Nice video, it helped me a lot! But, I think you made a mistake with the 1st law of thermodynamics equation. It is supposed to be Q = U - W , according to CIE A level Physics Syllabus (2025-2027).
Then CIE are wrong for writing it this way. This version implies that W is the work done on the gas, when that value should just be negative in this case.
If you are studying chemistry then you would write the first law as U=Q+W. In physics we write it as Q=U+W. This is due to different sign conventions adopted in the two subjects.
So for the thermal physics 3.6.2 on the AQA spec, it’s not required to talk about the first law of thermodynamics, only if doing the optional engineering on paper 3?
Isnt work done by the gas negative I’m so confused cause in my textbook it says it’s negative and then save my exams says it’s negative at one point then positive at another section
I don't know where you're from, but my exam board allows us to use both U = Q + W and U = Q - W depending on whether we take work as negative or positive. Essentially, when the gas is compressed, work is done ON it, so its internal energy is increased. When the gas expands, it must do work to push itself outwards, so it loses internal energy. The easiest thing to do imo is to reason out whether the gas is gaining or losing energy, then see whether the formula contains a + W or - W. Substitute W with a positive or negative value to make things work properly. Work out practice questions and you should get used to when W is positive and negative. Good luck, and if there's something I didn't explain clearly let me know
lord have mercy
Lads I’m finished
Amazing Video Man !! you made everything so simple now i can revise anytime with your videos
Nice video, it helped me a lot! But, I think you made a mistake with the 1st law of thermodynamics equation. It is supposed to be Q = U - W , according to CIE A level Physics Syllabus (2025-2027).
Then CIE are wrong for writing it this way. This version implies that W is the work done on the gas, when that value should just be negative in this case.
Thank you!
@@ScienceShortsyeah in my text book they have given the equation as U= Q + W where Q is thermal energy supplied and W is work done on the gas
If you are studying chemistry then you would write the first law as U=Q+W. In physics we write it as Q=U+W. This is due to different sign conventions adopted in the two subjects.
Perfect summary thanks for the video
0:52 uhhhh i dont?
So for the thermal physics 3.6.2 on the AQA spec, it’s not required to talk about the first law of thermodynamics, only if doing the optional engineering on paper 3?
Correct (and in other boards)
Isnt work done by the gas negative I’m so confused cause in my textbook it says it’s negative and then save my exams says it’s negative at one point then positive at another section
I don't know where you're from, but my exam board allows us to use both U = Q + W and U = Q - W depending on whether we take work as negative or positive.
Essentially, when the gas is compressed, work is done ON it, so its internal energy is increased. When the gas expands, it must do work to push itself outwards, so it loses internal energy. The easiest thing to do imo is to reason out whether the gas is gaining or losing energy, then see whether the formula contains a + W or - W. Substitute W with a positive or negative value to make things work properly.
Work out practice questions and you should get used to when W is positive and negative. Good luck, and if there's something I didn't explain clearly let me know