By using felmings thumb rule we can state that when magnetic field is represented by curl fingers the thumb represents the direction of current thus they form 90 degree angle to each other so they are perpendicular to each other

The relation between the direction of current and the direction of magnetic field is perpendicular.

Explanation:

- Ampere's Right Hand Rule:
According to Ampere's Right Hand Rule, if you hold your right hand in such a way that your thumb points in the direction of the current, then the direction in which your fingers curl will give you the direction of the magnetic field.

- Magnetic Field Around a Straight Conductor:
Consider a straight conductor carrying current. The magnetic field produced around this conductor forms concentric circles. The direction of the magnetic field at any point can be determined using the right-hand rule. If you grip the conductor with your right hand, such that your thumb points in the direction of the current, the direction in which your fingers wrap around the conductor will indicate the direction of the magnetic field.

- Magnetic Field Inside a Solenoid:
A solenoid is a tightly wound coil of wire. When an electric current passes through a solenoid, a magnetic field is created inside the solenoid. The magnetic field lines run parallel to the axis of the solenoid. If you hold the solenoid in your right hand, with your fingers wrapped around the solenoid in the direction of the current, your thumb will point in the direction of the magnetic field inside the solenoid.

- Magnetic Field Around a Loop of Wire:
When a current flows through a loop of wire, a magnetic field is produced around the loop. The direction of the magnetic field can be determined using the right-hand rule. If you curl your right hand around the loop of wire in the direction of the current, your thumb will point in the direction of the magnetic field inside the loop.

From the above explanations, it is clear that the direction of the magnetic field is perpendicular to the direction of the current. This holds true for both straight conductors, solenoids, and loops of wire. Therefore, the correct answer is option 'C' - Perpendicular.