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March 28, 2024, 08:47:35 pm

Author Topic: HSC Physics Question Thread  (Read 1030398 times)  Share 

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jamonwindeyer

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Re: Physics Question Thread
« Reply #1635 on: January 12, 2017, 10:04:37 pm »
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Wow, you and Rui went in hard on this one and its much appreciated. Mb i forgot to think of the little details  in my answer. Your explanation was really good and helped me further understand electromagnetic induction.
Cheers

Awesome! Happy to help ;D

kiwiberry

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Re: Physics Question Thread
« Reply #1636 on: January 14, 2017, 08:40:39 pm »
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Hey,
In a DC motor, is the torque on the coil maximum when the plane of the coil is parallel to the magnetic field?
HSC 2017: English Adv (93) | Maths Ext 1 (99) | Maths Ext 2 (97) | Chemistry (95) | Physics (95)
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bsdfjnlkasn

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Re: Physics Question Thread
« Reply #1637 on: January 14, 2017, 09:16:07 pm »
+1
Hey,
In a DC motor, is the torque on the coil maximum when the plane of the coil is parallel to the magnetic field?

Hey kiwiberry,

You're right and here's why:
Since the expression for torque is: τ=nBIA cos θ we must look at the angle between the magnetic field and the plane of the coil to address cos θ. When they are parallel the angle is 0° and we know that cos0=1 essentially making  τ=nBIA . This would give the maximum value for torque in a DC motor as any angle >0 will result in a smaller τ value.

Hopefully that helped! :)

kiwiberry

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Re: Physics Question Thread
« Reply #1638 on: January 15, 2017, 12:15:16 am »
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Hey kiwiberry,

You're right and here's why:
Since the expression for torque is: τ=nBIA cos θ we must look at the angle between the magnetic field and the plane of the coil to address cos θ. When they are parallel the angle is 0° and we know that cos0=1 essentially making  τ=nBIA . This would give the maximum value for torque in a DC motor as any angle >0 will result in a smaller τ value.

Hopefully that helped! :)

Ah that makes sense, thank you!! :)
HSC 2017: English Adv (93) | Maths Ext 1 (99) | Maths Ext 2 (97) | Chemistry (95) | Physics (95)
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katnisschung

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Re: Physics Question Thread
« Reply #1639 on: January 19, 2017, 02:39:21 pm »
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ok i suppose i could go about memorising the formulas but
idk it helps me when i derive it...
Im trying to derive the length dilation formula and im stuck
(probably becos my algebra skills are terrible and ask me why i took physics...becos i was a fool)

i get that u need to equate the time dilation equation to get length dilation
i just dont understand how the denominator in t2 came to be positive??

becos forward journey= ct1=L_v+vt1    (note v is supposed to be an underscore for L)
t1=(L_v)/(c-v)

return journey =  ct2=L_v+vt2
how did the denominator become c+v??
am i missing sth i don't understand
get me out of here

jamonwindeyer

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Re: Physics Question Thread
« Reply #1640 on: January 19, 2017, 03:18:28 pm »
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ok i suppose i could go about memorising the formulas but
idk it helps me when i derive it...
Im trying to derive the length dilation formula and im stuck
(probably becos my algebra skills are terrible and ask me why i took physics...becos i was a fool)

i get that u need to equate the time dilation equation to get length dilation
i just dont understand how the denominator in t2 came to be positive??

becos forward journey= ct1=L_v+vt1    (note v is supposed to be an underscore for L)
t1=(L_v)/(c-v)

return journey =  ct2=L_v+vt2
how did the denominator become c+v??
am i missing sth i don't understand

Hey Katniss! Purely algebraically you are right, but I think you'll find it has something to do with the direction of \(v\) - Since it is moving in the opposite direction on return, \(v\) will take a new sign. At least, that's my guess - Without seeing the full proof I'm not sure, and this is only something I've seen derived once (and a long time ago too, lol).

