Which of the following is proportional to energy density in magnetic field B:

Options

A. `1/B`
B. `1/(B^(2))`
C. B
D. `B^(2)`

Explanation

To solve the question regarding which of the following is proportional to energy density in a magnetic field B, we can follow these steps:

### Step 1: Understand the concept of energy density in a magnetic field
The energy density (u) in a magnetic field is defined as the amount of energy stored per unit volume in the magnetic field.

### Step 2: Use the formula for magnetic energy density
The formula for energy density in a magnetic field is given by:
\[ u = \frac{B^2}{2\mu_0} \]
where:
- \( u \) is the energy density,
- \( B \) is the magnetic field strength,
- \( \mu_0 \) is the permeability of free space (a constant).

### Step 3: Analyze the formula
From the formula \( u = \frac{B^2}{2\mu_0} \), we can see that the energy density \( u \) is directly proportional to the square of the magnetic field strength \( B^2 \).

### Step 4: Identify the correct option
Since the energy density is proportional to \( B^2 \), we conclude that the correct option is the one that states energy density is proportional to \( B^2 \).

### Final Answer
Thus, the correct answer is option D, which states that energy density in the magnetic field B is proportional to \( B^2 \).

---