Help with H2 Physics A-Level qualitative questions
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I have a few answer keys with me, but they're contradicting so I honestly don't know what to trust. Would like to hear some of your opinions please thanks :)
2013 P3 Q4(b)(ii)
Use Faraday's law to explain whether the output and the input potential differences are in phase. [3]
it's an ideal transformer, btw. One answer key says it's in phase, another says it's out of phase.
2012 P3 Q7(a)(iii)
Suggest why, when defining electric field strength, the test particle must be stationary. [1]
One of my answer key says it's because moving charges produce electromagnetic waves which are perpendicular electric and magnetic fields and hence will distort the original field in the region. but I googled and it is actually accelerating not moving? and is this in the syllabus? The other one, the one done by my school, I feel that it doesn't even answer the question.
Please help if you have some insightful opinion. Thank you :)
oh. I also have this thing I don't understand. Can anyone help explain to me please? :D
2011 P3 Q8(c)(i)
Diagram shows a battery with e.m.f. 12.0 V and negligible internal resistance. A resistor of resistance 3.0 Ω is permanently connected to one of its terminals.
The battery and resistor form a power supply with terminals X and Y. A variable resistor of resistance R is connected across terminals X and Y.Calculate
1. the maximum possible current from the supply.
answer is 4.0 obviously
2. the minimum safe power rating of the 3.0 Ω resistor.
this is the part I don't get. Answer is 48 W, because Pmin = I^2 r. But why is the MINIMUM power based on MAXIMUM current? I don't even understand why is there even a minimum power in the first place? Meaning power supplied to the resistor cannot go below it? but isn't it weird, shouldn't it be maximum instead, cos I thought resistors are only unable to withstand power that is too high, but what's wrong with it being too low?Thanks a lot :)
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Im not a physics student, so I can't help you with this. But I am a student taking my Alevels so I suggest that instead of waiting for not so reliable answers on this page, please go consult your tutors. I know they are down for invigilation so you can't book consultations but you can always whatsapp them and wait for their reply. Or you can also consult the h2 physics tutors that are still in sch such as the j1 teachers. Just cause they teach j1 doesn't mean they dk the j2 syllabus. It's always best to clarify with teachers.
All the best for your papers! 😊💪💪
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Originally posted by Ilovedonutsxd:
Im not a physics student, so I can't help you with this. But I am a student taking my Alevels so I suggest that instead of waiting for not so reliable answers on this page, please go consult your tutors. I know they are down for invigilation so you can't book consultations but you can always whatsapp them and wait for their reply. Or you can also consult the h2 physics tutors that are still in sch such as the j1 teachers. Just cause they teach j1 doesn't mean they dk the j2 syllabus. It's always best to clarify with teachers.
All the best for your papers! 😊💪💪
haha hey fellow J2 xD lol if you only knew how busy (read: lazy) my teacher is. tried asking for consultations to no avail, everytime I wanted to ask him questions after class he would just run away. He didn't give us his number either cos he doesn't wanna be bothered. though I have his number cos I'm the Physics rep, I feel bad whatsapping him too. he gives tuition you see, and he doesn't care about his school students. but anw nvm lol I just wanna get more opinions cause it's not like the answers I have with me are not written by Physics teachers. problem is no one really knows what Cambridge wants so yeahh. anw thanks and all the best for you too! :))
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If H2 Physics advice given on this page is posted by Eagle, rest assured it's reliable (even more reliable than most school teachers).
If H2 Math advice given on this page is posted by WeeWS or Eagle, rest assured it's reliable (even more reliable than most school teachers).
If H2 Chemistry advice given on this page is posted by UltimaOnline, rest assured it's reliable (even more reliable than most school teachers).
But of course that's only if Eagle or WeeWS are present to reply you on this forum. -
2011 P3 Q8(c)(i)
Diagram shows a battery with e.m.f. 12.0 V and negligible internal resistance. A resistor of resistance 3.0 Ω is permanently connected to one of its terminals.
The battery and resistor form a power supply with terminals X and Y. A variable resistor of resistance R is connected across terminals X and Y.---------------
They are asking for the minimum SAFE power level rating. So in a sense, they are trying to trying to find the least power rating that is needed to stop the largest possible value of the current.
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Originally posted by UltimaOnline:
If H2 Physics advice given on this page is posted by Eagle, rest assured it's reliable (even more reliable than most school teachers).
If H2 Math advice given on this page is posted by WeeWS or Eagle, rest assured it's reliable (even more reliable than most school teachers).
