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 Ί 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 Ί 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 :)
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 :)
