Multiple choice answers (5 Viewers)

[shady145]

No, the angle isn't 90 it is 0. sin0 = 0. Even with your reasoning you're wrong, because torque would have to be a cos curve with your reasoning. torque is not current. With your reasoning, the answer would be A, because B, I and l remain constant.

sorry mate we are wrong... the angle between the side AB is always at 90* to the magnetic field, its only when u do the force on the whole coil that it is a sine curve

 

[cirs]

My multiple choice answers
1 b
2 a
3 c
4 d
5 c
6 a
7 c
8 c
9 a
10 b
11 b
12 d
13 a
14 d
15 a

 

[shady145]

1.C
2.A
3.C
4.D
5.B (I thought too much about it, should be C)
6.A
7.C
8.C
9.A
10.B
11.B
12.D
13.B
14.C
15.A

14/15 dam

hey can u explain question 9 to me... this is my reasoning
right hand push rule, current goes from R to P, the question asks for build up of electrons meaning its in the opposite direction of the current, which gives me a build up at R so i got C

 

[00iCon]

cos@ is the agnle of the coil - 0 degrees at start
sin@ is the angle a wire makes with the magnetic field

 

[Ostentatious]

sorry mate we are wrong... the angle between the side AB is always at 90* to the magnetic field, its only when u do the force on the whole coil that it is a sine curve

Bahaha, yeah I figured it out finally. Thanks jackson!

 

[moke]

the answer to 11 is definetly b. the torque graph cannot be (a) as torque cannot change from positive to negative as this would mean that the motor began turning in the opposite direction. Therefore it can't be (a). It can't be (c) becuase the value of the torque is not constant. It can't be (d) because the force begins as a maximum as the plane of the coil is parallel to the magnetic field. So it has to be (b). And yes (b) is a cos curve as in t=nBIAcostheta. just think of it as the absolute value of the cos curve, such that torque is always positive.

 

[slamduncs]

force is proportional to sintheta... therefore its D

I'm 110% sure its B. Yes it is proportional to sintheta but theta is always 90 degrees to the magnetic field. The FORCE on AB is always constant but swaps every half turn. The torque however is not constant. Therefore B.

 

[Ostentatious]

Bahaha, yeah I figured it out finally. Thanks jackson!

That being said, I still think the answer is A. Anyone care to explain it to me?

 

[kieranjackson91]

B C C C C A C C A B D D A C A

can someone mark me

i choked and i dont wanna do it

ok you asked:
1.Bx
2.Cx
3.C
4.Cx
5.C
6.A
7.C
8.C
9.A
10.B
11.Dx
12.D
13.Ax
14.C
15.A
(assuming i now know the right answers to mark you on)

10/15 so not too bad

 

[Ostentatious]

the answer to 11 is definetly b. the torque graph cannot be (a) as torque cannot change from positive to negative as this would mean that the motor began turning in the opposite direction. Therefore it can't be (a). It can't be (c) becuase the value of the torque is not constant. It can't be (d) because the force begins as a maximum as the plane of the coil is parallel to the magnetic field. So it has to be (b). And yes (b) is a cos curve as in t=nBIAcostheta. just think of it as the absolute value of the cos curve, such that torque is always positive.

Thanks for the explanation

 

[08joel08]

hey can u explain question 9 to me... this is my reasoning
right hand push rule, current goes from R to P, the question asks for build up of electrons meaning its in the opposite direction of the current, which gives me a build up at R so i got C

when u use the right hand push rule for eddy curents, the palm goes in the direction of the force produced, and as the force produced opposes motion it is up in this case, i assume thats where u made ure mistake? or maybe it was the crosses mean into the page thing

i got this question wrong because i read "current" instead of "electrons"

 

[shady145]

when u use the right hand push rule for eddy curents, the palm goes in the direction of the force produced, and as the force produced opposes motion it is up in this case, i assume thats where u made ure mistake? or maybe it was the crosses mean into the page thing

i got this question wrong because i read "current" instead of "electrons"

thats where i went wrong
i thought the force was down because that where its moving =S ahwell

 

[kieranjackson91]

hey can u explain question 9 to me... this is my reasoning
right hand push rule, current goes from R to P, the question asks for build up of electrons meaning its in the opposite direction of the current, which gives me a build up at R so i got C

for question 9, ok field directed into page so fingers into page, direction of conductor down page so thumb points down the page and palm points to right so current is to right. but asks for electrons so electrons go to left therefore P which is A. I hope that helps

 

[Ostentatious]

So is Q9 C (R)?

 

[kieranjackson91]

soz shady i keep trying to correct you when you've already been corrected

 

[untouchablecuz]

ok you asked:
1.Bx
2.Cx
3.C
4.Cx
5.C
6.A
7.C
8.C
9.A
10.B
11.Dx
12.D
13.Ax
14.C
15.A
(assuming i now know the right answers to mark you on)

10/15 so not too bad

if thats the case, im actually quite relieved; i thought it was <7

thanks alot mate

 

[Ostentatious]

Oh boy, so many interpretations, but so far I'm on jackson's side of things xD

 

[00iCon]

1 C
2 A
3 C
4 D
5 C <too easy, at first i thought it was talking about force from solar wind
6 A
7 C
8 C
9 C <right hand palm rule, conventional current goes towards P so electrons go to R
10 B
11 B
12 D
13 B
14 C
15 A
Those are my answers and they're the exact same as the guy behind me :S

Did I really get 15/15?
awesome!

 

[tanuwidge]

11 is D

sin0=0 so force is minimum
as theta increases, force increases it is not constant till 90 degrees
sin90=1 so force is maximum

cos0=1 so initially torque is maximum
cos90=0 so torque is minimum

so its D

QED

 

[Ostentatious]

11 is D

sin0=0 so force is minimum
as theta increases, force increases it is not constant till 90 degrees
sin90=1 so force is maximum

cos0=1 so initially torque is maximum
cos90=0 so torque is minimum

so its D

QED

Nope, carefully look at the direction of the current between A and B.

Draw the direction.

Now draw the direction of the magnetic field lines (N to S)

You'll see they're always perpendicular.