# What is the Formula -RC series circuit impedance & current

#### ironasona

Joined Nov 12, 2020
53
Hello am kind of new to all the electronics .So I was told to measure the voltage across the capacitor and the current of frequencies between 1khz and 10khz

so i was wondering what is the formula to finding them

100ohm resistor
0.01uF capacitor

thank you

#### ericgibbs

Joined Jan 29, 2010
18,072
hi iron,
A resistor is a passive component, its resistance should be the same at all frequencies, so use Ohms Law.

What is the voltage amplitude of the 1kHz to 10kHz signal and is sinusoidal.?

E

#### ironasona

Joined Nov 12, 2020
53
hi iron,
A resistor is a passive component, its resistance should be the same at all frequencies, so use Ohms Law.

What is the voltage amplitude of the 1kHz to 10kHz signal and is sinusoidal.?

E
i set it at 10V

#### ericgibbs

Joined Jan 29, 2010
18,072
hi,
Ohms Law equation, Amps = Volts/Resistance

So for 10V that's 10v/100ohms = ...............................Amps?

E

#### ironasona

Joined Nov 12, 2020
53
hi,
Ohms Law equation, Amps = Volts/Resistance

So for 10V that's 10v/100ohms = ...............................Amps?

E
so i just do 10v/100ohms = 10Amps ? and thats the current and the voltage ?

#### ericgibbs

Joined Jan 29, 2010
18,072
10v/100ohms = 10Amps ?

hi,
10/100 is not 10

E

#### ironasona

Joined Nov 12, 2020
53
10v/100ohms = 10Amps ?

hi,
10/100 is not 10

E
ye sorry 0.1 , but is that all is that the current and the voltage across the capacitor ?

#### ericgibbs

Joined Jan 29, 2010
18,072
hi,
That's better, we are doing the resistor first as it's the easiest.

So, 10v/100ohm = 0.1Amp as you say.

The capacitor is very different from a resistor as its impedance [ resistance] changes with frequency

You still have 10v across the capacitor BUT, the resistance is now Z= 1/ (2 *pi *freq * capacitance}

E

#### ironasona

Joined Nov 12, 2020
53
ok so it would be 1(2*pie*freq*capacitance) but , what do i put in the freq, is it HZ/KHz and in the capacitance do i put uF/F or etc, or it doesn't matter? and then it would be 1(2*pie*1000*0.01)=0.01591? . 0.01uF and 1000Hz

#### ericgibbs

Joined Jan 29, 2010
18,072
hi,
If your tutor has asked you for all the current at ALL frequencies between 1kHz and 10kHz, you cannot be expected to give 10,000 answers.!

So choose 1kHz and say 10kHz

That would be Impedance[Resistance] = 1/( 2 * pi * F * C)

Z= 1/( 2 * 3.142 * 1000 * 0.01*10^-6)

Can you work out the Zohms value .???

E

#### ironasona

Joined Nov 12, 2020
53
hi,
If your tutor has asked you for all the current at ALL frequencies between 1kHz and 10kHz, you cannot be expected to give 10,000 answers.!

So choose 1kHz and say 10kHz

That would be Impedance[Resistance] = 1/( 2 * pi * F * C)

Z= 1/( 2 * 6.28 * 1000 * 0.01*10^-6)

Can you work out the Zohms value .???

E
is it 7961.78343 ?

#### ericgibbs

Joined Jan 29, 2010
18,072
hi
Note I corrected the 6.28 to 3.142, I have got so used to using 2pi =6.28!!
So your answer should be doubled. Z= 1/( 2 * 3.142 * 1000 * 0.01*10^-6) =15,923 ohms

So using that answer what will the current be for 10volts.??
E

#### ironasona

Joined Nov 12, 2020
53
hi
Note I corrected the 6.28 to 3.142, I have got so used to using 2pi =6.28!!
So your answer should be doubled. Z= 1/( 2 * 3.142 * 1000 * 0.01*10^-6) =15,923 ohms

So using that answer what will the current be for 10volts.??
E
sorry you kind lost me there .The current for 10v will be 15,923ohms ? , am kind lost sorry

#### ericgibbs

Joined Jan 29, 2010
18,072
hi,
OK,
Use Ohms Law.

Current in Amps = 10V/15923ohms = ____________________.?

E
BTW: always use a letter to indicate the units you are using...eg: 15923 ohms

#### ironasona

Joined Nov 12, 2020
53
hi,
OK,
Use Ohms Law.

Current in Amps = 10V/15923ohms = ____________________.?

E
BTW: always use a letter to indicate the units you are using...eg: 15923 ohms
so the current would be 6.28V ?and thats all ?

#### ericgibbs

Joined Jan 29, 2010
18,072
hi,
How can the current be 6.28V
Try;
Current in Amps = 10V/15923ohms =......???.................. Amps.

#### ericgibbs

Joined Jan 29, 2010
18,072
hi irona,
What level are you at, with your electronic studies.?
E

#### ironasona

Joined Nov 12, 2020
53
hi,
How can the current be 6.28V
Try;
Current in Amps = 10V/15923ohms =......???.................. Amps.
Sorry i think am just being dum is it 0.00062802235Amps ?

#### ericgibbs

Joined Jan 29, 2010
18,072
hi,
The number is correct, but why have you put V instead of A ident.??
0.00062802235V ?
Remember you are measuring current in amps.

0.00062802235A

Now do the 10kHz question, post your calculations.
E

OT: We Yorksire lads must work together... #### ironasona

Joined Nov 12, 2020
53
hi,
The number is correct, but why have you put V instead of A ident.??
0.00062802235V ?
Remember you are measuring current in amps.

0.00062802235A

Now do the 10kHz question, post your calculations.
E

OT: We Yorksire lads must work together... Thank you so much ,you're an absolute legend . 