A magnetic needle is kept in a non uniform magnetic field . It experiences

Options

A. a force and torque
B. a force but not a torque
C. a torque but not a force
D. Neither a tarque nor a froce

Explanation

To solve the question about the behavior of a magnetic needle in a non-uniform magnetic field, we can follow these steps:

### Step 1: Understand the Concept of a Magnetic Needle
A magnetic needle, such as a compass needle, is a small magnet that aligns itself with the magnetic field. It has a north and south pole, and it experiences forces and torques when placed in a magnetic field.

**Hint:** Remember that a magnetic needle behaves like a tiny bar magnet.

### Step 2: Define Non-Uniform Magnetic Field
A non-uniform magnetic field is one where the magnetic field strength varies from one point to another. This means that the magnetic field at one location (B1) can be different from the magnetic field at another location (B2).

**Hint:** Think about how the strength and direction of the magnetic field can change in different locations.

### Step 3: Analyze Forces Acting on the Magnetic Needle
In a non-uniform magnetic field, the magnetic forces acting on the two poles of the needle (north and south) will be different due to the variation in the magnetic field strength. This creates a net force on the needle.

**Hint:** Consider how the unequal forces on the two poles of the needle lead to a resultant force.

### Step 4: Analyze Torque Acting on the Magnetic Needle
The torque (τ) experienced by the magnetic needle is given by the formula τ = m × B, where m is the magnetic moment and B is the magnetic field. In a non-uniform magnetic field, since the forces on the two poles are unequal, the torque will also be present.

**Hint:** Remember that torque is related to the force and the distance from the pivot point (the center of the needle).

### Step 5: Conclusion
Since the magnetic needle experiences both a net force due to the difference in magnetic field strength at its poles and a torque due to the non-uniformity of the field, we conclude that the correct answer is:

**Answer:** The magnetic needle experiences both a force and a torque.

### Final Answer
The correct option is A: a force and a torque.

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