Question

When work done by a system was 20J. The increase in the internal energy of the system was 60J. The heat 'q' supplied to the system was:
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Answer 1

Given :-

☄ work done, w = -20J

☄ Internal energy = 60J

To find :-

The heat supplied to the system

Solution :-

using 1st law of Thermodynamics .i.e.,

❝ The net energy change in a closed system is equal to heat absorbed plus the work done by the system ❞

• ∆U = q + w

where,

∆U denotes change in Internal energy

q denotes heat gained or lost by the system

w denotes work done by the system

According to Question,

➠ ∆U = q + w

➠ 60 = q + (-20)

➠ q = 60 + 20

➠ q = 80J

thus, The heat supplied to the system is 80J.

|| Note :- For absorption of heat 'q' is +ve and for release 'q' is -ve ||

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Answer 2

Given:

The work done by a system was 20J. The increase in the internal energy of the system was 60J.

To find:

Heat supplied to system ?

Calculation:

• In these types of questions, it is best to apply 1ST LAW OF THERMODYNAMICS.

• Let heat change be ∆q, internal energy change be ∆U and work done be W.

$\Delta q =\Delta U + W$

• Since work was done by system, sign of W will be + , and since internal energy increased , ∆U will also have a + sign.

$\implies \Delta q =( + 60) + ( + 20)$

$\implies \Delta q =80 \: joule$

So, 80 Joule of energy was supplied into the system.