physics

A resistor 3 Mega ohms and a capacitor of 350 mirco F are connected in series to a 50V power supply. Calculate the time constant.

Do I need to solve for an actual number? I'm confused

1. 👍 0
2. 👎 0
3. 👁 60
1. The time constant of an RC circuit is the time it takes the capacitor to charge or discharge 63.2% (= 1 - 1/e) of the way when the circuit is open or closed.

The time constant equals RC.

In your case, that is 1050 seconds or 17.5 minutes. You don't need to know the voltage.

1. 👍 0
2. 👎 0
posted by drwls
2. Thanks so much..okay for part b it saysto find the current at a time when the charge on the capacitor has aquired 90% of its maximum value.

Do I use the same equation or time constant for this?

1. 👍 0
2. 👎 0
posted by susan
3. The charge on the capacitor after closing the circuit is
Q = C V [1 - e^(-t/RC)]
Note the appearance of the RC "time constant" in this equation. I showwed earlier that RC = 1050 seconds
The maximum value of the charge (which occurs when t approaches infinity)is
Qmax = CV

When Q = 0.90*CV,
[1 - e^(-t/RC)] = 0.9
e^(-t/RC) = 0.1
t/RC = 2.3026
t = 2418 seconds = 40.3 minutes

1. 👍 0
2. 👎 0
posted by drwls

Similar Questions

1. Physics

A 67.6 ohms resistor is connected in parallel with a 103.8 ohms resistor. This parallel group is connected in series with a 20.8 ohms resistor. The total combination is connected across a 18.2-V battery. Find a) the current and b)

asked by Ellie on May 18, 2016
2. CIRCUITS

two resistors of 25 ohms and 5 ohms respectively are connected in series to a 240V supply calculate the value of a third resistor to be connected in parallel with 25 ohms resistor so that the power dissipated shall be tripled

asked by Kirchhoffs on September 25, 2017
3. physics

A 15.0 Ohms resistor is connected in series to a 120V generator and two 10.0 Ohms resistors that are connected in parallel to each other. -What is the total resistance of the load? -What is the magnitude of the circuit current?

asked by Rony on February 17, 2010
4. physics

a 2 uF capacitor is connected in series with a 1.2 M ohms resistor and a 5 v battery for a long time. What is the current in the resistor 1s after disconnecting the battery?

asked by JM on November 23, 2011
5. science

A 10 ohms, 8 ohms, and 5 ohms resistor connected in series to a Volts source. Find the current in each resistor.

asked by Anonymous on January 14, 2016
6. physics

A 350-ohm resistor is connected in series with a 270-ohm resistor. What is their equivalent resistance in ohms?

asked by elisabeth on November 2, 2011
7. Physics

A)Two identical resistors are connected in parallel across a 30-V battery, which supplies them with a total power of 7.0 W. While the battery is still connected, one of the resistors is heated so that its resistance doubles. The

asked by Kristi on October 24, 2011
8. Physics

A)Two identical resistors are connected in parallel across a 30-V battery, which supplies them with a total power of 7.0 W. While the battery is still connected, one of the resistors is heated so that its resistance doubles. The

asked by Kristi on October 22, 2011
9. Hvac

3 resistors of 5 ohms,15 ohms, and 30 ohms are connected in series and placed across a 50 volt batt. Find the voltage drops acroos each resistor . And find the current through each resistor

asked by Dave on July 18, 2013
10. College Physics

Two 9.1 ohms resistors are connected in parallel, as are two 5.9 ohms resistors. These two combinations are then connected in series in a circuit with a 20 V battery. What is the current in each resistor? I9.1, I5.9 = A What is

asked by Lanise on February 12, 2010

More Similar Questions