If H2 Chemistry advice given on this page is posted by UltimaOnline, rest assured it's reliable (even more reliable than most school teachers).
But of course that's only if Eagle or WeeWS are present to reply you on this forum.thank you for bothering to take the time to help us! :)
Originally posted by qdtimes2:2011 P3 Q8(c)(i)
Diagram shows a battery with e.m.f. 12.0 V and negligible internal resistance. A resistor of resistance 3.0 Ω is permanently connected to one of its terminals.
The battery and resistor form a power supply with terminals X and Y. A variable resistor of resistance R is connected across terminals X and Y.---------------
They are asking for the minimum SAFE power level rating. So in a sense, they are trying to trying to find the least power rating that is needed to stop the largest possible value of the current.
oh.. umm, I think I understood safe power rating wrongly lol. can I just clarify.. "least power rating that is needed to stop the largest possible value of the current" but what stops current is the resistance right..? so the minimum safe power rating is like the minimum resistance needed? so the power rating actually indicates the resistance..? correct me if I'm wrong please thanks! :)
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sorry that my phrasing is so confusing.
yeah, power rating itself doesn't resist or stop the electric current.
From my understanding, the minimum safe power rating is an indication, in the form of power W, which shows that the 3 Ohms resistor will continue to work properly in 4A current. Let's say if a battery produces a "power" exceeding that rating in that resistor, the resistor could possibly malfunction through melting etc.
Rephrasing it would be: " Find the least power rating needed to accustom to the largest possible value of the electric current"
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Originally posted by qdtimes2:
sorry that my phrasing is so confusing.
yeah, power rating itself doesn't resist or stop the electric current.
From my understanding, the minimum safe power rating is an indication, in the form of power W, which shows that the 3 Ohms resistor will continue to work properly in 4A current. Let's say if a battery produces a "power" exceeding that rating in that resistor, the resistor could possibly malfunction through melting etc.
Rephrasing it would be: " Find the least power rating needed to accustom to the largest possible value of the electric current"
omg, I'm confused D; wait. um, when you said "the 3 Ohms resistor will continue to work properly in 4A current", does it mean it won't work when current is >4A or <4A??
and if like you said the resistor could possibly malfunction if the power exceeds that rating, then wouldn't that be maximum power that it can take? then why is the safe power rating a minimum?
uh I'm sorry for asking so much but I can't seem to understand this ><
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hah...looks like we are both brain-fried eh..hope this clears things up
Safe
Power rating = 48 W ; Current ≤ 4A
Not Safe
Power rating = 48 W; Current > 4A
or Current = 4A, Power produced = 48 W ; but e.g. Power rating = 1 W only
Qn: if Current ≤ 4A,
A safe power rating must be anywhere ≥ 48 W
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Originally posted by qdtimes2:
hah...looks like we are both brain-fried eh..hope this clears things up
Safe
Power rating = 48 W ; Current ≤ 4A
Not Safe
Power rating = 48 W; Current vtk vd> 4A
or Current = 4A, Power produced = 48 W ; but e.g. Power rating = 1 W only
Qn: if Current ≤ 4A,
A safe power rating must be anywhere ≥ 48 W
Ohhh! I think I get itt haha
So the minimum is for the rating and not the power is it? As in, doesn't mean if power supplied to the resistor is <48W the resistor will malfunction right? It's just that for a power rating, it makes sense for it to not be less than 48W since it hasn't even corresponded to the maximum current..?
ok if I'm not making sense it's ok but I think I get it alr haha thankss anyway :)
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I have a few answer keys with me, but they're contradicting so I honestly don't know what to trust. Would like to hear some of your opinions please thanks :)
2013 P3 Q4(b)(ii)
Use Faraday's law to explain whether the output and the input potential differences are in phase. [3]
it's an ideal transformer, btw. One answer key says it's in phase, another says it's out of phase.
They are out of phase by 90 degree as emf induced in the secondary coils is the rate of change of magnetic flux linkage. it shifted the sinusoidal input p.d by 90 degree or pi/2 radian.
2012 P3 Q7(a)(iii)
Suggest why, when defining electric field strength, the test particle must be stationary. [1]
One of my answer key says it's because moving charges produce electromagnetic waves which are perpendicular electric and magnetic fields and hence will distort the original field in the region. but I googled and it is actually accelerating not moving? and is this in the syllabus? The other one, the one done by my school, I feel that it doesn't even answer the question.
