RC circuits?

Question

the duration of a photographic flash is related to an RC time constant, which is 0.100 us for a certain camera. If the resistance of the flash lamp is 0.0400 ohm during discharge, what is the size of the capacitor supplying its energy? What is the time constant for charging the capacitor, if the charging resistance is 800 k ohm?

Answer 1

If RC = 0.100us, and R = 0.0400ohm, then C = 2.5uF

For charging, if C = 2.5uF, R = 800kOhm, then RC = 2s

Answer 2

RC means resistance times capacitance. Ohms times Farads. and the answer is in seconds. RC is called the "time constant".