Final answer:
The electric current i in the circuit for t=7.0 ms is calculated by plugging the time in seconds (after converting from milliseconds) into the given exponential formula and performing the exponential function calculation to find the current at that specific time.
Step-by-step explanation:
The student has asked to evaluate the current i in a circuit at a given time t using the formula i=8.6(1-e⁻⁰.³⁹ᵗ), where t is in seconds and i is in milliamperes (mA). To calculate the electric current for t=7.0 ms (milliseconds), one must remember to convert milliseconds to seconds by dividing by 1000, as 1 ms = 0.001 s. Plugging the value of t=0.007 s (7.0 ms) into the formula, we get:
i=8.6(1-e⁻⁰.³⁹(0.007))
Carrying out the calculation yields a specific current value in mA, which gives the current in the circuit at that instant.