Which of the following has/have zero average value in a plane electromagnetic wave?

Options

A. Both magnetic and electric fields
B. Electric field only
C. Magnetic field only
D. None of these

Explanation

To solve the question of which quantities have zero average value in a plane electromagnetic wave, we can follow these steps:

### Step 1: Understand the Nature of Electromagnetic Waves
Electromagnetic waves consist of oscillating electric and magnetic fields that propagate through space. These fields are sinusoidal in nature.

**Hint:** Recall that electromagnetic waves consist of oscillating electric and magnetic fields.

### Step 2: Analyze the Sinusoidal Nature
Both the electric field (E) and the magnetic field (B) in a plane electromagnetic wave can be represented mathematically as sinusoidal functions. For example, the electric field can be expressed as:
\[ E(t) = E_0 \sin(\omega t + \phi) \]
where \( E_0 \) is the amplitude, \( \omega \) is the angular frequency, and \( \phi \) is the phase.

**Hint:** Remember that sinusoidal functions oscillate between positive and negative values.

### Step 3: Determine the Average Value of a Sinusoidal Function
The average value of a sinusoidal function over one complete cycle is zero. This is because the positive and negative areas under the curve cancel each other out.

**Hint:** Consider how the area under the curve of a sine wave behaves over one complete cycle.

### Step 4: Apply This to Electric and Magnetic Fields
Since both the electric field and the magnetic field in a plane electromagnetic wave are sinusoidal, their average values over time will also be zero.

**Hint:** Think about the properties of sine waves and how they apply to both electric and magnetic fields.

### Step 5: Conclude the Answer
Thus, both the electric field and the magnetic field have an average value of zero in a plane electromagnetic wave.

**Final Answer:** Both the electric field and the magnetic field have zero average value in a plane electromagnetic wave.