RC Circuit find capacitor charge

[matt72lsu]

Homework Statement

The capacitor in an RC circuit (R = 130 \Omega, C = 40uF) is initially uncharged.
1) Find the charge on the capacitor in the circuit one time constant (tau = RC) after the circuit is connected to a 9.0- V battery.
2) Find the current in the circuit one time constant (\tau = RC) after the circuit is connected to a 9.0-V battery.

Homework Equations

R = V/I
Q = qo[1-e^-t(RC)] ?

The Attempt at a Solution

Im actually not sure I even have the correct equations and I'm not sure what to use for qo

 

[ehild]

Homework Statement

The capacitor in an RC circuit (R = 130 \Omega, C = 40uF) is initially uncharged.

Homework Equations

R = V/I
Q = qo[1-e^-t(RC)] ? not correct

The Attempt at a Solution

Im actually not sure I even have the correct equations and I'm not sure what to use for qo

Q=qo[1-e^(-t/(RC))]

ehild

 

[Lok]

R = V/I
Q = qo[1-e^-t(RC)] ?

Im actually not sure I even have the correct equations and I'm not sure what to use for qo

Qo=C*V

 

[matt72lsu]

I'm so confused

 

[rl.bhat]

In the problem C and V is given. When the capacity is fully charged, the maximum charge Qo = C*V. Find this one.
In the relevant equation, put t = RC and find Q.

 

[matt72lsu]

i got the first part but i got the second part wrong. i did V/R = 6.9e-2. then i multiplied that by 1-e^-1 and got 4.4e-2 then multiplied that by 1000 to go from A to mA and got 44. where did i go wrong?

 

[Lok]

There is a similar formula to the Q=qo[1-e^(-t/(RC))] for I(ntensity). It is a must have.

 

[matt72lsu]

yeah I used that and substituted qo for V/R and worked it out the same way i did the first one

 

[rl.bhat]

The current I = dQ/dt = (qo/RC)[1-e^(-t/(RC))]
Now find the current.

 

[matt72lsu]

i can't wrap my mind around this !

 

[rl.bhat]

i can't wrap my mind around this !

The current I = dQ/dt = (qo/RC)[e^(-t/(RC))]
Now find the current.