Question

The magnetic field due to the current in a long, straight wire is 8.0 mu T at a distance of 4.0 cm from the center of the wire. What is the current is the wire? 0.20 A 0.40 A 0.80 A 1.6 A 3.2 A Draw a circuit consisting of a battery connected to two resistors, R_1 and R_2, in series with each other and a capacitor C connected across the resistors. Most extra-cellular environments contain a high concentration of sodium ions (Na^+). Consider a cell membrane that is permeable to potassium (K^+) and is equilibrium - The diffusion of K^+ has left the inside of the cell slightly negatively charged and the outside slightly positively charged. Suppose that the cell membrane now opens some sodium channels. What happen? There is no flow across the membrane; The outside of the cell is positively charged, driving the sodium ions farther away from the cell There is no flow across the membrane; The cell is in equilibrium, and so the electric repulsion of the Na exactly counters the effects of diffusion. The cell becomes positively charged; both diffusion and the electric attraction to the cell drive Na^+ into the cell. The cell becomes positively charged; diffusion is reversed and K^+ are driven back into the cell.

Answer 1

$magnetic field = \tfrac{\mu I }{2\pi r}$

8*10^-6 = 4* $\pi$ *I/2 $\pi$ *4*10^-2

I = 1.6 A

so D ans