# Physics

An infinite straight wire carrying a current I=5 A flowing to the right is placed above a rectangular loop of wire with width w=11 cm and length L=27 cm, as shown in the figure below. The distance from the infinite wire to the closest side of the rectangle is h=1.7 cm. The loop of wire has resistance R=0.31 Ohm.

(a) What is the magnitude (in Tesla) of the magnetic field due to the infinite wire at the point P in the rectangular loop, a distance r=3.2 cm from the wire (see figure).

In which direction does it point?

(b) Calculate the magnitude of the magnetic flux (in Tesla  m2) through the rectangular loop due to the magnetic field created by the infinite wire.

(c) Suppose the current in the infinite wire starts increasing in time according to I=bt, with b=50 Amps/sec. What is the magnitude (in Amps) of the induced current in the loop? Neglect any contribution to the magnetic flux through the loop due to the magnetic field created by the induced current.

(d) What is the direction of this current flow?

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1. a) B = mu_0*I/(2*Pi*r)

b) phi = (mu_0*I*L/(2*Pi))*ln(1+w/h)

c) i = (-1/R)*(mu_0*L)/(2*Pi)*ln(1+w/h)*(di/dt)

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2. What is di/dt ??

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3. Phy, it's the b in the variation I=bt. Just use the b value in the problem for (di/dt)

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4. Thanks, can u tell me the solutions of 1,4,6,9,10,11,12?

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5. the C is wrong for me using the b in di/dt

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6. Have you guys gt 3,5,7,8,9,10,11,12...????? Let's help each other and get this done guys!!

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7. C is wrong ...

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8. Some people haven't done even one question.

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9. I wonder if some people understand the subject at all. It is an insult to the lecturer.

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10. Hey boss, how did u come across this topic if you have not googled the question? It's obvious that you cheat also!

BTW - for C just use the value for b (the one in the question) b=(di/dt)

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11. Hey guys, what abput prob. 10?

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12. 10, b) how to solve

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Q3 a=0 last part =0

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16. Anyone, can help with questions:

11 c)
10 b)
8 d,e,f)
5 b,d,e)

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17. 11 a)
q/(4*pi*E_0*(r^2)*k)

11 b)
q*k/(r^2)

11 d) 0

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18. anyone for question 7 please

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19. Hi BG, can you put the results for 8 a, b,c?

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21. anyone for question 3 please??????

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22. 5 e)
v= m*g*R/(B^2*W^2)

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23. 8 a)
E = (st)/(S*E_0)
S = Area

8 b) E*d

8 c)
C = E*E_0*S/d

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24. S = pi(b^2 - a^2)

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25. Jack, did you solve anything else from this list:
11 c)
10 b)
8 d,e,f)
5 b,d)

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26. me, I will exchange solution 8 on 7)

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27. me, a = lambda/0.5
d = lambda/0.125

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28. denaminator may be different, it depends on drawing

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29. How I can know my denominator watching my grahp BG?

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30. prob 8

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31. I think drawings at all identical so don't worry

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32. BG sorry don't have 8 yet, i'll post it as soon as i solve it and thanks for 7

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33. i have 5 do you still need 5b and 5d

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34. BG,

8 d)

B= mu_0*(r^2-a^2)*s/(2*r*pi*(b^2-a^2))

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35. BG, do you have 10 c and d?

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37. 8 e)
t*s^2/2*PI^2*(b^2-a^2)

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38. 5) a)=B(l-W)z(t)
b)=(B*V*W)/R
c)=(B^2*V*W^2)/R
d)= (M*g*R)/(B^2*W^2)

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40. 8 f)
Result of e multiplied by 2*pi*b*d

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41. i'm conufsed about the parentheses that might havve been omitted in OVNI's answer to 8e....

t*s^2/(2*PI^2*(b^2-a^2) )

Is this correct?

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42. I think a b is missing!

t*s^2/(2*PI^2*b*(b^2-a^2) )

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43. Sorry, it's

(t*s^2)/(2*PI^2*b*(b^2-a^2))

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44. 8f, 8e solutions aren't working out as given by OVNI and Jack... help guys?

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45. Please 11 c) and 10!

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46. Jack, 11c is 0.5*L*I^2

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47. Thank you so much!
Question 10??

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48. Sorry, but I posted as I worked and I got a green check mark.
Please any one 9 and 10

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49. Sorry I meant 10c is 0.5*L*I^2.... the LC circuit sum, does anybody have 10 b and d??

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50. how do you get 11 b and c???

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51. Roboo, why in your 11c you use L, and I?????

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52. I meant 10c OVNI! Mistake... SOrry!

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54. 9b????

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55. robbo, the same that 9 a)

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56. 9b = 9a, E1 = V/d1 and E2 = V/d2

9c)try with charge conservation

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57. robbo 10 b)

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58. 11 b)
q*9*(10^9)/r^2
r = distance from the origin

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59. 10 b) 10 d) and 11 c) please!!!!

