JEE Main · 2019 · 09 Jan 2019 · Shift 1 · Heat & Thermodynamics

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A gas can be taken from A to B via two different processes ACB and ADB. When path ACB is used 60 J of heat flows into the system and 30 J of work is done by the system. If path ADB is used work done by the system is 10 J. The heat flow into the system in path ADB is

(A)40 J✓ Correct
(B)80 J
(C)100 J
(D)20 J

Answer: (A)

Solution

Internal energy is a state function, so the change from

A

B

is the same along either path. Along

A C B

Δ U = Q - W = 60 - 30 = 30

J. Along

A D B

the same

Δ U = 30

J must hold, and with

W = 10

J the first law gives

Q = Δ U + W = 30 + 10 = 40

JEE Main · 2019 · 09 Jan 2019 · Shift 1 · Single correct option

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