Posted by Annoyingmous on .
An electromagnet has a steel core (κM≈ 2500) with an approximately circular cross sectional area of 7.0 cm2. The radius of the magnet is 12.0 cm; there is a small air gap of only 2.2 mm (see sketch). The current through the magnet's N= 120turn coil is 24 A.
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.

Physics 
hmmmm,
ans=1.44
for people with other values use this
B=(meu not*N*I)/((2*pi*R/km) +d) 
Physics 
Anonymous,
Thanx hmmmm, Other problems? (1,2,3,5 & 6)

Physics 
^_ ^,
Problem 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 
Physics 
Anonymous,
Thanks, ^_ ^
What about probs. 1, 2 and 5 ? 
Physics 
FLu,
Can somebody tell me what the value of R is?
thanks 
Physics 
Mag,
VAlue of I please

Physics 
Mag,
Is I = radius(a)/distance(d)?

Physics 
Annoyingmous,
the parentheses are confusing me for (Q_0*(1+2*T/T))

Physics 
T,
WHat is value of R please?
cannot figure out. 
Physics 
Hu,
Please tell what the value for R is?
Is I = radius(a)/distance(d)? 
Physics 
Anonymous,
I=dQ/dt
and the value of R is a i.e. radius of the circular plate of the capacitor. 
Physics 
Anonymous,
formula for question d and e?? answer is wrong while using formula given by ^_^. can u recheck the formula??

Physics 
Tia,
Thanks 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? 
Physics 
sat,
Can 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" 
Physics 
Dr. Slump,
I is the current dQ/dt and meu not is 4*pi*1E7

Physics 
sat,
I got it ...

Physics 
hmmmm,
sorry it is meu_0 and I is given in question
meu=4*pi*1E7 as mentioned by other friends 
Physics 
sat,
RADIATION PRESSURE ON THE EARTH? Can comeone help with this?

Physics 
Anonymous,
@TIA: Q is given in the question. Differentiate this Q(t) with respect to time an find the current.

Physics 
hmmmm,
radiation pressure qn
a) 5.823e8
b) 3.56e22 
Physics 
FLu,
Thanks guys, did somebody have formula for problem 1 and 2?

Physics 
Tia,
Thanks 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 
Physics 
Yu,
Can someone explain with values for I = dQ/dt please?

Physics 
Anonymous,
@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. 
Physics 
Tia,
Many 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) ? 
Physics 
trustee,
what is D and r? any idea . also EXB does it come out negative or positive

Physics 
Anonymous,
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 
hmmmm,
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 
FLu,
Thanks guys, what is value A please?

Physics 
hmmmm,
pi*r^2

Physics 
hmmmm,
and in neumerator I its current and in denominator its l length

Physics 
FLu,
THanks hmmmm, r is the radius b=0.2 cm right?

Physics 
Hu,
What is value for 'r' please?

Physics 
Hu,
By 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 ? 
Physics 
FLu,
Only c) worked for me, I am surely making some wrong with a), c) and d).
Did someone figure out with above formula please? 
Physics 
FLu,
a), b) and d) I meant.
Help appreciated 
Physics 
fa,
any hint on 2f? 6?

Physics 
Anonymous,
Consider 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=4e06 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 kˆdirection. 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. 
Physics 
Sat,
Regarding 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?

Physics 
BoobleGum,
Q2 e) :
W(c) = W(l) =>
(q^2)/(2C) = (L*(I^2))/2 =>
q = sqrt[C*L*(I^2)] 
Physics 
Sat,
sorry i meant Q3, d and e

Physics 
BoobleGum,
Q2 (f):
t = (pi*sqrt(LC))/2 
Physics 
fa,
thanks BoobleGum. Any hint for Q6?

Physics 
BoobleGum,
Q3 (e), (d):
(Q_0*(1+t/T)*I*d)/(pi*(R^2)*E_0),
E_0 = 8.85 * 10^(12)
I = Q_0/T 
Physics 
BoobleGum,
fa, I only half made it

Physics 
BoobleGum,
fa, how Q1 d) is solved?

Physics 
FLu,
Booblegum, 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. 
Physics 
FLu,
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)
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 selfinductance 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 
Physics 
BoobleGum,
t=ln(0.25)*2*R*C this formula at me isn't accepted

Physics 
BoobleGum,
FLu, 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 
Physics 
BoobleGum,
Give me the correct formula for Q1 d)

Physics 
FLu,
THanks 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? 
Physics 
BoobleGum,
thanks)

Physics 
FLu,
Booblegum, what is L value please? I cannot identify.
thanks 
Physics 
FLu,
In b) mu_0*((N/L)^2)*V
I don't know which value is L? 
Physics 
BoobleGum,
length (l);

Physics 
FLu,
Booblegum 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 
Physics 
BoobleGum,
)) òàê òû ðóññêèé?) ß æ íèõåðà ïî àíãëèéñêè íå ïîíèìàþ, è íå çíàþ êàê òåáå îòâåòèòü. Äàâàé çàâòðà ìîæåò åñëè ïîëó÷èòñÿ îáúÿñíþ.

