Tuesday

September 16, 2014

September 16, 2014

Posted by **Annoyingmous** on Wednesday, May 22, 2013 at 9:20pm.

What will the magnetic field strength be inside the air gap? Express your answer in Tesla. Assume that the magnetic field is azimuthal (i.e. points around the circle formed by the steel) everywhere and d≪ the radius of the electromagnet.

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**hmmmm**, Thursday, May 23, 2013 at 9:46amans=1.44

for people with other values use this

B=(meu not*N*I)/((2*pi*R/km) +d)

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**Anonymous**, Thursday, May 23, 2013 at 10:44amThanx hmmmm, Other problems? (1,2,3,5 & 6)

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**^_ ^**, Thursday, May 23, 2013 at 11:22amProblem 3:

a)

r = 0

theta = 0

k = (Q_0*(1+2*T/T)) / (Pi*R^2*epsilon_0)

b)

r = 0

theta = mu_0*I*r/(2*Pi*R^2)

k = 0

c)

r = - 1/mu_0 * E X B <- note the sign.

theta = 0

k = 0

d), e) -Q*I*D/(Pi*R^2*epsilon_0)

Note that Q = Q_0*(1+2T/T) and I = dQ/dt

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**Anonymous**, Thursday, May 23, 2013 at 12:48pmThanks, ^_ ^

What about probs. 1, 2 and 5 ?

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**FLu**, Thursday, May 23, 2013 at 3:18pmCan somebody tell me what the value of R is?

thanks

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**Mag**, Thursday, May 23, 2013 at 3:21pmVAlue of I please

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**Mag**, Thursday, May 23, 2013 at 3:26pmIs I = radius(a)/distance(d)?

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**Annoyingmous**, Thursday, May 23, 2013 at 4:21pmthe parentheses are confusing me for (Q_0*(1+2*T/T))

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**T**, Thursday, May 23, 2013 at 4:34pmWHat is value of R please?

cannot figure out.

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**Hu**, Friday, May 24, 2013 at 1:31amPlease tell what the value for R is?

Is I = radius(a)/distance(d)?

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**Anonymous**, Friday, May 24, 2013 at 4:12amI=dQ/dt

and the value of R is a i.e. radius of the circular plate of the capacitor.

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**Anonymous**, Friday, May 24, 2013 at 4:14amformula for question d and e?? answer is wrong while using formula given by ^_^. can u recheck the formula??

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**Tia**, Friday, May 24, 2013 at 4:26amThanks Anonymous. sorry for question but which values are dQ and dt please in the question?

Is dQ=radius of circular plate

and dt=distance separated=2.2mm?

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**sat**, Friday, May 24, 2013 at 7:05amCan someone explain the formula:

""for people with other values use this

B=(meu not*N*I)/((2*pi*R/km) +d)""

what is I and "not"

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**Dr. Slump**, Friday, May 24, 2013 at 7:15amI is the current dQ/dt and meu not is 4*pi*1E-7

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**sat**, Friday, May 24, 2013 at 7:21amI got it ...

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**hmmmm**, Friday, May 24, 2013 at 7:38amsorry it is meu_0 and I is given in question

meu=4*pi*1E-7 as mentioned by other friends

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**sat**, Friday, May 24, 2013 at 7:57amRADIATION PRESSURE ON THE EARTH? Can comeone help with this?

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**Anonymous**, Friday, May 24, 2013 at 7:58am@TIA: Q is given in the question. Differentiate this Q(t) with respect to time an find the current.

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**hmmmm**, Friday, May 24, 2013 at 8:22amradiation pressure qn

a) 5.823e8

b) 3.56e22

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**FLu**, Friday, May 24, 2013 at 8:44amThanks guys, did somebody have formula for problem 1 and 2?

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**Tia**, Friday, May 24, 2013 at 9:14amThanks Anonymous, I still have issues identifying I=dQ/dt

could you plug in the numbers from the above example please so I can see?

From the above example it seem like this is this correct?

Q= Q_0*(1+2T/T)

d=separated distance in my case 6mm

t=time 2

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**Yu**, Friday, May 24, 2013 at 9:24amCan someone explain with values for I = dQ/dt please?

