# Homework Help: Capacitor charge time

1. May 23, 2012

### Femme_physics

1. The problem statement, all variables and given/known data

The following is a circuit to activate D.C. motor. The circuit contains a capacitor that charges and discharges, and a circuit to activate/disconnect the D.C. motor (which does not appear in the drawing). When pressing P1, the capacitor C is charged, and when it reaches 30 volts the motor is activated. When pressing P2 the capacitor discharges, and when it reaches 10 Volts the motor stops running.

COMMENT: when the motor is turned on or off, the button P1 and P2 are released immediately correspondingly, so not to let the capacitor keep on charging or discharging beyond needed (over 30 volts or below 10 volts)

http://img208.imageshack.us/img208/927/ppppv.jpg [Broken]

Question: The capacitor is discharged. Calculate the the pressing time needed (t1) to activate the motor for the first time.

2. Relevant equations

In the attempt

3. The attempt at a solution

I think I'm handling this correctly...

http://img94.imageshack.us/img94/6931/chargefix.jpg [Broken]

http://img62.imageshack.us/img62/6247/charge2y.jpg [Broken]

Last edited by a moderator: May 6, 2017
2. May 23, 2012

### I like Serena

Perfect!
I give it my stamp of approval. :)

(Flowers?)

3. May 23, 2012

### Femme_physics

Oh yea, that ;)

http://img269.imageshack.us/img269/3197/300mw.jpg [Broken]

Overkill? Just trying to look sexy :P

The flower is fake but this is only between us

There is another clause to that question but I'll post back soon^^

Last edited by a moderator: May 6, 2017
4. May 23, 2012

### I like Serena

There's no such thing as overkill! I like it!!

5. May 24, 2012

### Femme_physics

Hehe...thanks... I got the rest of it verified by a friend so I'll skip posting the other clauses. Much appreciated ILS :)