A2 Physics | Post your doubts here

[hm12]

my problem is only in the second interval..
graph is actually like this:

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but my answer:​

my answer..the solid line..​

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why so, is what i'm confused abt..​

the teacher who solved this red spot is my physics teacher while teaching us he said that both the curves are acceptable the one you drew in the second interval will also be acceptable

 

[user]

the teacher who solved this red spot is my physics teacher while teaching us he said that both the curves are acceptable the one you drew in the second interval will also be acceptable

that's a relief

 

[angelicsuccubus]

A resistance thermometer and a thermocouple thermometer are both used at the same
time to measure the temperature of a water bath.

Explain why, although both thermometers have been calibrated correctly and are at
equilibrium, they may record different temperatures. (2)

 

[Aahliya]

Anyone who can explain why Force is equal to zero in 6)b (ii)
M/J 2008 P42
A small rectangular coil ABCD contains 140 turns of wire. The sides AB and BC of the coil
are of lengths 4.5 cm and 2.8 cm respectively, as shown in Fig. 6.1.
The coil is held between the poles of a large magnet so that the coil can rotate about an axis
through its centre.
The magnet produces a uniform magnetic field of flux density B between its poles.
When the current in the coil is 170 mA, the maximum torque produced in the coil is
2.1 × 10–3 N m.

(b) For the coil in the position shown in Fig. 6.1, calculate the magnitude of the force on
(i) side AB of the coil,
(ii) side BC of the coil.

 

[SkyPilotage]

the teacher who solved this red spot is my physics teacher while teaching us he said that both the curves are acceptable the one you drew in the second interval will also be acceptable

that's a relief

Although I had the same answer, I do not think it is acceptable, check my post to smzimran.

 

[angelicsuccubus]

but this thing doesnt apply in maths atleast...and even in physics there are questions in which they use the exact values :/

yeh and with experience you should know.. when to round off and when not to... when the value is funky on your calculator, and is meant to be an answer? round off for the next part, kay?

 

[smzimran]

I know the answer drawn is correct but
Let me comment on something,
1-How do you know if the rate of decrease is decreasing or constant or increasing? -Please note that emf is the Numerical value of the rate of change of flux, so in both graphs the rate of change of flux is decreasing. But what I dont get is how to know whether the rate of decrease is decreasing or constant or increasing?
2-When you have alternating current , why isnt the graph of the induced emf same like the one drawn in this question?

I think there are 2 mistakes in that graph,
-First thing, the emf induced in the last part should not be greater than the first part.
-Second thing, at the very beginning the gradient is 99% vertical, so I think the emf induced at that point is almost at infinity, hence a line should not be connecting the x-axis to the graph.
[ This is one of the reasons I believe the second graph is wrong ]
Another reason is that the gradient of the current tends to become zero slightly before the end mark, so the emf graph should touch the x-axis.

The induced emf is proportional to the rate of cutting of flux means it is the differentiation of the primary voltage or current, how can the graphs be same ???

The emf induced in last part is greater because slope of decrease of current is greater, means in small time, more flux is cut by the great amount of charge moving in small time so the rate of change of flux is greater and thus, the induced emf (which is proportional to rate of change of flux) is greater!

The initial gradient is not 99% vertical if it was, the shape would never be in the form of the graph that it is! It should have been a vertical line at start up which it is not! Have you not studied this shape of the graph in detail before?

It is touching the x-axis! The e.m.f in the third part is a sudden increase without any interval!

I hope that clears the doubts!

 

[SkyPilotage]

The induced emf is proportional to the rate of cutting of flux means it is the differentiation of the primary voltage or current, how can the graphs be same ???

The emf induced in last part is greater because slope of decrease of current is greater, means in small time, more flux is cut by the great amount of charge moving in small time so the rate of change of flux is greater and thus, the induced emf (which is proportional to rate of change of flux) is greater!

The initial gradient is not 99% vertical if it was, the shape would never be in the form of the graph that it is! It should have been a vertical line at start up which it is not! Have you not studied this shape of the graph in detail before?

It is touching the x-axis! The e.m.f in the third part is a sudden increase without any interval!

