What do the signs in the 1st Law of Thermodynamics mean?

mkbh_10
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From the 1st law of thermodynamics we have

dU = ∂Q+∂W

but we also know

dU = Tds - pdv ,

i am confused about the + & - sign ?

Is it because volume & pressure are inversely dependent on each other
 
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Thread 'Off resonance driving of a MW/RF cavity'

Hello! Let's say I have a cavity resonant at 10 GHz with a Q factor of 1000. Given the Lorentzian shape of the cavity, I can also drive the cavity at, say 100 MHz. Of course the response will be very very weak, but non-zero given that the Loretzian shape never really reaches zero. I am trying to understand how are the magnetic and electric field distributions of the field at 100 MHz relative to the ones at 10 GHz? In particular, if inside the cavity I have some structure, such as 2 plates...
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