Can I Use My Calculator for the Upcoming Physics Exam?

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In summary: For question 1, how would you know where the Force is at all?If you want to be absolutely sure about where the force is, you need to use your thumb. If you curl your fingers based on the current or the field, your thumb will tell you where the force is. If it is negative, then you switch.
  • #36
OlderDan said:
That is not the formula you need. That is for finding the field produced by a current in a wire.

The induced emf is the negative of the rate of change of flux through the loop. Flux is related to field strength and area. The field is constant. The area is changing at a constant rate. The current is related to the induced emf and resistance of the loop.
o yaaaaa thanks alot
 
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  • #37
Alt+F4 said:
one more,

http://online.physics.uiuc.edu/cgi/courses/shell/phys102/fall06/prep2a.pl?practice/exam2/sp06

question 24.

i did this like 20 times in other exams, i don't know why it doesn't work here but

F= ILBSintheta = MG

(X)(.1)(.5) = (9.8)(1)
X = 196Amps, but the answer is 98 Amps what gives?
all right so why am i only counting current for one side icne 196/2 = 98
 
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  • #38
Alt+F4 said:
Nope.i get 1.7E-9, 2.2E-8 unless i have to convert it somehow
You are doing something wrong in your calculator. If the current and voltge were in phase you would have a maximum power of 120V*5A=600W. The phase difference reduces this somewhat, but not by a huge amount.
 
  • #39
OlderDan said:
You are doing something wrong in your calculator. If the current and voltge were in phase you would have a maximum power of 120V*5A=600W. The phase difference reduces this somewhat, but not by a huge amount.
hmm well i think there is something wrong with their calculation, i have no idea how they got 25 Degrees to .436 radians, i got .4663 radians so maybe that is why i can't get their answer
 
  • #40
Question 16 please :)
http://online.physics.uiuc.edu/cgi/courses/shell/phys102/fall06/prep2a.pl?practice/exam2/fa05


So i tried doing it on Calculator but since sin180 = 0 i get 0
 
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  • #41
Alt+F4 said:
hmm well i think there is something wrong with their calculation, i have no idea how they got 25 Degrees to .436 radians, i got .4663 radians so maybe that is why i can't get their answer
25/180*π = .43633 not .4663
 
  • #42
OlderDan said:
25/180*π = .43633 not .4663
ya i can't get the answer at all, i tried on diffrent calculators. i am postiive I am typing it correctly
 
  • #43
Alt+F4 said:
ya i can't get the answer at all, i tried on diffrent calculators. i am postiive I am typing it correctly
Are you using the calculator to find the maximum of the product IV? How are you doing this?
 
  • #44
i went to Y = and type in that whole equation, then hit Graph, then did 2nd Graph and found the maximum value
 
  • #45
Alt+F4 said:
http://online.physics.uiuc.edu/cgi/courses/shell/phys102/fall06/prep2a.pl?practice/exam2/fa02

Why is Question 11 C??
is there an explanation for this one or is this one of the thing you memorize
 
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  • #46
Alt+F4 said:
i went to Y = and type in that whole equation, then hit Graph, then did 2nd Graph and found the maximum value
When I do that I get 571.9W using their value of 0.436 for phase in radians, which is correct. What do you get?
 
  • #47
Alt+F4 said:
Question 16 please :)
http://online.physics.uiuc.edu/cgi/courses/shell/phys102/fall06/prep2a.pl?practice/exam2/fa05


So i tried doing it on Calculator but since sin180 = 0 i get 0
It is not sin180. It is sin180t with t constantly changing. You need to find the maximum rate of change of the flux and use the number of turns to find the maximum emf.
 
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  • #48
Alt+F4 said:
http://online.physics.uiuc.edu/cgi/courses/shell/phys102/fall06/prep2a.pl?practice/exam2/fa02

Why is Question 11 C??
Did you find the current in the circuit? Did you compute the voltages for each of the elements from that current?
 
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  • #49
Alt+F4 said:
Last Question of the day i promise :), thanks for everyones help

http://online.physics.uiuc.edu/cgi/courses/shell/phys102/fall06/prep2a.pl?practice/exam2/fa05

Question 3

Why is it just (3)(.7*.2*2) = .084 Why not take into account the left side. Thanks
This is from the left side. It is the only side in the magnetic field. The right side contibutes nothing.
 
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  • #50
OlderDan said:
When I do that I get 571.9W using their value of 0.436 for phase in radians, which is correct. What do you get?
same but the answer is 543 that is why I am so confused
 
  • #51
Alt+F4 said:
one more,

http://online.physics.uiuc.edu/cgi/courses/shell/phys102/fall06/prep2a.pl?practice/exam2/sp06

question 24.

i did this like 20 times in other exams, i don't know why it doesn't work here but

F= ILBSintheta = MG

(X)(.1)(.5) = (9.8)(1)
X = 196Amps, but the answer is 98 Amps what gives?
is this the same idea on how one side isn't really contibuitng?
 