Physics 
BoobleGum,
Sor! tomorrow I will explain

Physics 
FLu,
THanks BoobleGum, see you tomnorrow!

Physics 
Anonymous,
how to find R in problem 3?

Physics 
robbo,
Guys how do we go about the Electromagnetic wave question???
Can anybody help?????? 
Physics 
FLu,
BoobleGum 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? 
Physics 
BoobleGum,
FLu,
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 = 4.39822971503e07
R = radius = 0.1sm = 0.001m
d = length = 14sm = 0.14m
L = 1.26*10^(6)*[(609/0.14)^2]*4.39822971503e07
= 0.00001048109706
PS Lewin swears therefore more I won't explain, sor) 
Physics 
hmmmm,
yes FLu you are doing it wrong
L=(mu_0*A*N^2)/L
send me your values i'll post your answer 
Physics 
BoobleGum,
hmmmm, 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 
Physics 
hmmmm,
FLu your ans of 2b is
1.69e4 
Physics 
FLu,
Thanks 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. 
Physics 
BoobleGum,
Tatar, ìîæåò òû çíàåøü êàê íàéòè âðåìÿ â ïåðâîì âîïðîñå?
Ó ìåíÿ ýòî ïîñëåäíåå çàäàíèå îñòàëîñü, òîëüêî âîò íå ðåøàåòñÿ.
È êñòàòè çàìåòèë ó ïèíäîñîâ òîëüêî îäèí ìàòþê, òîëüêî Ëåâèí åãî ñ ðàçíûìè îêîí÷àíèÿìè ïðèìåíÿåò. 
Physics 
SyLaR,
Flu, the energy is for a long time. That's means that is the I maximun.

Physics 
SyLaR,
Do you have the rigth answaer for 2e) about the capacitor? The I max is for the ans of 2c.

Physics 
SyLaR,
And, 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? 
Physics 
FLu,
SyLaR no sorry, have not figured d) e and f) out.
Could you tell me quick with values assocated with I and L? 
Physics 
FLu,
I thought this is formula for d)
d)U = (L*I^2)/2 ? 
Physics 
SyLaR,
Ah, 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 
Physics 
SyLaR,
Yes flu, that the formula. L*i^2/2

Physics 
FLu,
SyLaR 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? 
Physics 
An,
can anyone help me with question 6?

Physics 
Hu,
For me didn't work SyLaR. did work for someone the formula for d) and f)?

Physics 
BoobleGum,
Tatar,
ïÿòîå
à, íàïðÿæåíèå â êâàäðàòå ïîäåëåííîå íà äâà ñîïðîòèâëåíèÿ. íàïðÿæåíèå ýòî ÷èñëî ïåðåä ñèíóñîì
á, òîò æå îòâåò òîëüêî äåëåííûé åùå íà äâà.
øåñòîå
à, ëÿìáäà ýòî äâà ïè óìíîæåííîå íà ñêîðîñòü ñâåòà è ïîäåëåííîå íà ÷èñëî ïåðåä ò.
á, ýòî ÷èñëî ïåðåä ò ïîäåëåííîå íà äâà ïè
À íóëåâîå ýòî á (ìàãíèòíîå ïîëå) óìíîæåííîå íà ìèíóñ îäèí è óìíîæåííîå íà ñêîðîñòü ñâåòà
ê èêñ è ê èãðèê ðàâíû íóëþ ê çýä ðàâíî ïåðâîìó àðãóìåíòó âíóòðè ñèíóñà
îìåãà ýòî ÷èñëî ïåðåä ò ñ ïëþñîì
ïîëèíã âåêòîð ýòî Á óìíîæåííîå íà å (åëåêòðè÷ ïîëå) è äåëåííîå íà äâà ìþ 
Physics 
P,
In Q4 what is Km Is it kM=2500

Physics 
P,
hmmmm 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= 120turn coil is 34 A.

Physics 
P,
hmmmm 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 selfinductance in the circuit is due to the solenoid. At time t=0 , S1 is closed while S2 remains open.
(a) When a current I=4.39e2 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 selfinductance 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? 
Physics 
Physics,
Any 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= 
Physics 
P,
Can any one pls put the correct formulas in order.

Physics 
P,
Q6 ans can be solved by HW7 And HW8

Physics 
SyLaR,
In 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) 
Physics 
Annoyingmous,
question 7 anyone?

Physics 
Annoyingmous,
sorry i mean question 6, question 6 anyone?

Physics 
afzal,
Q1 last part.....neyone ??? I knw the formula ln(0.25)*2*R*C, where R= Rth.....what is the formula for Rth ???

Physics 
BoobleGum,
For q1 (d):
find the general resistance of the scheme on the condenser, and there will be to you a happiness 
Physics 
BoobleGum,
And naturally set up him in a formula given above

Physics 
Reuben,
A circuit consists of a resistor of R=5 Ω, a capacitor of C=7 μF, and an ideal selfinductor 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) 
Physics 
W,
anyone get #6

Physics 
tolako,
What 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.