***2015 LC Physics - June 15th***

Chocolalla

Cr4pSnip3r wrote: »

Looking for a C3/C2 with how that went. Tbh, that'd be fine with me. Looking for 400 points overall and if I don't fail maths then it should get to about that.

Same just need around 420 and I'll be happy 👌👌

otoolej2

Seannyyboy wrote: »

What are standing waves and how do they occur?

I was'ent exactly sure what they were, but they are formed when two waves travelling in opposite directions with the same frequency and amplitude , meet and combine.

I think i just threw in that there are periodic waves for the "what are they part"

What did people say for the advantages of kelvin as a S.I unit? odd question.

Chickennuggets

Benm123 wrote: »

Hmm.. This is confusing me.
I did
E=Mc^2
Taking m as mass of electron
And c as speed of light
Then put my value for over eV.

I got 510.99 MeV then which rounded to a nice 511, which seemed like a more suitable answer than them asking for mega electron volts and then having a 0.something answer.
But I'm doubting myself now that others have said they also got 0.something MeV

Also, coming out of the exam my friend who usually gets A1's said he got 0.something but then I asked did he square the speed of light and he said ohhhh **** no he didn't.
What did anyone else get?

M = mass of neutron minus the mass of the proton and electron ?

otoolej2

Chickennuggets wrote: »

M = mass of neutron minus the mass of the proton and electron ?

and minus the mass of the neutrino i think?

The_N4sir

I think^^^ is where I went wrong

Lc2015acc

Chocolalla wrote: »

I just gave the def for magnetic flux, u?

The tesla is the SI unit of magnetic flux density. It was in one of the paragraphs of the text I think

Chickennuggets

otoolej2 wrote: »

and minus the mass of the neutrino i think?

Yea , I couldnt find that in the log tables !!

Hon the Dubs

otoolej2 wrote: »

and minus the mass of the neutrino i think?

I thought mass of the neutrino is so small that it's disregarded no?

AMDD

Seannyyboy wrote: »

What are standing waves and how do they occur?

When 2 waves of the same frequency and amplitude meet they produce a stationary/standing wave. This was the definition I was given for Stationary waves so wasn't too sure on how to answer both parts.

smartz

Benm123 wrote: »

Hmm.. This is confusing me.
I did
E=Mc^2
Taking m as mass of electron
And c as speed of light
Then put my value for over eV.

I got 510.99 MeV then which rounded to a nice 511, which seemed like a more suitable answer than them asking for mega electron volts and then having a 0.something answer.
But I'm doubting myself now that others have said they also got 0.something MeV

Also, coming out of the exam my friend who usually gets A1's said he got 0.something but then I asked did he square the speed of light and he said ohhhh **** no he didn't.
What did anyone else get?

Just did that calculation out again and I got 0.611 MeV, that's without including the mass of the neutrino (because it's so small as to be negligible).

Broseph

Jammysticks wrote: »

Does anybody know what the circuit diagram for the Q4 expt was?

I said that diagram was the one with the power pack, voltmeter, ammeter, filament bulb and the potentiometer. I think potentiometer is right not 100% sure.

Chickennuggets

What did people get for q5 , the would about sun shinning on pitch

Broseph

Chickennuggets wrote: »

What did people get for q5 , the would about sun shinning on pitch

Cant remember but I got the area of the pitch, multiplied it by the solar constant and multiplied that by 90 minutes (in seconds).

Seannyyboy

For the question on the energy from beta decay the answer is 0.78 mega electron volts (you can just Google it to find the answer) but if you use the mass values of the proton / neutron etc from page 48 of the log tables (ie. Masses relative to mass of electron) , you will get an answer of 1.022MeV (which if what i did!)
I just hope i get the marks for it, I mean it's in the log tables like!

Fiona G

smartz wrote:

Just did that calculation out again and I got 0.611 MeV, that's without including the mass of the neutrino (because it's so small as to be negligible).

I don't think the mass of a neutrino is negligible. Sure the whole reason they were postulated was because their mass was needed for the equation to work :P

You get the mass of it by multiplying its relative mass by the mass of the electron. Both values in the tables

DarraghF197

Were we meant to put down the numbers to the decimal places given in the log tables? Spent ages writing down (3.10963296)(2.9979702437)*2....

I was about to write my answers on my exam paper at the end but didn't bother. Kind of annoyed, now that I'm wrecked from Accounting!

Anyways, very nice paper. Could do seven Section B questions fully, so I did six. All went very well, was delighted with Q5. Section A was a bit worse for me. I'd nearly forgotten how to do Boyles law and messed up my calculation for Monochromatic light.

