The magnitude of magnetic flux is expressed as ?

Options

A. `phi = BA xx cos theta `
B. `phi = B + A cos theta `
C. `phi = BA sin theta `
D. `phi = BA // cos theta`

Explanation

To find the magnitude of magnetic flux, we can follow these steps:

### Step 1: Understand the Definition of Magnetic Flux
Magnetic flux (Φ) is defined as the product of the magnetic field (B) and the area (A) through which the field lines pass. It is also influenced by the angle (θ) between the magnetic field lines and the normal (perpendicular) to the surface area.

### Step 2: Use the Formula for Magnetic Flux
The formula for magnetic flux is given by:
\[ \Phi = B \cdot A \cdot \cos(\theta) \]
Where:
- \( \Phi \) is the magnetic flux,
- \( B \) is the magnetic field strength,
- \( A \) is the area through which the magnetic field lines pass,
- \( \theta \) is the angle between the magnetic field lines and the normal to the surface.

### Step 3: Identify the Correct Expression
From the options provided:
1. \( \Phi = B A \cos(\theta) \)
2. \( \Phi = B + A \cos(\theta) \)
3. \( \Phi = B A \sin(\theta) \)
4. \( \Phi = \frac{B A}{\cos(\theta)} \)

The first option \( \Phi = B A \cos(\theta) \) matches the formula we derived for magnetic flux.

### Conclusion
Thus, the correct expression for the magnitude of magnetic flux is:
\[ \Phi = B A \cos(\theta) \]