OCR Physics A G485 - Frontiers of Physics - 18th June 2015

Do we need to remember the Hubble constant? I can't find it in the formula booklet. Also can someone please explain how to convert it from its original form to SI units, I know it involves the conversion of parsecs but it;'d help thanks.

(edited 8 years ago)

Reply 1461

Tiwa

7

Original post by seizetoday

Cheers.

No problem! All the best for tomorrow.

Reply 1462

nothepreacher

18

Original post by Elcor

Don't worry about Helium because it's only one of quite a few marking points your allowed, and I don't understand it either.

Intensifier converts 1 X ray photon into many visible light photons (the X rays would otherwise mainly pass through the photographic film so this reduces the dose)
Or in a gamma camera, scintillator converts one gamma photon into many visible photons

Thank you! And good night all! Get some sleep. You are all smarty pants, and have worked hard, and you're going to be fine! :smile:

Reply 1463

Jim997

2

Original post by I Persia I

Do we need to remember the Hubble constant? I can't find it in the formula booklet. Also can someone please explain how to convert it from its original form to SI units, I know it involves the conversion of parsecs but it;'d help thanks.

No we don't. It's around 65 kms-1mpc-1 ...

So do 65 times ten to the 3/ 3.1 times ten to the 22

Reply 1464

Tiwa

7

Original post by I Persia I

Do we need to remember the Hubble constant? I can't find it in the formula booklet.

Nope. Either they'll give it to you or you'll have to work it out as there is no definite value of of the Hubble constant. It's believed to be between 50kms^-^1Mpc^-^1 and 100kms^-^1Mpc^-^1 .

Reply 1465

seizetoday

12

Original post by I Persia I

Do we need to remember the Hubble constant? I can't find it in the formula booklet. Also can someone please explain how to convert it from its original form to SI units, I know it involves the conversion of parsecs but it;'d help thanks.

Impossible to get an accurate Hubble constant. You usually work it out or get it given to you. To convert it into SI units is self explanatory

Reply 1466

seizetoday

12

Original post by Tiwa

No problem! All the best for tomorrow.

Yes! Thank you, you aswell

Reply 1467

I Persia I

16

Original post by Jim997

No we don't. It's around 65 kms-1mpc-1 ...

So do 65 times ten to the 3/ 3.1 times ten to the 22

Original post by Tiwa

Nope. Either they'll give it to you or you'll have to work it out as there is no definite value of of the Hubble constant. It's believed to be between 50kms^-^1Mpc^-^1

and 100kms^-^1Mpc^-^1 .

Original post by seizetoday

Impossible to get an accurate Hubble constant. You usually work it out or get it given to you. To convert it into SI units is self explanatory

Rep for y'all for being so smart and also being awake to help me :biggrin:

.

Reply 1468

Tiwa

7

Original post by I Persia I

Rep for y'all for being so smart and also being awake to help me :biggrin:

.

All the best for tomorrow!

Reply 1469

sarcastic-sal

2

Original post by Jmw123

In these formulas with the activity ones as well, when can and should I ignore the first bit e.g. I=I0 and just work out e to the power of the two things in this case ux, its in a lot of topics and I don't understand how you can do this.

Sometimes you will be given the fraction or percentage of the initial activity or initial no of nuclei or initial intensity etc. If for example the question was 'at a depth of 2cm, the intensity of ultrasound is 11% of the initial intensity, calculate the attenuation coefficient' they have given you I/Io in disguise - as here, I/Io = 11/100. You can then just manipulate the expression using logs to find mu.

(edited 8 years ago)

Reply 1470

I Persia I

16

Original post by Tiwa

All the best for tomorrow!

Cheers buddy you too!

Reply 1471

leroythelost

10

How do you define plasma?

Reply 1472

Tiwa

7

I ought to sleep now. All the best everyone.

Reply 1473

Raizel

3

Original post by sagar448

Guys why is the universe not infinite why was olber wrong? PLEASE HELP!

Olber's paradox is that, if the universe was infinite and static, then every line of sight would end on a star meaning that if you looked at the night sky it would just be bright because everywhere you look you will end up looking at a star, but look out side bro that's not the case, which means that the universe is not infinite and not static/homogeneous

Reply 1474

I Persia I

16

Original post by Raizel

Olber's paradox is that, if the universe was infinite and static, then every line of sight would end on a star meaning that if you looked at the night sky it would just be bright because everywhere you look you will end up looking at a star, but look out side bro that's not the case, which means that the universe is not infinite and not static/homogeneous