To make the field radial in a moving coil galvanometer

Options

A. The number of turns in the coil is increased
B. Magnet is taken in the form of horse-shoe
C. Poles are cylindrically cut
D. Coil is wound on aluminium frame

Answer

To make the magnetic field radial in a moving coil galvanometer, we need to ensure that the magnetic field lines are directed radially outward from the center of the coil. Here’s a step-by-step solution to achieve this:

### Step 1: Understand the Concept of Torque in a Galvanometer
The torque (\( \tau \)) experienced by the coil in a galvanometer is given by the equation:
\[ \tau = N \cdot I \cdot A \cdot B \cdot \sin(\theta) \]
where:
- \( N \) = number of turns in the coil
- \( I \) = current flowing through the coil
- \( A \) = area of the coil
- \( B \) = magnetic field strength
- \( \theta \) = angle between the magnetic field and the normal to the coil

### Step 2: Identify the Requirement for Radial Magnetic Field
For the magnetic field to be radial, it must originate from the north pole and terminate at the south pole in a manner that the field lines are directed outward from the center of the coil. This can be achieved by shaping the magnet appropriately.

### Step 3: Use a Cylindrical Magnet
To create a radial magnetic field, the magnet should be cut in a cylindrical manner. This means that the magnet should be shaped such that its poles are at the ends of a cylinder, allowing the magnetic field lines to radiate outward from the center of the coil.

### Step 4: Increase the Number of Turns in the Coil
Increasing the number of turns in the coil will enhance the torque experienced by the coil for a given current. This is beneficial because it allows for a more sensitive galvanometer, which can detect smaller currents.

### Step 5: Conclusion
Thus, to make the magnetic field radial in a moving coil galvanometer, the magnet should be cut in a cylindrical manner. This ensures that the magnetic field lines are directed radially outward, allowing for accurate measurements of current.

### Final Answer
The correct option to make the field radial in a moving coil galvanometer is to cut the magnet in a cylindrical manner.

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