Just as in the case of r-c circuits, the steady state here is never actually reached: the exponential functions approach their limits asymptotically as t→[infinity] . however, it usually does not take very long for the value of i to get very close to its presumed limiting value. the next several questions illustrate this point. note that the quantity l/r has dimensions of time and is called the time constant (you may recall similar terminology applied to r-c circuits). the time constant is often denoted by τ . using τ , one can write the expressioni(t)=er(1−e−rt/l)asi(t)=e r(1−e−t/τ) .find the ratio of the current i(t) at time t=6τ to the maximum current imax=er .express your answer numerically, using three significant figures.

Ashielded metal arc-welding operation is accomplished in a work cell by a fitter and a welder. the fitter takes 5.5 min to load components into the welding fixture at the beginning of the work cycle, and 1.5 min to unload the completed weldment at the end of the cycle. the total ength of the weld seams 1200 mm, and the travel speed used by the welder averages 300 mm/min. every 600 mm of seam length, the welding stick must be changed, which takes 0.8 min. while the fitter is working, the welder is idle (resting): and while the welder is working the fitter is idle. (a) determine the average arc-on time as a fraction of the work cycle time. (b) how much improvement in arc-on time would result if the welder used flux-cored arc welding (manually operated), given that the spool of weld wire must be changed every 10 weldments, and it takes the welder 5.0 min to accomplish the change? (c) what are the production rates for these two cases (weldments completed per hour)? attach your work and solutions.