Overall, very happy with that! Expecting a very comfortable A1

smartz

Fiona G wrote: »

I don't think the mass of a neutrino is negligible. Sure the whole reason they were postulated was because their mass was needed for the equation to work :P

You get the mass of it by multiplying its relative mass by the mass of the electron. Both values in the tables

I just did it out another time and still got .611 MeV, this time including the mass of the neutrino. I think the mass is negligible because it's something *10^-31 x 10^-6.

Fiona G

smartz wrote:

I just did it out another time and still got .611 MeV, this time including the mass of the neutrino. I think the mass is negligible because it's something *10^-31 x 10^-6.

Oh okay, never mind! Apologies

otoolej2

Seannyyboy wrote: »

For the question on the energy from beta decay the answer is 0.78 mega electron volts (you can just Google it to find the answer) but if you use the mass values of the proton / neutron etc from page 48 of the log tables (ie. Masses relative to mass of electron) , you will get an answer of 1.022MeV (which if what i did!)
I just hope i get the marks for it, I mean it's in the log tables like!

ye that was my answer also, why do you think its wrong?

Broseph

Was the question 4 diagram drawn with a potentiometer?

Benm123

smartz wrote: »

Just did that calculation out again and I got 0.611 MeV, that's without including the mass of the neutrino (because it's so small as to be negligible).

Just realised that I gave the wrong equation for beta decay which then lead me to using the wrong masses for the calculation...
On top of that I then got 511 eV which for some reason in the exam I perceived to be mega electron volts, i.e without changing it to mega myself...

So I'm suddenly gone from expecting a solid B1 to now doubting myself completely...
Should not have come onto this forum lol

Broseph

Benm123 wrote: »

Just realised that I gave the wrong equation for beta decay which then lead me to using the wrong masses for the calculation...
On top of that I then got 511 eV which for some reason, in the exam I perceived to be mega electron volts, i.e without changing it to mega myself...

So I'm suddenly gone from expecting a solid B1 to know doubting myself completely...
Should not have come onto this forum lol

That's a maximum of 9 marks lost and you get marks for attempting to find the MeV aswel so at worst it's about a 3/9 which is only 6 marks!!

Has anyone got a marking scheme?

Seannyyboy

otoolej2 wrote: »

ye that was my answer also, why do you think its wrong?

Because if you use the values of the masses relative to the electron, you get 1.022 instead of 0.78 because those values are rounded up and so are inaccurate, so I'm not sure if we'd get the marks for it

otoolej2

Seannyyboy wrote: »

Because if you use the values of the masses relative to the electron, you get 1.022 instead of 0.78 because those values are rounded up and so are inaccurate, so I'm not sure if we'd get the marks for it

ouch, that would hurt. I'm think we will still get the marks doe. It would be a bit unfair otherwise.

2345

how did you guys answer the nuclear equation in Q10 one with the beta decay

smartz

Can somebody point out what is wrong with this answer for the beta decay:

Mass Defect:
(1.675x10^-27) - (1.673x10^-27) - (9.109x10^-31)
= 1.0891x10^-30
E=mc^2
E=(1.0891x10^-30)(2.998x10^8)^2
E=9.788835X10^-14 J
E = 611038.3993 eV
E= 0.611 MeV

Seannyyboy

smartz wrote: »

Can somebody point out what is wrong with this answer for the beta decay:

Mass Defect:
(1.675x10^-27) - (1.673x10^-27) - (9.109x10^-31)
= 1.0891x10^-30
E=mc^2
E=(1.0891x10^-30)(2.998x10^8)^2
E=9.788835X10^-14 J
E = 611038.3993 eV
E= 0.611 MeV

You're rounding up too much I think, try again with un-rounded values from the tables and you'll get 0.78

smartz

Seannyyboy wrote: »

You're rounding up too much I think, try again with un-rounded values from the tables and you'll get 0.78

ahh, thanks I did it with the unrounded values and got 0.78 MeV. Didn't think rounding would've made that much of a difference. Hope I don't lose too many marks.

Hon the Dubs

smartz wrote: »

ahh, thanks I did it with the unrounded values and got 0.78 MeV. Didn't think rounding would've made that much of a difference. Hope I don't lose too many marks.

Wait so are people thinking 0.78 MeV is right? I got that but thought it was a bit peculiar but I was nearly sure I was doing it right!
Would make my day if it is right
Also what did people say for the fundamental particle that experiences strong nuclear force?

smartz

Hon the Dubs wrote: »

Wait so are people thinking 0.78 MeV is right? I got that but thought it was a bit peculiar but I was nearly sure I was doing it right!
Would make my day if it is right
Also what did people say for the fundamental particle that experiences strong nuclear force?

I said quark, because I wasn't sure if protons counted as 'fundamental' particles since they are made up of other particles.