Question

Work done by a system is taken to be

a) positive

b) negative

c) zero

d) varies according to situation

Answer #1

If you use the notation of 1st law as follows:

Q - W = dE

then,

if system is expanded ( i.e. system DOES work on the surroundings) then, W must be positive

b)

If we use the notation

Q + W = dE

then,

the System is losing energy, due to the expansion, so we must account this as NEGATIVE.

Therefore, vaeries according the situation

Typically, modern thermodynamics courses use the first notation

Q - W = dE

then, the Work done must be accounted possitive

choose A

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