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**Anonymous**, Friday, May 24, 2013 at 10:01am@TIA: Q=Q_0*(1+t/T)

differentiate with respect to t,

dQ/dt=Q_0/T=I

Simply plugin the values of Q_0 and T and you get the current.

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**Tia**, Friday, May 24, 2013 at 10:56amMany thanks Anonymous!

Could you tell me what the values for E, X and B stand for in:

r = - 1/mu_0 * E X B

and the D value for e) -Q*I*D/(Pi*R^2*epsilon_0) ?

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**trustee**, Friday, May 24, 2013 at 12:46pmwhat is D and r? any idea . also EXB does it come out negative or positive

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**Anonymous**, Friday, May 24, 2013 at 12:57pmformula 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)

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**hmmmm**, Friday, May 24, 2013 at 1:02pmformula 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)

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**FLu**, Friday, May 24, 2013 at 1:15pmThanks guys, what is value A please?

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**hmmmm**, Friday, May 24, 2013 at 1:21pmpi*r^2

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**hmmmm**, Friday, May 24, 2013 at 1:22pmand in neumerator I its current and in denominator its l length

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**FLu**, Friday, May 24, 2013 at 1:27pmTHanks hmmmm, r is the radius b=0.2 cm right?

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**Hu**, Friday, May 24, 2013 at 11:58pmWhat is value for 'r' please?

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**Hu**, Saturday, May 25, 2013 at 12:00amBy the way guys, is this an error?

L=meu_0*N^2*A//l

Does it not mean:

L=meu_0*N^2*A*I/l or

L=meu_0*N^2*A/l ?

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**FLu**, Saturday, May 25, 2013 at 1:03amOnly c) worked for me, I am surely making some wrong with a), c) and d).

Did someone figure out with above formula please?

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**FLu**, Saturday, May 25, 2013 at 1:04ama), b) and d) I meant.

Help appreciated

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**fa**, Saturday, May 25, 2013 at 3:19amany hint on 2f? 6?

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**Anonymous**, Saturday, May 25, 2013 at 4:31amConsider a charging capacitor made out of two identical circular conducting plates of radius a=11 cm. The plates are separated by a distance d=2 mm (see figure below, note that d≪a). The bottom plate carries a positive charge

Q(t)=+Q0(1+tT)

with Q0=4e-06 C and T=0.002 sec, and the top plate carries a negative charge −Q(t) . The current through the wire is in the positive k€-direction. You may neglect all edge effects.

(a) Calculate the components of the electric field (in V/m) inside the capacitor for t=2T

(b) Calculate the components of the magnetic field B(r,t) (in Teslas) at time t=2T inside the capacitor at a distance r=1.1 cm from the central axis of the capacitor.

(c) Calculate the components of the Poynting vector S⃗ (r,t) (in W/m2) at time t=2T between the plates at a distance r=1.1 cm from the central axis of the capacitor.

(d) What is the flow of energy (in W) into the capacitor at time t=2T ?

(e) How fast is the energy stored in the electric field changing (i.e. what is the rate of change in W) within the capacitor at time t=2T ?

please answer i have only one submission

please help.

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**Sat**, Saturday, May 25, 2013 at 7:42amRegarding Q2, e and f -> The energy is 1/2*Q^2*C. We have Q at this oment of time and C comes out from the geometry of the capacitor. Now, guess what - it's wrong. Any ideas?

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**BoobleGum**, Saturday, May 25, 2013 at 8:44amQ2 e) :

W(c) = W(l) |=>

(q^2)/(2C) = (L*(I^2))/2 |=>

q = sqrt[C*L*(I^2)]

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**Sat**, Saturday, May 25, 2013 at 8:51amsorry i meant Q3, d and e

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**BoobleGum**, Saturday, May 25, 2013 at 9:02amQ2 (f):

t = (pi*sqrt(LC))/2

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**fa**, Saturday, May 25, 2013 at 9:08amthanks BoobleGum. Any hint for Q6?

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**BoobleGum**, Saturday, May 25, 2013 at 9:12amQ3 (e), (d):

(Q_0*(1+t/T)*I*d)/(pi*(R^2)*E_0),

E_0 = 8.85 * 10^(-12)

I = Q_0/T

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**BoobleGum**, Saturday, May 25, 2013 at 9:17amfa, I only half made it

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**BoobleGum**, Saturday, May 25, 2013 at 9:21amfa, how Q1 d) is solved?

