The strength of magnetic field inside a long current-carrying straight solenoid is:

Options

A. more at the ends than at the centre
B. minimum in the middle
C. same at all points
D. found to increases from one end to the other

Explanation

To determine the strength of the magnetic field inside a long current-carrying straight solenoid, we can follow these steps:

### Step 1: Understand the formula for the magnetic field inside a solenoid
The magnetic field \( B \) inside a long solenoid can be expressed using the formula:
\[ B = \mu_0 n I \]
where:
- \( B \) is the magnetic field strength,
- \( \mu_0 \) is the permeability of free space (a constant),
- \( n \) is the number of turns per unit length of the solenoid,
- \( I \) is the current flowing through the solenoid.

### Step 2: Analyze the parameters in the formula
From the formula, we can see that:
- \( \mu_0 \) is a constant and does not change.
- \( n \) (the number of turns per unit length) is also constant for a given solenoid.
- \( I \) (the current) is constant throughout the solenoid.

### Step 3: Determine the uniformity of the magnetic field
Since \( B \) depends only on the constants \( \mu_0 \), \( n \), and the current \( I \), it indicates that the magnetic field strength \( B \) is uniform throughout the length of the solenoid. This means that the magnetic field strength does not vary from one point to another inside the solenoid.

### Step 4: Evaluate the options given in the question
Now, let’s evaluate the options provided:
- **A**: More at the ends than at the center - This is incorrect as the magnetic field is uniform.
- **B**: Minimum in the middle - This is also incorrect as the magnetic field is not minimum at any point.
- **C**: Same at all points - This is correct as we established that the magnetic field strength is uniform.
- **D**: Found to increase from one end to the other - This is incorrect as the magnetic field does not increase or decrease.

### Conclusion
The correct answer is **C**: The strength of the magnetic field inside a long current-carrying straight solenoid is the same at all points.

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