A student fixes a sheet of white paper on a drawing board. He places a bar magnet in the centre of it. He sprinkles some iron filings uniformly around the bar magnet. Then he taps the board gently and observes that the iron filings arrange themselves in particular pattern.
The closer field lines indicate:

Options

A. Magnetic field in that region is weak
B. Magnetic field in that region is strong.
C. Magnetic field in that region is zero.
D. North and South poles are closer.

Explanation

To solve the question regarding the arrangement of iron filings around a bar magnet and the significance of the closer field lines, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Setup**:
- A bar magnet has two poles: the North (N) pole and the South (S) pole. When placed on a sheet of paper and surrounded by iron filings, the filings will respond to the magnetic field created by the magnet.

**Hint**: Remember that magnets have two distinct poles that create a magnetic field around them.

2. **Observation of Iron Filings**:
- When the board is tapped, the iron filings align themselves along the magnetic field lines. This pattern visually represents the magnetic field around the bar magnet.

**Hint**: Think about how magnetic fields can be visualized through the behavior of magnetic materials like iron filings.

3. **Identifying Magnetic Field Lines**:
- The pattern formed by the iron filings indicates the direction and strength of the magnetic field. The lines emerge from the North pole and curve around to the South pole.

**Hint**: Recall that magnetic field lines show the direction of the magnetic force and are denser where the field is stronger.

4. **Analyzing the Density of Field Lines**:
- The closer the field lines are to each other, the stronger the magnetic field in that area. Conversely, where the lines are spaced further apart, the magnetic field is weaker.

**Hint**: Consider how the spacing of lines can indicate the intensity of the magnetic field.

5. **Conclusion**:
- Therefore, the closer field lines indicate a stronger magnetic field. This means that the regions where the field lines are densely packed correspond to areas of higher magnetic strength.

**Hint**: Summarize that the density of field lines directly relates to the strength of the magnetic field.

### Final Answer:
The closer field lines indicate that the strength of the magnetic field is strong in that region.