Physics Question Help

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?

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

7. B
10. A
14. D

OHhhh, now I get it!

Sarcasm, right?

Maaaaaaybe.

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

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

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

No way is that wrong!

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

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?

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?

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

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

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