Solar cnstant is __________ cal `cm^(2)`/mm.

Options

A. 2
B. 4
C. 6
D. 8

Answer

To solve the question "Solar constant is __________ cal `cm^(2)`/mm," we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Concept of Solar Constant**:
- The solar constant refers to the amount of solar electromagnetic radiation per unit area. It is a measure of the solar energy received at the top of the Earth's atmosphere.

2. **Identify the Measurement Units**:
- The units mentioned in the question are calories per square centimeter per millimeter (cal `cm^(2)`/mm).

3. **Recall the Value of Solar Constant**:
- The solar constant is approximately 1.94 calories per square centimeter per millimeter.

4. **Round the Value**:
- For practical purposes, this value is often rounded to 2 calories per square centimeter per millimeter.

5. **Fill in the Blank**:
- Therefore, we can conclude that the solar constant is approximately 2 cal `cm^(2)`/mm.

### Final Answer:
Solar constant is **2 cal `cm^(2)`/mm**.

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