In electromagnetic waves there is zero average value for

Options

A. electric field intensity
B. magnetic field intensity
C. electric field energy
D. magnetic field energy

Explanation

To solve the question, "In electromagnetic waves, there is zero average value for?", we need to analyze the average values of the electric field (E) and magnetic field (B) in electromagnetic waves.

### Step-by-Step Solution:

1. **Understanding Electromagnetic Waves**:
- Electromagnetic waves consist of oscillating electric (E) and magnetic (B) fields that are perpendicular to each other and to the direction of wave propagation.

2. **Average Value of Electric Field (E)**:
- The electric field can be represented as \( E(t) = E_0 \sin(kx - \omega t) \).
- To find the average value of E over one complete cycle, we calculate:
\[ \text{Average value of } E = \frac{1}{T} \int_0^T E(t) dt \]
where \( T \) is the period of the wave.
- The average of \( \sin(kx - \omega t) \) over one complete cycle is 0 because the positive and negative halves cancel each other out.

3. **Average Value of Magnetic Field (B)**:
- Similarly, the magnetic field can be represented as \( B(t) = B_0 \sin(kx - \omega t) \).
- The average value of B over one complete cycle is calculated in the same way:
\[ \text{Average value of } B = \frac{1}{T} \int_0^T B(t) dt \]
- The average of \( \sin(kx - \omega t) \) is also 0 for the same reason as above.

4. **Average Value of Electric Field Energy**:
- The energy density of the electric field is given by:
\[ U_E = \frac{1}{2} \epsilon_0 E^2 \]
- The average value of \( U_E \) can be calculated as:
\[ \text{Average } U_E = \frac{1}{2} \epsilon_0 E_0^2 \cdot \text{Average of } \sin^2(kx - \omega t) \]
- The average of \( \sin^2(kx - \omega t) \) over one complete cycle is \( \frac{1}{2} \), hence:
\[ \text{Average } U_E = \frac{1}{2} \epsilon_0 E_0^2 \cdot \frac{1}{2} = \frac{1}{4} \epsilon_0 E_0^2 \neq 0 \]

5. **Average Value of Magnetic Field Energy**:
- The energy density of the magnetic field is given by:
\[ U_B = \frac{1}{2} \frac{B^2}{\mu_0} \]
- The average value of \( U_B \) is calculated similarly:
\[ \text{Average } U_B = \frac{1}{2} \frac{B_0^2}{\mu_0} \cdot \text{Average of } \sin^2(kx - \omega t) \]
- Again, the average of \( \sin^2(kx - \omega t) \) is \( \frac{1}{2} \), leading to:
\[ \text{Average } U_B = \frac{1}{2} \frac{B_0^2}{\mu_0} \cdot \frac{1}{2} = \frac{1}{4} \frac{B_0^2}{\mu_0} \neq 0 \]

### Conclusion:
The average values of both the electric field (E) and the magnetic field (B) in electromagnetic waves are zero. However, the average values of the electric and magnetic field energies are not zero.

### Final Answer:
In electromagnetic waves, there is zero average value for the electric field (E) and the magnetic field (B).