When a graph between two physical quantities is straight line, the two quantities are

Options

A. constant
B. independent of each other
C. directly proportional to each other.
D. inversely proportional to each other.

Answer

To determine the relationship between two physical quantities when their graph is a straight line, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Graph**: A straight line graph indicates a linear relationship between the two quantities plotted on the axes.

2. **Identify the Types of Relationships**: There are three main types of relationships that can exist between two quantities:
- Constant: One quantity does not change regardless of the other.
- Directly Proportional: As one quantity increases, the other quantity also increases at a constant rate.
- Inversely Proportional: As one quantity increases, the other quantity decreases.

3. **Analyze the Straight Line**:
- If the graph is a straight line that passes through the origin (0,0), it indicates that the two quantities are directly proportional. This means that if one quantity doubles, the other also doubles.
- If the line is straight but does not pass through the origin, it indicates a constant relationship, but this is not the case we are considering here.

4. **Conclusion**: Since the question specifies a straight line graph, we conclude that the two quantities are directly proportional to each other.

5. **Final Answer**: Therefore, the answer is that when a graph between two physical quantities is a straight line, the two quantities are directly proportional to each other.