If work done by the system is 300 joule when 100 cal. Heat is supplied to it. The change in internal energy during the process is :-

Options

A. `-200` Joul
B. 400 Joul
C. 720 Joul
D. 120 Joul

Explanation

To find the change in internal energy during the process, we can use the first law of thermodynamics, which is given by the equation:

\[ \Delta U = Q + W \]

where:
- \(\Delta U\) is the change in internal energy,
- \(Q\) is the heat supplied to the system,
- \(W\) is the work done by the system.

### Step-by-Step Solution:

1. **Identify the heat supplied (Q)**:
The heat supplied to the system is given as 100 calories.

2. **Convert calories to joules**:
Since we need to work in joules, we convert calories to joules using the conversion factor \(1 \text{ cal} = 4.2 \text{ J}\).
\[ Q = 100 \text{ cal} \times 4.2 \text{ J/cal} = 420 \text{ J} \]

3. **Identify the work done (W)**:
The work done by the system is given as 300 joules. Since the work is done by the system, it is considered negative in the first law of thermodynamics.
\[ W = -300 \text{ J} \]

4. **Apply the first law of thermodynamics**:
Substitute the values of \(Q\) and \(W\) into the first law equation:
\[ \Delta U = Q + W \]
\[ \Delta U = 420 \text{ J} + (-300 \text{ J}) = 420 \text{ J} - 300 \text{ J} \]

5. **Calculate the change in internal energy**:
\[ \Delta U = 120 \text{ J} \]

Thus, the change in internal energy during the process is **120 joules**.