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

3 years ago
#1221
What would we write for compare and contrast radioactive decay to capacitor discharge
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3 years ago
#1222
(Original post by jcwh97)
To go from s^-1 to kms^-1 Mpc^-1 =

Take your value and multiply by 1000 and divide by 3.2x10^16 x 10^6

The answer in s^-1 will be roughly 2.0x10^-18 and in kms^-1 Mpc^-1 it will be about 65 - 70
Wouldn't you divide by 1000 and multiply by 3.1x10^22? The way you've put is from kms^-1Mpc^-1 to s^-1
0
3 years ago
#1223
(Original post by jcwh97)
To go from s^-1 to kms^-1 Mpc^-1 =

Take your value and multiply by 1000 and divide by 3.2x10^16 x 10^6

The answer in s^-1 will be roughly 2.0x10^-18 and in kms^-1 Mpc^-1 it will be about 65 - 70
Could you go through based on H0=2.31x10^-18 s-1 using your exact method above?
3 years ago
#1224
(Original post by leroythelost)
Hey how would guys say x-rays are produced?

How would it be different in a hospital machine because I have looked at two questions saying describe how x-rays are made and says in a hospital x-ray machine and the other one says an x-ray tube but the answers are different.
I would say: electrons are accelerated through a high p.d. at a metal target/plate. The kinetic energy of the electrons is converted into x-ray photons when the electrons hit the metal target or produced by a large deceleration of the electrons.
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3 years ago
#1225

wow.

Anyway 65*10^3 / 3.1*10^22.

H0 order of magnitude 10^-18
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3 years ago
#1226

Could you go through based on H0=2.31x10^-18 s-1 using your exact method above?
2.31x10^-18 x 3.1x10^16 x 10^6 / 10^3 = 71.6 kms^-1 Mpc^-1
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3 years ago
#1227
(Original post by jcwh97)
2.31x10^-18 x 3.1x10^16 x 10^6 / 10^3 = 71.6 kms^-1 Mpc^-1
That isnt the method you gave...
3 years ago
#1228
(Original post by fnatic NateDestiel)
wow.

Anyway 65*10^3 / 3.1*10^22.

H0 order of magnitude 10^-18
Would you exaplin where you got those number from thanks?
3 years ago
#1229

That isnt the method you gave...
Sorry i thought you wanted to convert the other way

Take your value and multiply by 3.16x10^16 x 10^6
And divide through by a 1000

Its the reverse
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3 years ago
#1230
(Original post by jcwh97)
Sorry i thought you wanted to convert the other way

Take your value and multiply by 3.16x10^16 x 10^6
And divide through by a 1000

Its the reverse
But you even said the correct conversion at the top of your description?!
3 years ago
#1231

Would you exaplin where you got those number from thanks?
65 given value.

*10^3 (km)

1pc = 3.1*10^16m

Mpc = 3.1*10^22

tbf mess around on your calculator and it yields the correct answer, I would recommend learning order of mangitudes i.e . critical density approx equal *10^-27 etc.
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3 years ago
#1232
(Original post by nothepreacher)
Awww take a rest! I still need to do a lot though And I am screwed as I don't remember much of AS stuff
I don't remember a single thing from AS. I hope they don't ask any definitions or circuit stuff from AS.
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3 years ago
#1233
(Original post by jcwh97)
LOL you are confusing me.

To convert s^-1 to kms^-1 Mpc^-1 you:

Multiply by a 1000 and divide through by 3.1x10^16 x 10^6

To convert kms^-1 Mpc^-1 to s^-1 you:

Multiply by 3.1x10^16 x 10^6 and divide through by a 1000
Okay just on your origianl post you stated s-1 to kms mpc-1 was the other way round haha it is okay about the mistake thanks anyway
3 years ago
#1234
(Original post by fnatic NateDestiel)
65 given value.

*10^3 (km)

1pc = 3.1*10^16m

Mpc = 3.1*10^22

tbf mess around on your calculator and it yields the correct answer, I would recommend learning order of mangitudes i.e . critical density approx equal *10^-27 etc.
Okay thanks do you have a list of magnitudes it is handy to know?
3 years ago
#1235

Okay thanks do you have a list of magnitudes it is handy to know?
H0 = 10^-18

Critical density = *10^-27
Age of universe = 1.5*10^10

Just off the top of my head, go through the past papers it will help you out!
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3 years ago
#1236

Okay just on your origianl post you stated s-1 to kms mpc-1 was the other way round haha it is okay about the mistake thanks anyway
Wait I think i said the wrong thing again LOL

This to confirm:

kms^-1 Mpc^-1 to s^-1

multiply by a 1000 and divide through by 3.16x10^16 x 10^6

s^-1 to kms^-1Mpc^-1

Multiply by 3.1x10^16 x 10^6 and divide through by a 1000

Thats definitely right
1
3 years ago
#1237
(Original post by jcwh97)
Wait I think i said the wrong thing again LOL

This to confirm:

kms^-1 Mpc^-1 to s^-1

multiply by a 1000 and divide through by 3.16x10^16 x 10^6

s^-1 to kms^-1Mpc^-1

Multiply by 3.1x10^16 x 10^6 and divide through by a 1000

Thats definitely right
Thank you, we got there in the end!!!!
3 years ago
#1238
Is this good for smoke alarms:

Americium-241 source emits alpha-particles into an ionisation chamber.
The ionisation chamber is an air-filled space between two electrodes.
The alpha particles ionise the air molecules, inducing a current which is detected by a current detector.
When smoke enters the ionisation chamber it absorbs the alpha particles which decreases the amount of ionisation and decreases the current.
The current detector will detect or recognise this decrease in current and set off the alarm.
0
3 years ago
#1239
(Original post by jcwh97)
Is this good for smoke alarms:

Americium-241 source emits alpha-particles into an ionisation chamber.
The ionisation chamber is an air-filled space between two electrodes.
The alpha particles ionise the air molecules, inducing a current which is detected by a current detector.
When smoke enters the ionisation chamber it absorbs the alpha particles which decreases the amount of ionisation and decreases the current.
The current detector will detect or recognise this decrease in current and set off the alarm.
Yes that is okay
3 years ago
#1240
(Original post by ETRC)
I don't remember a single thing from AS. I hope they don't ask any definitions or circuit stuff from AS.
I don't remember wave diffraction and all that. Or circuits! Just a bit of mechanics, even that I have lost touch with. I just hope they don't decide to be too synoptic.
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