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60. 5A doesn't seem to work

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61. Please give ans for Q5 for values I am getting them last chance please

What is the total magnetic flux through the loop (in Tesla m ) when is 62 cm. Include only the magnetic flux associated with the external field (i.e. ignore the flux associated with the magnetic self-field generated by the current in the wire loop). Note that you do not need to calculate or know at what time the loop is at this location.

incorrect

(b) Using Faraday's Law and Ohm's Law, find the magnitude (in Amps) of the induced current in the bar at the time when 1.00 m/sec. Note that you do not need to calculate or know at what time the loop has this speed.

incorrect

(c) Which way does the current flow around the loop, clockwise or counterclockwise?

Status: correct

(d) What is the total magnetic force (in Newtons) on the rigid wire loop when 1.00 m/sec? Again, ignore any effects due to the self magnetic field.

direction:
Status: correct

magnitude (in Newtons):

incorrect

(e) What is the magnitude of the terminal speed (in m/sec) of the loop (i.e. the speed at which the loop will be moving when it no longer accelerates)?

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62. 8 e)

poling vector = E*B/mu_0 = ??

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63. it's correct ?

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64. P, phi=B*w*(L-z)
|em|=|dphi/dt|=B*w*V
i=|em|/R=B*w*V/R
F=watt/ms^-1=(|em|^2/R)*1/V

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65. BG, OK

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67. 10b)= frequency that abs(i(t))=max

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68. f= 1/(2*pi*sqrt(L*C))?

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70. i(t)=I0*cos(w*t) and abs(i(t))=max if
w*t=k*pi, for k=1=>t1=pi/w
f=1/t1=w/pi=1/(pi*sqrt(L*C))

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71. 124, i have E and B correct
but

pointing vector with formula E*B/mu_0, mu_0 = 4*pi*10^(-7), incorrect.

pliz, tell where is error?

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72. 10d)=>average p=v*i on [0,3*t1]

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73. BG, S=E*B/mu_0
= 1/(2*pi^2*b)*s^2*t/(b^2-a^2)

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74. 10b) f=1/t1=w/pi=1/(pi*sqrt(L*C))

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75. BG, B(r=b) = mu_0*s/(2*pi*b)is not the the previous B(r)

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76. 124, thanks a lot, you the man. )

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79. in 10d for P=V*I, where do we get V from???

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80. robbo, v=Ldi/dt
P_mean=1/(3T-0)*int(v*i,0,3*T)
T=2*pi*sqrt(L*C)

11c)e)=>Q_net+ q = Q_encl in the gauss Law

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81. S=E*B/mu_0
= 1/(2*pi^2*b)*(s^2)*(t/(b^2-a^2))

What's wrong with this formula guys??

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82. (t*s^2)/(2*(PI^2)*b*(b^2-a^2))

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83. robbo, formula is right, check s^2*t
for example s=24u and t=5u
s^2*t = 24*24*5*1u^3

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84. 10 d) Positive or negative?

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85. Is this correct for 10 d)=

P=1/3T * int(-L*w*(Imax)^2*sin(wt)*cos(wt), 0 , 3T)
Thanks!!!

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86. Jack, and 124, for the formula:(t*s^2)/(2*(PI^2)*b*(b^2-a^2)) = 5.27300181668e-11

at s=12uC/sec, t=1usec, b=0.0053m, a=0.0014m

I've followed the formula, but the answer shows wrong... I hope you guys can help?

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87. Jack, the formula you've used is correct :)

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88. Q11 formulae, anybody??

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89. Jack, yes the formula is OK

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90. 124, I have no idea what on earth I'm doing wrong, followed your formula... and input values and got the same answer everytime I tried, apparently its incorrect! :( Can you input my values and see what answer you get?

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91. robbo,sorry i forgot e_0
(1u*12u^2)/(2*(PI^2)*5.3m*(5.3m^2-1.4m^2)*8.85e-12) =5.95215457341
E =|E|er
|E|=1/(4*pi*e_0*kappa)*q/r^2 for (a<r<b) |E|=1/(4*pi*e_0)*q/r^2 for r>=b

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92. S=E*B/mu_0
= 1/(2*pi^2*b*epsilon_0)*(s^2)*(t/(b^2-a^2))

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93. guys, you can subscribe in the new course ReView (8.MReVx)

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94. 10d)
P=1/3T * int(-L*w*(Imax)^2*sin(wt)*cos(wt), 0 , 3T) = 0!!!!!

T=2*pi*sqrt(L*C)

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95. 124, i think its supposed to be t^2/(b^2-a^2) instead of t to the power of 1.

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96. 9c, 11c anybody?

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97. 11 c) Is the net charge positive or negative?

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98. THIS IS CHEATING!!! YOU ARE NOT FOLLOWING THE HONOUR CODE!!

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99. Dear MIT, you got here by???? Googling for what?

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102. it seems that we cheated. So I leave. Good luck to all!

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