I hope that clears the doubts!

ehh, im not saying that graph is wrong, im asking question {not been addressed }
The decreasing gradient of the current, look at the y-values of the emf.
If the y values of emf is decreasing, then the gradient of current is decreasing.
However, the RATE of the DECREASE of the gradient will trace the shape of the induced emf. I dont know how to know.
THe only way I can know the shape of the curve, is that gradient is max in beginning so induced emf at beginning is infinity. and that at the graph of emf touches the x-axis.

 

[smzimran]

ehh, im not saying that graph is wrong, im asking question {not been addressed }
The decreasing gradient of the current, look at the y-values of the emf.
If the y values of emf is decreasing, then the gradient of current is decreasing.
However, the RATE of the DECREASE of the gradient will trace the shape of the induced emf. I dont know how to know.
THe only way I can know the shape of the curve, is that gradient is max in beginning so induced emf at beginning is infinity. and that at the graph of emf touches the x-axis.

I dont clearly get your doubt and Im sorry brother but can't explain it in a better way!

 

[smartangel]

please tell me the definition for Linear absorption coefficient. its a 3 mark question in the past papers and i cant find a suitable explanation for it. if anyone could help me out please?

 

[hassam]

please tell me the definition for Linear absorption coefficient. its a 3 mark question in the past papers and i cant find a suitable explanation for it. if anyone could help me out please?

for a parallel beam incident on a material linear absorption coefficient is the value of mu in the expression Io *e^-ux

 

[user]

please tell me the definition for Linear absorption coefficient. its a 3 mark question in the past papers and i cant find a suitable explanation for it. if anyone could help me out please?

 

[angelgirl:)]

m/j 2008 Q5b...this kind of questions i can never solve ...is there any1 to help me out and tell me the method how to do it??

 

[user]

ehh, im not saying that graph is wrong, im asking question {not been addressed }
The decreasing gradient of the current, look at the y-values of the emf.
If the y values of emf is decreasing, then the gradient of current is decreasing.
However, the RATE of the DECREASE of the gradient will trace the shape of the induced emf. I dont know how to know.
THe only way I can know the shape of the curve, is that gradient is max in beginning so induced emf at beginning is infinity. and that at the graph of emf touches the x-axis.

i think we better leave this...and keep this in our mind..
move on and prepare for the rest

 

[angelicsuccubus]

Explain this "electron flow to the right is equivalent to current flow to the left"

 

[smzimran]

I dont clearly get your doubt and Im sorry brother but can't explain it in a better way!

i think we better leave this...and keep this in our mind..
move on and prepare for the rest

I agree with 'user'
There's no time left now!

 

[user]

I agree with 'user'
There's no time left now!

and btw thanks a lot for your time..
jazakAllah khairen..
may Allah help you and us all..to acheive more than we deserve...aameen!

 

[waleedsmz]

I dont clearly get your doubt and Im sorry brother but can't explain it in a better way!

I agree with what sky is saying... I think he means that the gradient of the curve is the E.M.F. and the gradient is decreasing so the value on the Y-axis on the emf is decreasing. However, we don't know the rate of decrease. In other words, we don't know the gradient of the e.m.f. ( The gradient of the gradient of the original curve ).

Anyways, I believe it doesn't matter as long as it has a decreasing value... It has one mark anyways as far as I remember...

please tell me the definition for Linear absorption coefficient. its a 3 mark question in the past papers and i cant find a suitable explanation for it. if anyone could help me out please?

I honestly don't know a definition but I simply write the equation: I=I0e^(ux)
And identify each of the symbols:
I is the emergent intensity
I0 is the initial intensity
x is the distance traveled by the beam

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If anyone wants to ask a question please link both the paper and the mark scheme to the exam. We don't have much time and I'm sure it's more convenient that way.​

 

[smzimran]

Explain this "electron flow to the right is equivalent to current flow to the left"

Conventional current is the opposite to electron current!
Conventional current is in the direction of flow of protons while electron current is in the direction of flow of electrons!
Unless mentioned, the term 'current' means conventional current.

 

[angelgirl:)]

Explain this "electron flow to the right is equivalent to current flow to the left"

current flow is the conventional flow of e-...its the flow of e- only but the direction is taken to opposite the movment of e-...so dats y e- flow to the right is equavalent to the current flow to the left...
this is wat i learnt in my Olevel...but i dont no how far my answer is true...