Please help if you have some insightful opinion. Thank you :)
oh. I also have this thing I don't understand. Can anyone help explain to me please? :D
Charge particles that accelerate will produce EM wave, we learned this in the X-ray production section. In any definition, we always try to not have any ambiguity. Therefore, to avoid having EM waves that could be produced from the test charge . we want to define E-field to have the test charge being stantionary.
2011 P3 Q8(c)(i)
Diagram shows a battery with e.m.f. 12.0 V and negligible internal resistance. A resistor of resistance 3.0 Ω is permanently connected to one of its terminals.
The battery and resistor form a power supply with terminals X and Y. A variable resistor of resistance R is connected across terminals X and Y.Calculate
1. the maximum possible current from the supply.
answer is 4.0 obviously
2. the minimum safe power rating of the 3.0 Ω resistor.
this is the part I don't get. Answer is 48 W, because Pmin = I^2 r. But why is the MINIMUM power based on MAXIMUM current? I don't even understand why is there even a minimum power in the first place? Meaning power supplied to the resistor cannot go below it? but isn't it weird, shouldn't it be maximum instead, cos I thought resistors are only unable to withstand power that is too high, but what's wrong with it being too low?Part 2 of question is right to ask for Minimum safety power rating.
Since the largest Power dissipation for the 3 ohm resistor is calculated to be 48W. the Minimum safety power rating for the resistor should be more than 48W so that any users know that the power dissipation could be as large as 48W.
Thanks
My comments in red. Many answers by books are provided by not credible personal. Their answers are not reliable. I have taught tuitions for many years for A level physics and always told students to just use the answer keys as a reference. if in doubt, always go back to their school teacher or a trained tutor. if you need further help, do PM me
-
Originally posted by UltimaOnline:
If H2 Physics advice given on this page is posted by Eagle, rest assured it's reliable (even more reliable than most school teachers).
If H2 Math advice given on this page is posted by WeeWS or Eagle, rest assured it's reliable (even more reliable than most school teachers).
If H2 Chemistry advice given on this page is posted by UltimaOnline, rest assured it's reliable (even more reliable than most school teachers).
But of course that's only if Eagle or WeeWS are present to reply you on this forum.Thanks :)
Was too busy preparing my current students for their O and A Level physics. Wasn't on forum for quite a while. My personal record of graduating students, trying to break it every year.
Guess it's too late to answer now that A level Physics paper 3 is over.
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Added my comments in Blue
I have a few answer keys with me, but they're contradicting so I honestly don't know what to trust. Would like to hear some of your opinions please thanks :)
2013 P3 Q4(b)(ii)
Use Faraday's law to explain whether the output and the input potential differences are in phase. [3]
it's an ideal transformer, btw. One answer key says it's in phase, another says it's out of phase.
They are out of phase by 90 degree as emf induced in the secondary coils is the rate of change of magnetic flux linkage. it shifted the sinusoidal input p.d by 90 degree or pi/2 radian.
The TYS answer that mentioned in phase was with reference to inductors, which is something out of A Level syllabus. Out of phase by 90 degrees because the rate of change of sine is cosine.
2012 P3 Q7(a)(iii)
Suggest why, when defining electric field strength, the test particle must be stationary. [1]
One of my answer key says it's because moving charges produce electromagnetic waves which are perpendicular electric and magnetic fields and hence will distort the original field in the region. but I googled and it is actually accelerating not moving? and is this in the syllabus? The other one, the one done by my school, I feel that it doesn't even answer the question.
Please help if you have some insightful opinion. Thank you :)
oh. I also have this thing I don't understand. Can anyone help explain to me please? :D
Charge particles that accelerate will produce EM wave, we learned this in the X-ray production section. In any definition, we always try to not have any ambiguity. Therefore, to avoid having EM waves that could be produced from the test charge . we want to define E-field to have the test charge being stantionary.
The definition of a E-field strength is force per unit charge on a stationary test charge.
So my thoughts are, if the charge is moving, it may be affected by the magnetic fields because a moving charge may experience forces due to magnetic fields. So any force experienced my a moving test charge may not be solely due to the E-field anymore.
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Originally posted by Mcdgdgd100:
I have a few answer keys with me, but they're contradicting so I honestly don't know what to trust. Would like to hear some of your opinions please thanks :)
2013 P3 Q4(b)(ii)
Use Faraday's law to explain whether the output and the input potential differences are in phase. [3]
it's an ideal transformer, btw. One answer key says it's in phase, another says it's out of phase.