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**FLu**, Saturday, May 25, 2013 at 9:38amBooblegum, this was mentioned in another thread:

d) t=-ln(0.25)*2*R*C

could you help with question 2 a, b, c please as I think there is something wrong with the formula or I am making a mistake.

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**FLu**, Saturday, May 25, 2013 at 9:42ama)B=meu_0*N*I/l

b)L=meu_0*N^2*A//l

c)I=V/R

d)U=1/2(LI^2)

I get only c) right

could somebody help me with the values, mine is as following:

A solenoid has N=2070.0 turns, length d=40 cm , and radius b= 0.2 cm. The solenoid is connected via a switch, S1, to an ideal voltage source with electromotive force e= 9 V and a resistor with resistance R= 39 Ohm . Assume all the self-inductance in the circuit is due to the solenoid. At time t=0, S1 is closed while S2 remains open.

a)When a current I=0.138 A is flowing through the outer loop of the circuit (i.e. S1 is still closed and S2 is still open), what is the magnitude of the magnetic field inside the solenoid (in Tesla)?

Thanks

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**BoobleGum**, Saturday, May 25, 2013 at 9:54amt=-ln(0.25)*2*R*C -this formula at me isn't accepted

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**BoobleGum**, Saturday, May 25, 2013 at 10:03amFLu, at me so:

Q2:

a) B = mu_0*I*N/(l), here l = length

b) L = mu_0*((N/L)^2)*V, V = (pi*R^2)*d

c) I = V/R

D) U = (L*I^2)/2

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**BoobleGum**, Saturday, May 25, 2013 at 10:06amGive me the correct formula for Q1 d)

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**FLu**, Saturday, May 25, 2013 at 10:07amTHanks Booblegum, will try it out again and report back.

Booblegum I did not try the first question out with the formula, this was mentioned by another one and I thought it works, just look at my profile under:

Thanks lo, can you help with Problem 2?

This were you can find what was posted and maybe also ask Io. Otherwise, can somebody give formula for question 1)d) please or was somebody successful with abvove formula?

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**BoobleGum**, Saturday, May 25, 2013 at 10:12amthanks)

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**FLu**, Saturday, May 25, 2013 at 10:15amBooblegum, what is L value please? I cannot identify.

thanks

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**FLu**, Saturday, May 25, 2013 at 10:16amIn b) mu_0*((N/L)^2)*V

I don't know which value is L?

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**BoobleGum**, Saturday, May 25, 2013 at 10:27amlength (l);

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**FLu**, Saturday, May 25, 2013 at 10:42amBooblegum thanks, I get a) but b) and d) not.

b) L = mu_0*((N/L)^2)*V, V = (pi*R^2)*d

Is V the epsilon value or calculated by

V = (pi*R^2)*d?

I put my values in but it does not give right answer.

1.25663706*10^-6*((2079/0.42)^2)*9

V = (pi*R^2)*d

does d=length?

d)U = (L*I^2)/2

Is L=length

and I=current or

am I missing something again?

thanks again and sorry for questions

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**BoobleGum**, Saturday, May 25, 2013 at 10:56am)) так ты русский?) Я ж нихера по английски не понимаю, и не знаю как тебе ответить. Давай завтра может если получится объясню.

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**BoobleGum**, Saturday, May 25, 2013 at 11:07amSor! tomorrow I will explain

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**FLu**, Saturday, May 25, 2013 at 11:08amTHanks BoobleGum, see you tomnorrow!

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**Anonymous**, Saturday, May 25, 2013 at 12:16pmhow to find R in problem 3?

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**robbo**, Saturday, May 25, 2013 at 11:52pmGuys how do we go about the Electromagnetic wave question???

Can anybody help??????

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**FLu**, Sunday, May 26, 2013 at 6:48amBoobleGum if you have time, could you help with this one below please?

b) L = mu_0*((N/L)^2)*V, V = (pi*R^2)*d

Is V the epsilon value or calculated by

V = (pi*R^2)*d?

I put my values in but it does not give right answer.

1.25663706*10^-6*((2079/0.42)^2)*9

V = (pi*R^2)*d

does d=length?

d)U = (L*I^2)/2

Is L=length

and I=current or

am I missing something again?

