A hole current of 10-4 A/cm2 is injected into the side (x = 0) of a long N-silicon bar. Assuming that the hole flows only by diffusion, and that at very large values of x, the distribution of excess holes decays to zero. Determine, at T = 300 K:

a) The steady-state excess hole density at x = 0.
b) Repeat part (a) at x = 100 μm. Given μp = 400 cm2/V-s, μn = 1600 cm2/V-s, T = 300 K, and the lifetime of hole is 25 μs.

Asolid cylinder is concentric with a straight pipe. the cylinder is 0.5 m long and has an outside diameter of 8 cm. the pipe has an inside diameter of 8.5 cm. the annulus between the cylinder ad the pipe contains stationary oil. the oil has a specific gravity of 0.92 and a kinematic viscosity of 5.57 x 10-4 m2/s. most nearly, what is the force needed to move the cylinder along the pipe at a constant velocity of 1 m/s?