Choose the correct expression of Intensity of em wave?

Options

A. Energy/ Area `xx` time
B. Energy/Area
C. Energy/ Area + time
D. None of the above

Explanation

To solve the question regarding the correct expression for the intensity of an electromagnetic wave, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Definition of Intensity**:
Intensity (I) of an electromagnetic wave is defined as the power (P) per unit area (A) over which the power is distributed. Mathematically, this is expressed as:
\[ I = \frac{P}{A} \]

2. **Relate Power to Energy**:
Power is defined as the rate at which energy is transferred or converted. Therefore, power can also be expressed as energy (E) per unit time (t):
\[ P = \frac{E}{t} \]

3. **Substitute Power in the Intensity Formula**:
We can substitute the expression for power into the intensity formula:
\[ I = \frac{P}{A} = \frac{E/t}{A} = \frac{E}{A \cdot t} \]

4. **Final Expression for Intensity**:
From the above derivation, we can conclude that the intensity of an electromagnetic wave can be expressed as:
\[ I = \frac{E}{A \cdot t} \]
This matches with the first option given in the question which states "energy divided by area into time".

5. **Evaluate the Options**:
- Option 1: \( \frac{E}{A \cdot t} \) (Correct)
- Option 2: \( \frac{E}{A} \) (Incorrect)
- Option 3: \( \frac{E}{A + t} \) (Incorrect)
- Option 4: None of the above (Incorrect)

### Conclusion:
The correct expression for the intensity of an electromagnetic wave is given by the first option: **energy divided by area into time**.

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