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**BoobleGum**, Sunday, May 26, 2013 at 8:13amFLu,

b) I think it`s rigth, but

in formula mu_0*((N/L)^2)*V,

value V is volume = (circle area) * (length solenoid),

d=length, pi*R*R = circle.

I have V = pi*0.001*0.001*0.14 = 4.39822971503e-07

R = radius = 0.1sm = 0.001m

d = length = 14sm = 0.14m

L = 1.26*10^(-6)*[(609/0.14)^2]*4.39822971503e-07

= 0.00001048109706

PS Lewin swears therefore more I won't explain, sor)

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**hmmmm**, Sunday, May 26, 2013 at 8:58amyes FLu you are doing it wrong

L=(mu_0*A*N^2)/L

send me your values i'll post your answer

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**BoobleGum**, Sunday, May 26, 2013 at 9:10amhmmmm, you me certainly forgive, but you are a little fool

mu_0*((N/L)^2)*pi*(R^2)*d

equally

mu_0*A*N^2)/L

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**hmmmm**, Sunday, May 26, 2013 at 9:15amFLu your ans of 2b is

1.69e-4

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**FLu**, Sunday, May 26, 2013 at 9:16amThanks BoobleGum and hmmmm

b) worked now with BoobleGum's great explaination

Hoever, still have problem with d.

d)U = (L*I^2)/2

Here L is the length described as d?

and I is the current described in question a)?

The result comes wrong with that formula or the value I understand is not the one to put in.

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**BoobleGum**, Sunday, May 26, 2013 at 9:37amTatar, может ты знаешь как найти время в первом вопросе?

У меня это последнее задание осталось, только вот не решается.

И кстати заметил у пиндосов только один матюк, только Левин его с разными окончаниями применяет.

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**SyLaR**, Sunday, May 26, 2013 at 9:53amFlu, the energy is for a long time. That's means that is the I maximun.

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**SyLaR**, Sunday, May 26, 2013 at 9:54amDo you have the rigth answaer for 2e) about the capacitor? The I max is for the ans of 2c.

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**SyLaR**, Sunday, May 26, 2013 at 9:56amAnd, in this formula :

(mu_0*N*I)/((2*pi*R/km) +d)

what d means? the volume? so, i mean Croos section x air grap?

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**FLu**, Sunday, May 26, 2013 at 9:56amSyLaR no sorry, have not figured d) e and f) out.

Could you tell me quick with values assocated with I and L?

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**FLu**, Sunday, May 26, 2013 at 9:57amI thought this is formula for d)

d)U = (L*I^2)/2 ?

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**SyLaR**, Sunday, May 26, 2013 at 9:59amAh, ok. You have the inductance for answer 2b. And the time for 2c.

So. The answer will be

2b*2c^2/2.

And for 2f is sqrt(2c*capacitor)*pi/2

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**SyLaR**, Sunday, May 26, 2013 at 10:00amYes flu, that the formula. L*i^2/2

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**FLu**, Sunday, May 26, 2013 at 10:19amSyLaR it does not deliver right answer for d and f.

does it mean 2* the answer of b and c?

or maybe a bracket problem, could you check please?

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**An**, Sunday, May 26, 2013 at 11:03amcan anyone help me with question 6?

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**Hu**, Sunday, May 26, 2013 at 11:10amFor me didnt work SyLaR. did work for someone the formula for d) and f)?

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**BoobleGum**, Sunday, May 26, 2013 at 11:35amTatar,

пятое

а, напряжение в квадрате поделенное на два сопротивления. напряжение это число перед синусом

б, тот же ответ только деленный еще на два.

шестое

а, лямбда это два пи умноженное на скорость света и поделенное на число перед т.

б, это число перед т поделенное на два пи

А нулевое это б (магнитное поле) умноженное на минус один и умноженное на скорость света

к икс и к игрик равны нулю к зэд равно первому аргументу внутри синуса

омега это число перед т с плюсом

полинг вектор это Б умноженное на е (електрич поле) и деленное на два мю

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**P**, Sunday, May 26, 2013 at 12:09pmIn Q4 what is Km Is it kM=2500

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**P**, Sunday, May 26, 2013 at 12:26pmhmmmm pls. find ans of the below. An electromagnet has a steel core (κM≈ 2500) with an approximately circular cross sectional area of 5.0 cm2. The radius of the magnet is 10.0 cm; there is a small air gap of only 2.6 mm (see sketch). The current through the magnet's N= 120-turn coil is 34 A.

