A capacitor charges from a cell through a resistance. The time constan

1.	A capacitor charges from a cell through a resistance. The time constant is τ. In what time will the capacitor collect 10% of its final charge? (a) τ In (0.1) (b) τ In (0.9) (c) τ In (10/9) (d) τ In (11/10)
Answer» Correct Answer is: (c) τ In (10/9) Q = Q₀(1 - e ^-t/τ ) = 0.1Q₀ or e ^-t/τ = 0.9 or e^t/τ = 10/9.

A capacitor charges from a cell through a resistance. The time constant is τ. In what time will the capacitor collect 10% of its final charge? (a) τ In (0.1) (b) τ In (0.9) (c) τ In (10/9) (d) τ In (11/10)

Answer»

Correct Answer is: (c) τ In (10/9)

Q = Q₀(1 - e ^-t/τ ) = 0.1Q₀

or e ^-t/τ = 0.9 or e^t/τ = 10/9.