A 40- $\mu$ F Capacitor Is Charged Through a 30-K $\Omega$ Resistor the Time Needed to Charge the Capacitor to 70

Multiple Choice

A 40- $\mu$ F capacitor is charged through a 30-k $\Omega$ resistor. The time needed to charge the capacitor to 70% of its full charge is

A) 8.4 s.
B) 0.84 s.
C) 2.1 min.
D) 0.14 s.
E) 1.4 s.