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**P**, Sunday, May 26, 2013 at 12:41pmhmmmm pls. post ans for this question pls I have got only one chance left.

A solenoid has N=1863.0 turns, length d=46 cm , and radius b=0.4 cm, (b<<d) . The solenoid is connected via a switch, S1 , to an ideal voltage source with electromotive force ϵ=3 V and a resistor with resistance R=41 Ohm . Assume all the self-inductance in the circuit is due to the solenoid. At time t=0 , S1 is closed while S2 remains open.

(a) When a current I=4.39e-2 A is flowing through the outer loop of the circuit (i.e. S1 is still closed and S2 is still open), what is the magnitude of the magnetic field inside the solenoid (in Tesla)?

unanswered

(b) What is the self-inductance L of the solenoid (in H)?

unanswered

(c) What is the current (in A) in the circuit a very long time (t>>L/R) after S1 is closed? .

unanswered

(d) How much energy (in J) is stored in the magnetic field of the coil a very long time (t>>L/R) after S1 is closed?

unanswered

For the next part, assume that a very long time (t>>L/R) after the switch S1 was closed, the voltage source is disconnected from the circuit by opening switch S1. Simultaneously, the solenoid is connected to a capacitor of capacitance C=651 μF by closing switch S2. Assume there is negligible resistance in this new circuit.

(e) What is the maximum amount of charge (in Coulombs) that will appear on the capacitor?

unanswered

(f) How long does it take (in s) after S1 is opened and S2 is closed before the capacitor first reaches its maximum charge?

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**Physics**, Sunday, May 26, 2013 at 12:42pmAny one please ans this answer.

The circuit below consists of three identical resistors each with resistance R=37 Ohm, two identical batteries with emfs E=25 V, and a capacitor with capacitance C=401 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=

unanswered

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

i2=

unanswered

i3=

unanswered

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

VC=

unanswered

(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=

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**P**, Sunday, May 26, 2013 at 1:15pmCan any one pls put the correct formulas in order.

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**P**, Sunday, May 26, 2013 at 1:17pmQ6 ans can be solved by HW7 And HW8

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**SyLaR**, Sunday, May 26, 2013 at 5:03pmIn problem 2:

1/2*L*I^2= Total Energy.

And, 1/2*C*V^2 = Total energy. (Same of the first)

Here you get V.

And the energy in coulumb = C * V

Thats the answer of the p2. e)

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**Annoyingmous**, Sunday, May 26, 2013 at 5:23pmquestion 7 anyone?

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**Annoyingmous**, Sunday, May 26, 2013 at 5:23pmsorry i mean question 6, question 6 anyone?

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**afzal**, Sunday, May 26, 2013 at 10:46pmQ1 last part.....neyone ??? I knw the formula -ln(0.25)*2*R*C, where R= Rth.....what is the formula for Rth ???

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**BoobleGum**, Monday, May 27, 2013 at 2:29amFor q1 (d):

find the general resistance of the scheme on the condenser, and there will be to you a happiness

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**BoobleGum**, Monday, May 27, 2013 at 2:30amAnd naturally set up him in a formula given above

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**Reuben**, Monday, May 27, 2013 at 10:07amA circuit consists of a resistor of R=5 Ω, a capacitor of C=7 μF, and an ideal self-inductor of L=0.08 H. All three are in series with a power supply that generates an EMF of 6sin(ωt) Volt. The internal resistance of both the power supply and the inductor are negligibly small. The system is at resonance.

part b)

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**W**, Monday, May 27, 2013 at 2:27pmanyone get #6

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**tolako**, Wednesday, June 5, 2013 at 10:47amWhat would be the radius (φmax, in degrees) of a glass bow? The glass

What would be the radius (φmax, in degrees) of a glass bow? The glass beads have an index of refraction n=1.5. We spread them out on the ground and we observe a glass bow as the sun is high in the sky.

**Answer this Question**

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