# Physics

posted by .

The circuit below consists of three identical resistors each with resistance R=7 Ohm, two identical batteries with emfs E=9 V, and a capacitor with capacitance C=651 μF. The capacitor is initially uncharged at t = 0.

(a) After a very very long time, t≫RC, what is the current i1 (in A)?
i1=

(b) After a very very long time, t≫RC, what are the currents i2 and i3 (in A)?

i2=

i3=

(c) After a very very long time, t≫RC, what is the magnitude of the voltage (in V ) across the capacitor ?
VC=

(d) Assuming that the capacitor starts uncharged, how long will it take (in seconds) for the voltage across the capacitor to reach 3/4 of its maximum value?
t=

• Physics -

Are the batteries and resistors in parallel or series?
It makes a difference.

There is no "circuit below"

• Physics -

i would like to post the photo of it but i have no clue how

• Physics -

what find t?
it is correct: t = -ln(0.25)*RC ? and what shuld be R?

• Physics -

maybe R=Req? i'm not sure

• Physics -

t=-ln(0.25)*RC correct

• Physics -

i1 = 0
i2 = i3 = U/(2*R)
U on Cap = (3/4)*(2U)

give pliz form on 1d

• Physics -

BoobleGum, what is the value for U please?

• Physics -

I have both batteries on 5 volts, and voltage on the condenser of 7.5 volts

• Physics -

Sorry Booblegum, what is value U? I don't get it

• Physics -

Did somebody figure out problem after the first question please?

I don't seem to get it with above formula.

• Physics -

What value is U by the way?

• Physics -

Flu, U is the voltage of the battery

• Physics -

Many thanks Phy!
Could you help with this please. This was provide by hmmmm and anonymous but only c) works for me.

Did you get this:
formula for question 2
a)B=meu_0*N*I/l
b)L=meu_0*N^2*A//l
c)I=V/R
d)U=1/2(LI^2)

• Physics -

Are these the formulas for 2nd problem?

• Physics -

Yeah, only c) worked for me

• Physics -

Phy, yes second problem. Unfortunately, I could also not get it. Does someone know the right formula please?

• Physics -

Do you know 1st c) and d) ??
And 3rd problem??

• Physics -

1st) c) 1.5*V
d) t=-ln(0.25)*2*R*C

• Physics -

• Physics -

Thanks lo, can you help with Problem 2?

• Physics -

Io,
The formula Q1 d)t=-ln(0.25)*2*R*C doesn't work for me, you can check it, there can be there a mistake is?

• Physics -

it does not work for me also

• Physics -

has anyone figured out 1d yet???/ PLEASE!? I really need it!

• Physics -

1 d)
The correct Formula is
t=-ln(0.25)*R*C

Where R is the thevenin resistance in the capacitor
Where Rth = [R||R + R]

• Physics -

GR, the answer isn't coming with that formula!

• Physics -

Robbo, can you post your values plz?

• Physics -

hi GR, what is your values plz for Q1

• Physics -

Second problem last formula please? I used T = 2*pi*sqr(C*L), but it gives wrong answer. T/ 4 as well.....

• Physics -

03 do you have second proble formula d) and e) please?

• Physics -

03 this was mentioned by Slylar in another thread but did not work for me for f) problem 2:
And for 2f is sqrt(2c*capacitor)*pi/2

do you have formula for problem 2) d) and e) please?

• Physics -

d)L*I^2/2
e)Sqr(2*C*U)

• Physics -

I got the answer, if you give the correct answer for 1c,1d. Thnx

• Physics -

FLu what is c* capacitor ?!

• Physics -

GR my values for Ques1 d part are V=25 C=401 R=37

• Physics -

Sorry 03, I think Sylar meant the answer from c) and the capacitor value.
I copy the message below:
Ah, ok. For d)You have the inductance for answer 2b. And the time for 2c.
2b*2c^2/2.
And for 2f is sqrt(2c*capacitor)*pi/2

can you tell me the value for I and L please in d) and also what is value U in e) please 03?

• Physics -

TA please give ans or formula for any ques tion you have got. 1c is 1.5*V V is volatage of the battery.

• Physics -

I got the answer, if you give the correct answer for 1d. Thnx

• Physics -

Pls. tell any one ans I am working on 1d

• Physics -

• Physics -

Can you give me the formula then TA please for d) and e) please?

• Physics -

1D needs TH RESISTANCE . pLS EXPRESSION
for TH Rx for ths circuit. wrong answers given

• Physics -

TA I meant Problem 2 d) and e) not 1. Do you have them please?

• Physics -

• Physics -

Problem 2 d) and e) and f) please? Something dioes not work

• Physics -

1.d .375 (R*C)

2.d 0
2.e 0.125

• Physics -

You have to PAY Buddy, just like on Campus.

• Physics -

anyone get #6???