force you must apply to the rope to start raising the box with constant velocity? express the magnitude of the force in terms of m, the mass of the box.

The reason a penny thrown straight up inside a bus will come back to your hand is that you,the bus,the air inside the bus, and the penny are all moving at the same velocity. true or false

One kind of e-book display consists of millions of very small spheres that float in a thin fluid layer between two conducting transparent plates. each sphere is black on one side and white on the other, and possesses an electric dipole moment directed from the white side to the black. when an electric field is applied between the plates, the spheres rotate so that their dipole moment lines up with the field. depending on the fields direction, either the black or the white sides of th espheres can be made visible.the dipole moment of the spheres can be modeled as two opposite charges of magnitude 3.5 x 10^-15 c, separated by a distancce of 100 micrometers (um). what is the maximum possible torque on a sphere if the electric field between the transparent plates is 4.0 x 10^5 n/c