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  • #52
Alt+F4 said:
is this the same idea on how one side isn't really contibuitng?
I thought you had already resolved this one (#24). For this one you only used one side of the loop when you should have used both sides. Both sides contribute to the torque, so only half the current you calculated is needed.
 
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  • #53
OlderDan said:
I thought you had already resolved this one (#24). For this one you only used one side of the loop when you should have used both sides. Both sides contribute to the torqe, so only half the current you calculated is needed.
silly me, thanks a lot for your help like seriously. My TA's arent even that helpful
 
  • #54
Alt+F4 said:
Question 16 please :)
http://online.physics.uiuc.edu/cgi/courses/shell/phys102/fall06/prep2a.pl?practice/exam2/fa05


So i tried doing it on Calculator but since sin180 = 0 i get 0
hmm all right so i graphed this, Does it matter if calc is in radian or degree?
 
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  • #55
http://online.physics.uiuc.edu/cgi/courses/shell/phys102/fall06/prep2a.pl?practice/exam2/su06

Question 20
Finger Curl with current
B Field points Down

I woulda picked Rotates it so that the right side comes out of the page and the left goes in.
 
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  • #56
All right last question until Nov 23rd i think

http://online.physics.uiuc.edu/cgi/courses/shell/phys102/fall06/prep2a.pl?practice/exam2/fa03

Question 21


So W = 2piF = (2*3.14*580*10^3) = 3.6E6
>and 1 / ( sqrt 1*10^-3 * .06*10^-6) = 1.2909 E5

what am i doing wrong
 
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  • #57
Alt+F4 said:
All right last question until Nov 23rd i think

http://online.physics.uiuc.edu/cgi/courses/shell/phys102/fall06/prep2a.pl?practice/exam2/fa03

Question 21


So W = 2piF = (2*3.14*580*10^3) = 3.6E6
>and 1 / ( sqrt 1*10^-3 * .06*10^-6) = 1.2909 E5

what am i doing wrong
You are supposed to be finding the value of C that will make the resonant frequency of the circuit the desired broadcast frequency. How does C affect the net capacitance of the circuit?
 
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  • #58
Alt+F4 said:
http://online.physics.uiuc.edu/cgi/courses/shell/phys102/fall06/prep2a.pl?practice/exam2/su06

Question 20
Finger Curl with current
B Field points Down

I woulda picked Rotates it so that the right side comes out of the page and the left goes in.
Currents parallel to magnetic fields experience no force. Currents at right angles do.
 
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  • #59
Alt+F4 said:
hmm all right so i graphed this, Does it matter if calc is in radian or degree?
Yes. Always use radians for these time dependent problems. If they ask for phase in degrees, convert it from radians. If they give phase in degrees, convert it to radians. Angular frequency is always in radians/sec.
 
  • #60
OlderDan said:
Yes. Always use radians for these time dependent problems. If they ask for phase in degrees, convert it from radians. If they give phase in degrees, convert it to radians. Angular frequency is always in radians/sec.
all right but for some reason when i graph in Radian mode i seriously get like -6 and -5 values unless i am doing something wrong with it
 
  • #61
All right i need a CLarifcation on this one
http://online.physics.uiuc.edu/cgi/courses/shell/phys102/fall06/prep2a.pl?practice/exam2/sp06

Question 21


The angle i pick should be what to the field line? i wanted to do 90-22.5 but that won't work. Thanks alot
 
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  • #62
Last Problem then I am off to exam, Thanks Olderdan and whoever else that helped me. Really appreciate it

http://online.physics.uiuc.edu/cgi/courses/shell/phys102/fall06/prep2a.pl?practice/exam2/fa05


Question 8
 
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  • #63
Alt+F4 said:
All right i need a CLarifcation on this one
http://online.physics.uiuc.edu/cgi/courses/shell/phys102/fall06/prep2a.pl?practice/exam2/sp06

Question 21


The angle i pick should be what to the field line? i wanted to do 90-22.5 but that won't work. Thanks alot
Rotate through the small angle from the direction of v to the direction of B. It is just 22.5
 
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  • #64
Alt+F4 said:
Last Problem then I am off to exam, Thanks Olderdan and whoever else that helped me. Really appreciate it

http://online.physics.uiuc.edu/cgi/courses/shell/phys102/fall06/prep2a.pl?practice/exam2/fa05


Question 8
Flux is
Φ = BAcosθ where θ is the angle between the loop normal and B. θ = 30 degrees

The only thing changing is B, so

dΦ/dt = (Acosθ)dB/dt
 
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  • #65
Can't you take the exam for me?
 
  • #66
Alt+F4 said:
Can't you take the exam for me?
What exam are you taking? Could I bring all my reference materials with me? I still remember how to do this stuff, but it sure is nice having the references readily available when you don't remember the exact formulas, values of constants, etc.
 
  • #67
OlderDan said:
What exam are you taking? Could I bring all my reference materials with me? I still remember how to do this stuff, but it sure is nice having the references readily available when you don't remember the exact formulas, values of constants, etc.
nope no refrence but u could program ur calculator. I am takin physics exam in like 2 hrs.
 

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