Physics Unit 4 JUNE 11/6/12

[étudiante]

no i don kno i saw it a number of times bt the que is how supernova forms and i wrote tht ans i send u is tht correct? and how did u solve q45 4 the 1st part?

ohkay maybe we're looking at two different questions :S Is the first part abt the luminosity of the sun? :S

 

[étudiante]

Are u talking abt the question in which there is an H-R diagram?

 

[*Sandra*]

ohkay maybe we're looking at two different questions :S Is the first part abt the luminosity of the sun? :S

ya whn they say calculate the initial luminosity

 

[étudiante]

ya whn they say calculate the initial luminosity

Thats using the luminosity equation normally, with the given radius find the area n just substitute
But I cant see any question abt supernova formation there

 

[*Sandra*]

Thats using the luminosity equation normally, with the given radius find the area n just substitute
But I cant see any question abt supernova formation there

is ths 4 the 1st part whn they say its 1.4L ? and supernova is in que 82

 

[étudiante]

is ths 4 the 1st part whn they say its 1.4L ? and supernova is in que 82

Nopes! In the first part u find L then for the second last part, multiply ur answer with 1.6 and use that value as L(sun) and multiply r with 1.06 and use that as r(sun) n substitute u get a new T, use both Ts and find lambda max n just tell them the difference
oh I thought u said it was the same question, gimme a sec pls...

 

[étudiante]

ok thnx alot whn they ask how supernova is formed ? i wrote it ths way as i understood frm the book: During blue supergiant, hydrogen fusion takes place and whn its completed it becmes a red giant. Nuclear fusion of heavier atoms takes place and whn iron is formed there is no more release of energy therefore as the gravity pull becmes significant ths causes the star 2 collapse 2 a high density and explodes forming a supernova is tht correct?

Blue supergiant? I dino we had to know abt those
n yeah its perfect

 

[*Sandra*]

Blue supergiant? I dino we had to know abt those
n yeah its perfect

me neither bt i thnk tht's 4 the old syllabus yest i spend almost my whole day on ths astrophysics after looking at these old ques's and 4 the luminosity 1 i cldn't get it can u jst show me the working plz

 

[étudiante]

me neither bt i thnk tht's 4 the old syllabus yest i spend almost my whole day on ths astrophysics after looking at these old ques's and 4 the luminosity 1 i cldn't get it can u jst show me the working plz

oh maybe To be honest, I haven't seen the syllabus for Astrophysics yet

sure no problem
a) L = (sigma) * T^4 * A
= (5.67 x 10^-8) x (5800^4) x (pi x (7.0 x 10^5)^2) = 9.88 x 10^19 W

b) Surface area = 4(pi)r^2 = x 10^12 m2

c) (same formula as part a)
1.38 x 10^20 = ((5.67 x 10^-8) x T^4 x ( x 10^12) = 6000K
6000 - 5800 = 324 (its not exactly 6000 )

d) Wiens law: (lmbda max)*T = 2.9 x10^-3
first subs T = 5800, then lambda max = 5 x 10^-7
then subs T = 6000, then lambda max = 4.8 x 10^7
Difference = 5.0

PS its not exactly 6000 but a little more, but i cant read the nos I wrote after dat soory

 

[*Sandra*]

oh maybe To be honest, I haven't seen the syllabus for Astrophysics yet

sure no problem
a) L = (sigma) * T^4 * A
= (5.67 x 10^-8) x (5800^4) x (pi x (7.0 x 10^5)^2) = 9.88 x 10^19 W

b) Surface area = 4(pi)r^2 = x 10^12 m2

c) (same formula as part a)
1.38 x 10^20 = ((5.67 x 10^-8) x T^4 x ( x 10^12) = 6000K
6000 - 5800 = 324 (its not exactly 6000 )

d) Wiens law: (lmbda max)*T = 2.9 x10^-3
first subs T = 5800, then lambda max = 5 x 10^-7
then subs T = 6000, then lambda max = 4.8 x 10^7
Difference = 5.0

PS its not exactly 6000 but a little more, but i cant read the nos I wrote after dat soory

its ok bt the 1st ans was 2.8x10^26 W how did they get ths?

 

[étudiante]

its ok bt the 1st ans was 2.8x10^26 W how did they get ths?

Really? I din't check the mark scheme... gimme a sec pls

 

[étudiante]

Oooooooooooooooopsssssssss! My bad *double facepalm*

We have to use L as (3.9 x 10^26)/1.4 because the question says that initially it was less luminous than now by 40%.

Sorry n i HATE these silly mistakes

 

[*Sandra*]

Oooooooooooooooopsssssssss! My bad *double facepalm*

We have to use L as (3.9 x 10^26)/1.4 because the question says that initially it was less luminous than now by 40%.

Sorry n i HATE these silly mistakes

ok y don't we multiply by 1.4? im getting confused in such ques's where calculations r required

 

[étudiante]

ok y don't we multiply by 1.4? im getting confused in such ques's where calculations r required

aawwwhh! Well see they r saying that initially there was less luminosity and the value of L they have given us is the PRESENT one, so we need to divind (cuz we need a smaller number ) dw, this one is likely to catch out many of us -___- Stupid examiners -.-"

 

[*Sandra*]

aawwwhh! Well see they r saying that initially there was less luminosity and the value of L they have given us is the PRESENT one, so we need to divind (cuz we need a smaller number ) dw, this one is likely to catch out many of us -___- Stupid examiners -.-"

ya ur ryt i cnt imagin 6 papers 4 a subject y all ths

 

[étudiante]

ya ur ryt i cnt imagin 6 papers 4 a subject y all ths

EXACTLY n its not like they r MCQ papers like in CIE -.-"

by the way, ne idea how many significant figuires to use for these questions?

 

[*Sandra*]

EXACTLY n its not like they r MCQ papers like in CIE -.-"

by the way, ne idea how many significant figuires to use for these questions?

noo maybe 3 i guess

 

[étudiante]

noo maybe 3 i guess

ohkay... because I see different no of sf used in different places...

btw, do u have the Jan 2012 Examiner's Reports?

 

[*Sandra*]

ohkay... because I see different no of sf used in different places...

btw, do u have the Jan 2012 Examiner's Reports?

ya

 

[étudiante]

ya

Thanksh yewww so much :')