They are out of phase by 90 degree as emf induced in the secondary coils is the rate of change of magnetic flux linkage. it shifted the sinusoidal input p.d by 90 degree or pi/2 radian.
2012 P3 Q7(a)(iii)
Suggest why, when defining electric field strength, the test particle must be stationary. [1]
One of my answer key says it's because moving charges produce electromagnetic waves which are perpendicular electric and magnetic fields and hence will distort the original field in the region. but I googled and it is actually accelerating not moving? and is this in the syllabus? The other one, the one done by my school, I feel that it doesn't even answer the question.
Please help if you have some insightful opinion. Thank you :)
oh. I also have this thing I don't understand. Can anyone help explain to me please? :D
Charge particles that accelerate will produce EM wave, we learned this in the X-ray production section. In any definition, we always try to not have any ambiguity. Therefore, to avoid having EM waves that could be produced from the test charge . we want to define E-field to have the test charge being stantionary.
2011 P3 Q8(c)(i)
Diagram shows a battery with e.m.f. 12.0 V and negligible internal resistance. A resistor of resistance 3.0 Ω is permanently connected to one of its terminals.
The battery and resistor form a power supply with terminals X and Y. A variable resistor of resistance R is connected across terminals X and Y.Calculate
1. the maximum possible current from the supply.
answer is 4.0 obviously
2. the minimum safe power rating of the 3.0 Ω resistor.
this is the part I don't get. Answer is 48 W, because Pmin = I^2 r. But why is the MINIMUM power based on MAXIMUM current? I don't even understand why is there even a minimum power in the first place? Meaning power supplied to the resistor cannot go below it? but isn't it weird, shouldn't it be maximum instead, cos I thought resistors are only unable to withstand power that is too high, but what's wrong with it being too low?Part 2 of question is right to ask for Minimum safety power rating.
Since the largest Power dissipation for the 3 ohm resistor is calculated to be 48W. the Minimum safety power rating for the resistor should be more than 48W so that any users know that the power dissipation could be as large as 48W.
Thanks
My comments in red. Many answers by books are provided by not credible personal. Their answers are not reliable. I have taught tuitions for many years for A level physics and always told students to just use the answer keys as a reference. if in doubt, always go back to their school teacher or a trained tutor. if you need further help, do PM me
thanks for the answers! :) yep now I get it for the minimum power haha thanks :) oh but can I clarify for the thing you said charged particles that accelerate will produce EM waves as learnt in the x-ray production. but for x-ray production it's because the accelerated electrons hit the tungsten metal and the energy is converted to EM waves right? but will charged particles accelerating themselves (without interaction with any other matter) produce EM waves? haha just curious. and thanks :)
Originally posted by eagle:Added my comments in Blue
I have a few answer keys with me, but they're contradicting so I honestly don't know what to trust. Would like to hear some of your opinions please thanks :)
2013 P3 Q4(b)(ii)
Use Faraday's law to explain whether the output and the input potential differences are in phase. [3]
it's an ideal transformer, btw. One answer key says it's in phase, another says it's out of phase.
They are out of phase by 90 degree as emf induced in the secondary coils is the rate of change of magnetic flux linkage. it shifted the sinusoidal input p.d by 90 degree or pi/2 radian.
The TYS answer that mentioned in phase was with reference to inductors, which is something out of A Level syllabus. Out of phase by 90 degrees because the rate of change of sine is cosine.
2012 P3 Q7(a)(iii)
Suggest why, when defining electric field strength, the test particle must be stationary. [1]
One of my answer key says it's because moving charges produce electromagnetic waves which are perpendicular electric and magnetic fields and hence will distort the original field in the region. but I googled and it is actually accelerating not moving? and is this in the syllabus? The other one, the one done by my school, I feel that it doesn't even answer the question.
Please help if you have some insightful opinion. Thank you :)
oh. I also have this thing I don't understand. Can anyone help explain to me please? :D
Charge particles that accelerate will produce EM wave, we learned this in the X-ray production section. In any definition, we always try to not have any ambiguity. Therefore, to avoid having EM waves that could be produced from the test charge . we want to define E-field to have the test charge being stantionary.
The definition of a E-field strength is force per unit charge on a stationary test charge.
So my thoughts are, if the charge is moving, it may be affected by the magnetic fields because a moving charge may experience forces due to magnetic fields. So any force experienced my a moving test charge may not be solely due to the E-field anymore.
thank you for the answers! :) and it's ok haha I asked not only for A Level preparation but I also wanna know. lifelong learning haha thanks anyway :)