A2 Physics | Post your doubts here

[SkyPilotage]

in that case u know, a varying output will be produced...

like the last one - the orange part...

so peak value is given

ok when it mentions 240 V ac supply./ What is this 240 Volts? r.ms value?

 

[smzimran]

1) ideal gas compressed, means work done on it i.e increases, and they come closer together
Constant temperature means Internal energy is constant, so q must decrease.
2)heating of solid ---> thermal energy input / no expansion no work done.
3)melting of ice, thermal energy required to break bonds, no change in volume against atmosphere/ very small.

R.m.s value for ac current and for ac voltage, is therre a difference in definition.
Is it better to say equivalent to d.c current or do we say it is a steady constant value for current.

Thanks for the first part!


A.c current, in reality, has no consistent or fixed value!
We ASSUME that it has a mean (or average) value, which we call r.m.s value

We assume that the sinosuidal current has a fixed (d.c current like) value equal to r.m.s
I hope you got it!

 

[user]

Definition for r.m.s value of ac : the value of steady / constant voltage that produces same power (in a resistor) as the alternating voltage...(this answer is from mark scheme as far as I remember)

 

[user]

ok when it mentions 240 V ac supply./ What is this 240 Volts? r.ms value?

yup it's the rms value..

 

[SkyPilotage]

Thanks for the first part!


A.c current, in reality, has no consistent or fixed value!
We ASSUME that it has a mean (or average) value, which we call r.m.s value

We assume that the sinosuidal current has a fixed (d.c current like) value equal to r.m.s
I hope you got it!

yup got it, but woe there mean value is different than r.m.s value dont worry i get what you mean
but the problem sometimes, i find that they penalise for writing DC in the definition.

Definition for r.m.s value of ac : the value of steady / constant voltage that produces same power (in a resistor) as the alternating voltage...(this answer is from mark scheme as far as I remember)

Yup thats the best definition there is. My question is if we write DC instead of constant / steady, then why is that incorrect?

By the way , thanks for your help both of you! Jazakum Allah Khairan. Dont know what happened to me there. I suppose its the problem of using different sources at once, which lead to the amplification of the input to lead to a saturated confusion....alright.. now I sound weird.

 

[SkyPilotage]

well for q7 b http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Physics (9702)/9702_w09_qp_41.pdf

can you draw the graphs for the other 2 diodes, not asked for in the question.

 

[user]

You can say that I guess. This is what's in the chris Mee book:
The r.m.s value of the current or voltage is that value of the direct current or voltage that would produce heat at the same rate in a resistor.
Can you please tell me, which mark scheme penalised for saying dc?

 

[smartangel]

http://www.xtremepapers.com/papers/...and AS Level/Physics (9702)/9702_w06_qp_4.pdf Q3 b ii..how do we increase damping?

 

[user]

can you draw the graphs for the other 2 diodes, not asked for in the question.

It'll be only two graphs...
remember..two of them work together, while the other two dont work..?
Check this if you're confused...[feel free to ask if you still have trouble]
Use the +/- buttons to change the direction of the ac input
http://www.flashscience.com/electricity/smoothing.htm

 

[SkyPilotage]

You can say that I guess. This is what's in the chris Mee book:
The r.m.s value of the current or voltage is that value of the direct current or voltage that would produce heat at the same rate in a resistor.
Can you please tell me, which mark scheme penalised for saying dc?

not sure but I may have mis read it, or they may have penalised for writing dc instead of steady. But just to be on the safe side, we write the definition in the mark scheme, which is the steady contant voltage/current....

can you draw the graphs for the other 2 diodes, not asked for in the question.

Can you?

 

[user]

not sure but I may have mis read it, or they may have penalised for writing dc instead of steady. But just to be on the safe side, we write the definition in the mark scheme, which is the steady contant voltage/current....


Can you?

I assume you didnt read my post above...

 

[SkyPilotage]

It'll be only two graphs...
remember..two of them work together, while the other two dont work..?
Check this if you're confused...[feel free to ask if you still have trouble]
Use the +/- buttons to change the direction of the ac input
http://www.flashscience.com/electricity/smoothing.htm

uhmm but when i drew the graphs, i put half wave rectifying on the first diode.
and half wave rectifying on the second diode but with a phase shift of 180 degrees. The mistake i made was not putting it on the negative side.. dont understand why?
and how will the full wave rectifier form at the end.

 

[user]

not sure but I may have mis read it, or they may have penalised for writing dc instead of steady. But just to be on the safe side, we write the definition in the mark scheme, which is the steady contant voltage/current....


Can you?

The blue ones will have the same graph...so do the red ones...that's why i labelled the graphs: first 'set' of diode [let this be the blue one] , and second 'set' of diodes [let this be the red ones]

 

[user]

uhmm but when i drew the graphs, i put half wave rectifying on the first diode.
and half wave rectifying on the second diode but with a phase shift of 180 degrees. The mistake i made was not putting it on the negative side.. dont understand why?
and how will the full wave rectifier form at the end.

Can you see the graph drawn towards the right...? the first produced as the red ones are forward biased...then they become reverse biased and blue ones are forward biased..so the next one produced as in the graph...
Ermm..if still confused, do let me know..

 

[user]

uhmm but when i drew the graphs, i put half wave rectifying on the first diode.
and half wave rectifying on the second diode but with a phase shift of 180 degrees. The mistake i made was not putting it on the negative side.. dont understand why?
and how will the full wave rectifier form at the end.

It'd be one wave form actually what we get...but if we analyze it...we get to know it's combination of two half waves...but overall..a full wave rectifier is what we get..!

 

[SkyPilotage]

Can you see the graph drawn towards the right...? the first produced as the red ones are forward biased...then they become reverse biased and blue ones are forward biased..so the next one produced as in the graph...
Ermm..if still confused, do let me know..

So the ones that hassam drew on page 35 are wrong?
Because that is what is confusing me!

 

[SkyPilotage]

It'd be one wave form actually what we get...but if we analyze it...we get to know it's combination of two half waves...but overall..a full wave rectifier is what we get..!

ok, one more, when the current direction changes, the ac wave has the same shape?
Meaning each half cycle , current direction changes? how is the graph of the current in each half cycle? and how does the diode change it?
I am sorry for all the trouble I'm causing you.

 

[user]

So the ones that hassam drew on page 35 are wrong?
Because that is what is confusing me!

yup...that's wrong as far as I know...! I didn't notice that

This is the correct one:

 

[user]

ok, one more, when the current direction changes, the ac wave has the same direction?

umm...i didnt get what u meant cud u plz elaborate..

 

[SkyPilotage]

umm...i didnt get what u meant cud u plz elaborate..

ok, one more, when the current direction changes, the ac wave has the same shape?
Meaning each half cycle , current direction changes? how is the graph of the current in each half cycle? and how does the diode change it?
I am sorry for all the trouble I'm causing you.