Just saying, you are way beyond the scope of the course at this point. I'm a massive fan of deriving formulae, but this is definitely not worth stressing over! Good on you for pushing hard to extend yourself. :)

katnisschung

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Re: Physics Question Thread
« Reply #1641 on: January 19, 2017, 03:25:11 pm »
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thanks Jamon!
oh i see now.... i was racking my brains before trying to figure out why it was pos.

yeah i might stick to memorising the relativity formulae ahha
get me out of here

kiwiberry

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Re: Physics Question Thread
« Reply #1642 on: January 19, 2017, 03:52:07 pm »
+1
ok i suppose i could go about memorising the formulas but
idk it helps me when i derive it...
Im trying to derive the length dilation formula and im stuck
(probably becos my algebra skills are terrible and ask me why i took physics...becos i was a fool)

i get that u need to equate the time dilation equation to get length dilation
i just dont understand how the denominator in t2 came to be positive??

becos forward journey= ct1=L_v+vt1    (note v is supposed to be an underscore for L)
t1=(L_v)/(c-v)

return journey =  ct2=L_v+vt2
how did the denominator become c+v??
am i missing sth i don't understand

Just to elaborate :)
The return journey is supposed to be ct2=L_v-vt2. On the way back, as the train is travelling at velocity v, it will have moved a distance of vt2 in the opposite direction that the light is travelling before the light reaches the end. This means that on the return journey, the light travels a shorter distance than the forward journey to reach the end, this shorter distance being L_v-vt2!
« Last Edit: January 19, 2017, 03:58:42 pm by kiwiberry »
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Rathin

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Re: Physics Question Thread
« Reply #1643 on: January 19, 2017, 05:08:26 pm »
+1
Here are full the time dilation and length contraction derivations if you needed to refer to it. 
« Last Edit: January 19, 2017, 05:11:43 pm by Rathin »
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bholenath125

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Re: Physics Question Thread
« Reply #1644 on: January 20, 2017, 04:58:01 pm »
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I am having significant difficulty in motors and generators in understanding how the motor rotates. Like F= bniCostheta

Is there a site that can explain it better?

jamonwindeyer

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Re: Physics Question Thread
« Reply #1645 on: January 20, 2017, 05:26:17 pm »
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I am having significant difficulty in motors and generators in understanding how the motor rotates. Like F= bniCostheta

Is there a site that can explain it better?

I wrote a little guide on this here which could shed some light!

You should also try looking on Youtube for a video explaining it - A visual picture of how the forces involved produce a rotation can be really beneficial in making it a little clearer ;D try looking up 'HSC How a Motor Works' or something similar ;D

katnisschung

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Re: Physics Question Thread
« Reply #1646 on: January 21, 2017, 04:47:14 pm »
+1
probably not the most appropriate thing to post here
but i get the quickest responses in this thread :)

what topics r u guys planning to cover in the
physics
2u maths
and biology lecture?

i know schools can tend to cover topics in different order
so just wanting a heads up... also really enjoyed the lectures
u guys ran in sept/oct
get me out of here

kiwiberry

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Re: Physics Question Thread
« Reply #1647 on: January 21, 2017, 07:55:47 pm »
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probably not the most appropriate thing to post here
but i get the quickest responses in this thread :)

what topics r u guys planning to cover in the
physics
2u maths
and biology lecture?

i know schools can tend to cover topics in different order
so just wanting a heads up... also really enjoyed the lectures
u guys ran in sept/oct

i would also like to know about the chem and 3u maths lectures :)
HSC 2017: English Adv (93) | Maths Ext 1 (99) | Maths Ext 2 (97) | Chemistry (95) | Physics (95)
ATAR: 99.85

Rathin

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Re: Physics Question Thread
« Reply #1648 on: January 21, 2017, 08:27:33 pm »
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I recommend asking that question to Jamon or Jake's PM as we don't want to derail the physics thread :)
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Aaron12038488

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Re: Physics Question Thread
« Reply #1649 on: January 22, 2017, 10:09:04 am »
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So my parents are deciding to get two tutors for me for Physics. I have started tutoring for 1 of them which is individual tutoring. Is it bad to have two tutors, as they may teach different methods. In the upside is that I have more resources and greater understanding.