# B How many electrons on a Capacitor calculation

1. May 16, 2016

### ENE

Hello,
How to find number of electronics in capacitor?
as 1 coulomb and 1 Amp has 6.25x10^18
on what they depend?
Is this correct..?
Q=C*V
C=47uF and V=12V
Q=47*10^-6*12=5.64*10^-4 Coulmb?????

2. May 16, 2016

### Drakkith

Staff Emeritus
The number of electrons in a capacitor is given by Q=CV, which you've calculated correctly.

3. May 16, 2016

### ENE

Thanks.

I don't understand this graph
How the capacitor will charge with series Resistance?

4. May 17, 2016

### Drakkith

Staff Emeritus
5. May 17, 2016

### ENE

Hello,
I got
a. The rate of charging is typically described in terms of a time constant RC.
b. The electrical transient phenomena in capacitors and inductors are exponential processes

voltage across the capacitor
how we get exponential here?

6. May 18, 2016

### fizzle

The voltage on a capacitor is Vc = Q / C.

Note: you copied images from two different circuit explanations and that's causing confusion. The "Vb" in the first image is "Vs" in the second image.

7. May 19, 2016

### ENE

i have to learn this equation?

8. May 19, 2016

### Vanadium 50

Staff Emeritus
Oh, the horror! The horror!

Yes, you have to learn it.

9. May 19, 2016

### ENE

in electrical engineering how man equation are there?

10. May 19, 2016

### Staff: Mentor

We solve the differential equation for the circuit. See for example

http://web.mit.edu/molly/Public/circuits-b.pdf

and scroll down to page W6-6. This uses Q as the variable, not V, but you can change variables using Q = CV if you prefer.

11. May 19, 2016

### ENE

Hello,
Why The sum of the voltage drops∆Vi , across any circuit elements that form a closed circuit is zero.??

12. May 19, 2016

### ProfuselyQuarky

ENE, that's an awfully basic equation, you needn't worry

13. May 19, 2016

### Drakkith

Staff Emeritus
The answer to this is kind of in-depth and I don't feel you're ready for it at the moment.

14. May 19, 2016

### nasu

The static electric field is a conservative field. So the work done on a closed path is zero.
Do you understand the relationship between work and potential difference?

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