# Physics Question Help

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For Q7:

I used Wiens Displacement

so

Wavelength x Temp = const

Wavelength1 x 750 = wavelength2 X 960

so

Wavelength2 = 750W1 / 960 = 0.78W1 = Option A but apparently answer is Option B?

I used Wiens Displacement

so

Wavelength x Temp = const

Wavelength1 x 750 = wavelength2 X 960

so

Wavelength2 = 750W1 / 960 = 0.78W1 = Option A but apparently answer is Option B?

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For Q10:

Option A looks exactly like the Suns spectrum but has been slightly red-shifted but the answer is Option B?

Option A looks exactly like the Suns spectrum but has been slightly red-shifted but the answer is Option B?

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For Q14:

I used the equation:

PV = 1/3Nmc^2

We're told PV is constant after a 1/3 of the gas is removed. so I thought

1/3 * 1/3 Nmc^2 = 1/3 Nm 3x10^5

Cancelling down this gives me the answer

C^2 = 9x10^5 which is Option D but the answer is Option C?

I used the equation:

PV = 1/3Nmc^2

We're told PV is constant after a 1/3 of the gas is removed. so I thought

1/3 * 1/3 Nmc^2 = 1/3 Nm 3x10^5

Cancelling down this gives me the answer

C^2 = 9x10^5 which is Option D but the answer is Option C?

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#6

(Original post by

For Q7:

I used Wiens Displacement

so

Wavelength x Temp = const

Wavelength1 x 750 = wavelength2 X 960

so

Wavelength2 = 750W1 / 960 = 0.78W1 = Option A but apparently answer is Option B?

**Afrrcyn**)For Q7:

I used Wiens Displacement

so

Wavelength x Temp = const

Wavelength1 x 750 = wavelength2 X 960

so

Wavelength2 = 750W1 / 960 = 0.78W1 = Option A but apparently answer is Option B?

Last edited by golgiapparatus31; 1 month ago

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(Original post by

For Wien's displacement law, the absolute temperature is used, so you need to convert to kelvin

Note that pV is constant, but not T. so use pV = nRT to work out the new temperature, then use pV = 1/3 Nmc^2

**golgiapparatus31**)For Wien's displacement law, the absolute temperature is used, so you need to convert to kelvin

Note that pV is constant, but not T. so use pV = nRT to work out the new temperature, then use pV = 1/3 Nmc^2

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#12

(Original post by

Maaaaaaybe.

**Afrrcyn**)Maaaaaaybe.

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(Original post by

Well, I think 10 is A. Could be wrong, but I'm pretty sure

**ItsStarLordMan**)Well, I think 10 is A. Could be wrong, but I'm pretty sure

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#14

(Original post by

I mean that's what I put but apparently it's not! Hoping someone can explain it to me before Monday

**Afrrcyn**)I mean that's what I put but apparently it's not! Hoping someone can explain it to me before Monday

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**golgiapparatus31**)

For Wien's displacement law, the absolute temperature is used, so you need to convert to kelvin

Note that pV is constant, but not T. so use pV = nRT to work out the new temperature, then use pV = 1/3 Nmc^2

(Original post by

No way is that wrong!

**ItsStarLordMan**)No way is that wrong!

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#16

**Afrrcyn**)

I mean that's what I put but apparently it's not! Hoping someone can explain it to me before Monday

(Original post by

Why would I use pV = 1/3 Nmc^2, if T isn't even in that equation, would I not use 1/2mc^2 = 3/2 kT?

**Afrrcyn**)Why would I use pV = 1/3 Nmc^2, if T isn't even in that equation, would I not use 1/2mc^2 = 3/2 kT?

[Alternative method below]

Last edited by golgiapparatus31; 1 month ago

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#17

(Original post by

For Q14:

I used the equation:

PV = 1/3Nmc^2

We're told PV is constant after a 1/3 of the gas is removed. so I thought

1/3 * 1/3 Nmc^2 = 1/3 Nm 3x10^5

Cancelling down this gives me the answer

C^2 = 9x10^5 which is Option D but the answer is Option C?

**Afrrcyn**)For Q14:

I used the equation:

PV = 1/3Nmc^2

We're told PV is constant after a 1/3 of the gas is removed. so I thought

1/3 * 1/3 Nmc^2 = 1/3 Nm 3x10^5

Cancelling down this gives me the answer

C^2 = 9x10^5 which is Option D but the answer is Option C?

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(Original post by

1/3 of the gas is removed, so 2/3 N molecules are left. Using this, we get the answer

**golgiapparatus31**)1/3 of the gas is removed, so 2/3 N molecules are left. Using this, we get the answer

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#19

(Original post by

Ohhh, yes, yes. I was using 1/3 and not 2/3! Any idea for Q10? Thanks for the help!

**Afrrcyn**)Ohhh, yes, yes. I was using 1/3 and not 2/3! Any idea for Q10? Thanks for the help!

But the change for each one is not the same, so the first 2 lines cannot remain the same distance apart, so it can't be A. We find that it is B, because it can't be C or D

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(Original post by

As you say, there is a red-shift of the wavelengths.

But the change for each one is not the same, so the first 2 lines cannot remain the same distance apart, so it can't be A. We find that it is B, because it can't be C or D

**golgiapparatus31**)As you say, there is a red-shift of the wavelengths.

But the change for each one is not the same, so the first 2 lines cannot remain the same distance apart, so it can't be A. We find that it is B, because it can't be C or D

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